Plato's Theaetetus dramatizes a search for a definition of knowledge, testing perception, true opinion, and accounts without reaching a settled answer. This deck covers the dialogue's uncertain dating, its frame scene, the three definitions, the Protagorean argument, and the interpretive difficulties the introduction raises.
1 / 197
Chapter 1 · Question
What two features make the Theaetetus's date uncertain, per the introduction?
WakeCards · wakecards.com · Big ideas. Quick review.
Chapter 1 · Answer
The introduction says the dialogue mixes traits of Plato's early and late writings: its style, humour, and Socratic profession of ignorance resemble early works, while its subject matter links it to the later Sophist. The author argues no definite date is indicated, estimating it could not have been written earlier than 390 BCE, when Plato was about thirty-nine.
WakeCards · wakecards.com · Big ideas. Quick review.
Arrow keys move between cards. Space or Enter flips.
All questions and answers
Every card in the deck, in reading order. Click a chapter to expand. The reviewer above uses the same content.
Section 13 cards
What two features make the Theaetetus's date uncertain, per the introduction?
The introduction says the dialogue mixes traits of Plato's early and late writings: its style, humour, and Socratic profession of ignorance resemble early works, while its subject matter links it to the later Sophist. The author argues no definite date is indicated, estimating it could not have been written earlier than 390 BCE, when Plato was about thirty-nine.
Chapter 1
What is the purpose of the dialogue's introductory scene with Euclides and Terpsion?
The introduction says the preface's real intention is to create interest in Theaetetus, who has just been carried up from the army at Corinth in a dying state. The expectation of his death recalls the promise of his youth and the famous conversation with Socrates shortly before Socrates' trial and death. The author notes the narrative device is then dropped and never used again.
Chapter 1
How does the introduction describe Theaetetus's intellectual progress in the dialogue?
Theaetetus is a disciple of Theodorus the geometer, and the author says he is a youthful Socrates, matching a fair soul with an ungainly face. At first too modest to speak, he grows enthusiastic, shows talent for drawing distinctions, and foresees consequences of his answers. Though long feeling the 'pang of philosophy,' he cannot yet move from mathematics to metaphysics, until Socrates helps conduct him from a theory of sense to a theory of ideas.
Chapter 1
Section 24 cards
According to the chapter, why is Theodorus reluctant to defend Protagoras?
Theodorus is too old to learn Socrates' game of question and answer and prefers digressions to the main argument because they are easier to follow. He had early 'run away' from philosophy and was absorbed in mathematics. The chapter notes the mathematician is not capable of giving a reason like the dialectician, so Theodorus could not be the chief respondent, though he may be appealed to when his master's honor is at stake.
Chapter 2
What functions does the chapter say God assigns to Socrates in the Theaetetus?
The chapter says Socrates is assigned by God the functions of a man-midwife, who delivers men of their thoughts, and he is present under this character throughout the dialogue. He is also described as a true prophet with insight into men's natures who can divine their future, and who knows that sympathy is the secret power that unlocks their thoughts.
Chapter 2
What three stages does the chapter say the dialogue examines in defining knowledge?
The chapter says the dialogue proceeds from lower to higher through three stages, in which perception, opinion, and reasoning are successively examined. First, the confusion between knowledge and specific kinds of knowledge is cleared up. Then Socrates analyzes Theaetetus' first definition, 'Knowledge is sensible perception,' identifying it with Protagoras' 'Man is the measure' and grounding it in Heraclitean flux.
Chapter 2
Why does the chapter say the Protagorean thesis is ultimately shown to be unsustainable?
The chapter says the Protagorean thesis is pronounced suicidal because Protagoras' adversaries are as good a measure as he is and deny his doctrine. His reply that perception may be true at any given instant is shown inconsistent with the Heraclitean foundation: if flux extends to every change in every instant, no thought or word can be detained even for an instant, so sensible perception tumbles to pieces.
Chapter 2
Section 34 cards
What are the three successive definitions of knowledge Theaetetus offers?
Theaetetus first proposes that knowledge is sensible perception. After that is set aside, he proposes that knowledge is true opinion, but the possibility of false opinion is raised and no answer is given. Finally he proposes true opinion with definition or explanation, whose various interpretations are all set aside, so the dialogue ends inconclusively.
Chapter 3
Why does the chapter say knowledge is not the same as true opinion?
The chapter argues that knowledge is not true opinion, citing the Athenian dicasts (jurors) as an example. They have true opinion but not knowledge. This objection shows that true opinion alone is insufficient to count as knowledge, which is why the discussion moves on to consider true opinion combined with definition or explanation.
Chapter 3
What two difficulties does the chapter identify for students of the Theaetetus?
First, the student is uncertain how far Plato's account of Protagoras's theory can be trusted. Second, the student is uncertain how far, and in which parts of the dialogue, Plato is expressing his own opinion. The chapter attributes both difficulties to the dramatic character of the work.
Chapter 3
What does the chapter say about Socrates and Plato's own views in the dialogues?
The chapter argues that readers should not assume Socrates always speaks for Plato. It notes that the Sophists are sometimes right and Socrates wrong, that few modern readers fail to side with Protagoras in the dialogue named after him, and that arguments are often put into Socrates' mouth that must have seemed untenable to Plato too.
Chapter 3
Section 44 cards
How does the chapter describe the intellectual climate of Plato's age?
The author argues it was an age when analysis had outrun knowledge, and dialectic was being used spuriously. The great speculative philosophies were degenerating into Eristic; the Megarians were making knowledge impossible, the Cynics stripped virtue of what made it desirable, and godless materialists who would not believe what they could not hold in their hands could not be argued with because they could not argue.
Chapter 4
What difficulties does the chapter say the Greek mind faced in Plato's era?
The author argues that limits between imagination and abstraction, and between the old and new worlds, were not yet fixed. The Greeks had no words for 'subject' and 'object' and no distinct conception of them, though they hovered about the question. Analysis of sense and of thought were equally difficult, and they were confused by trying to solve these through general theories rather than facts.
Chapter 4
What does the chapter say Plato does in the Theaetetus, and what does he not do?
The author argues Plato gathers up and compares the sceptical tendencies of his age but does not seek to reconstruct a theory of knowledge from them, since the time for such a theory had not arrived. Plato offers many contributions, following philosophy into mythology and showing extreme abstractions are self-destructive, but he rejects explanations of knowledge with germs of truth, such as resolving the compound into the simple.
Chapter 4
How does the frame narrative bring Theaetetus and the dialogue to the reader?
Terpsion comes to Megara seeking Euclides, who met Theaetetus being carried to Athens, badly wounded at Corinth and suffering camp dysentery. Euclides recalls Socrates prophesying the youth would be great if he lived. Euclides took notes of the conversation, filled them out at leisure, and had Socrates correct them. He omits the interlocutory words, and a servant reads the roll aloud.
Chapter 4
Section 54 cards
What two kinds of number does Theaetetus say he has distinguished?
Theaetetus describes square numbers such as 4, 9, and 16, composed of equal factors and representing figures with equal sides, and oblong numbers such as 3, 5, 6, and 7, composed of unequal factors and representing figures with unequal sides. He notes he has never reached a similar general conception of knowledge, though he has often tried.
Chapter 5
Why does Socrates call his answer about kinds of knowledge too much and too little?
Socrates says Theaetetus enumerated several kinds of knowledge but failed to explain their common nature. He compares it to answering "What is clay?" with a list of image-makers', potters', and oven-makers' clays instead of saying clay is moistened earth. The answer gives examples rather than the general definition sought.
Chapter 5
What does Socrates mean by calling himself a midwife?
Socrates says men as well as women have labour pains, and he inherited the midwife's art from his mother. He cannot bring forth thoughts of his own, since the god will not allow it, but he helps others deliver their ideas. He warns that some patients produce abortions or lose their offspring through bad upbringing, and some return to him later.
Chapter 5
How does Socrates connect knowledge as perception with Protagoras?
When Theaetetus says knowledge is perception, Socrates identifies this with Protagoras's claim that man is the measure of all things. Using the example of one wind felt hot by one person and cold by another, he explains that "is" means "appears" and "appears to him" means "he feels," so feeling, appearance, and perception coincide with being.
Chapter 5
Section 64 cards
According to the Heraclitean doctrine in this section, what produces whiteness and the sensation of whiteness?
The eye and the appropriate object come together and give birth to whiteness and the sensation of whiteness. The eye becomes a seeing eye, not sight, and the object becomes white, not whiteness. No other combination would produce the same effect. All sensation is resolved into a similar combination of agent and patient, neither of which can be conceived separately.
Chapter 6
What is Socrates' objection about dreams and madness to the doctrine that knowledge is perception?
Socrates notes that in madness and dreaming perception is false, and half our life is spent dreaming, so no one can say whether at this instant we are dreaming. Even madmen's fancies are real to them at the time. If knowledge is perception, how can true and false be distinguished in such cases? He then states Protagoras' answer: what is different is entirely different, and each combination yields a different perception.
Chapter 6
How does Protagoras answer the objection that the same wine tastes pleasant when well and unpleasant when ill?
Protagoras denies the continuity of phenomena: what is different is entirely different, and each agent and patient has a different power. Socrates well and Socrates ill are different; the wine is pleasant to the well Socrates and unpleasant to the ill one. Nothing else can give the same impression, and the combination is absolute at each moment. My sensation alone is true, and true to me only.
Chapter 6
What does Socrates find absurd about Protagoras' 'man is the measure' doctrine?
Socrates says he likes the doctrine that what appears is, but wonders why Protagoras did not declare that a pig, a dog-faced baboon, or any monster with sensation is a measure of all things. If all sensations are true and every man is his own judge, then Protagoras need not be a paid instructor, and Socrates' art of midwifery and all dialectic would be folly.
Chapter 6
Section 71 cards
How does Socrates refute the claim that knowledge is sensible perception?
Socrates argues that if seeing is knowing, a man who closes his eyes and remembers what he saw may remember and not see, and therefore remember and not know. Since he can remember without seeing, and seeing is knowing, he may remember and not know—a reductio ad absurdum of the hypothesis that knowledge is sensible perception.
Chapter 7
Section 83 cards
How does Socrates turn Protagoras's 'man is the measure' against itself?
Socrates argues that all mankind judges some people wise and others foolish, so most people deny Protagoras's thesis. If truth depends on majority opinion, Protagoras's own truth is false for most. And if those who deny he speaks truly speak truly, then he does not speak truly, so his truth is true to nobody, including himself.
Chapter 8
What distinction does Socrates draw between sensations and judgments?
Socrates is willing to grant Protagoras that immediate sensations like hot and cold are to each person as they appear. But he insists this cannot be extended to judgments or opinions, since there are great differences in men's understandings. Even those who extend the relativity to right and wrong will not say everyone is equally a measure of expediency.
Chapter 8
What does the Thales maid-servant story illustrate about philosophers?
Socrates cites the witty maid-servant who saw Thales fall into a well and said he was so eager to know heavenly things that he could not see what was before his feet. The author applies this to all philosophers: they are unacquainted with the world and hardly know whether their neighbor is a man or an animal, always searching into the essence of man.
Chapter 8
Section 93 cards
How does Socrates refute Protagoras's claim that man is the measure?
Socrates argues the expedient concerns the future, about which people err. He asks whether an untrained man is as likely as a physician to know when he will get a fever, or a vine-grower a better judge of an ungarnered vintage. Protagoras would never have amassed a fortune if every man could judge the future for himself, so he is compelled to admit he is a measure.
Chapter 9
Why does Socrates substitute 'through' for 'with' when discussing perception?
Theaetetus says he perceives sights with the eye and sounds with the ear. Socrates replies that nice distinctions of words are sometimes pedantic but sometimes necessary, and proposes 'through' instead. The senses are not like Trojan warriors hidden in the horse; they have a common centre of perception where all meet, a principle able to compare them and therefore distinct from them.
Chapter 9
Why is knowledge not perception, according to the argument about abstractions?
Socrates distinguishes facts of sense perceived through bodily organs from abstractions like sameness, difference, likeness, unlikeness, and being, which the soul perceives by herself. The essence of hardness, or that hardness is and is the opposite of softness, is slowly learned by reflection and experience. Mere perception does not reach being, therefore fails of truth, and has no share in knowledge.
Chapter 9
Section 104 cards
In the wax block analogy, what causes false opinion?
The wax block is the gift of Memory in the soul, receiving seals of sensations one wishes to remember. False opinion arises when perception and knowledge fail to correspond: seeing two people imperfectly at a distance and putting the seal on the wrong object, or seeing only one while knowing both. Error is thus a confusion of thought and sense.
Chapter 10
What objection about numbers undermines the wax block theory?
Socrates raises it himself: errors occur where there is no confusion of mind and sense, as in arithmetic. No one confuses the man in his thoughts with the horse in his thoughts, but he may err in adding five and seven. Since these are purely mental conceptions, the dilemma returns: either false opinion does not exist, or a man knows what he does not know.
Chapter 10
What distinction does the aviary analogy introduce about knowledge?
The aviary images the mind as initially empty, later stocked with birds representing forms of knowledge, some in groups and some single. Socrates distinguishes 'possessing' knowledge from 'having' it, as a man may possess a garment he does not wear or birds caged but not in hand. The original hunt differs from taking a caged bird in hand.
Chapter 10
What is thinking, according to the chapter's account of false opinion?
Thinking is the mind conversing with herself, carried on in question and answer until she no longer doubts but determines and forms an opinion. False opinion would consist in saying to yourself that one thing is another. But Socrates presses that no one in his senses ever fancies an ox is a horse or that two are one, so transplacement seems inconceivable.
Chapter 10
Section 114 cards
Why does Socrates reject the claim that true opinion is knowledge, using orators and judges?
Socrates argues that an orator cannot convey true knowledge of crimes to judges who were not present; he can only persuade them. The judge may form a true opinion and judge truly, yet without having witnessed the events. If true opinion were knowledge, the judges could not have judged without knowledge, so true opinion must differ from knowledge.
Chapter 11
What three meanings of 'explanation' does Socrates examine in the definition of knowledge?
Socrates considers explanation as (1) the reflection or expression of one's thoughts, which anyone not deaf and dumb can do; (2) the enumeration of elements, such as the hundred planks of Hesiod's waggon; and (3) perception of difference, as when one recognizes a particular snub-nosedness as Theaetetus. Each meaning is tested and found to leave knowledge still undefined.
Chapter 11
How does the alphabet example (the syllable SO) undermine the theory that knowledge is true opinion with definition?
The syllable SO consists of two letters, a sibilant and a vowel, of which no further explanation can be given. One cannot be ignorant of either letter yet know both of them. If syllables have no parts, they are original elements without explanation; but a syllable cannot be known if its letter remains unknown. Socrates notes children learn letters before syllables, and in music notes are clearer than combinations.
Chapter 11
What is Socrates' final verdict on Theaetetus' proposed definitions of knowledge?
Socrates concludes that knowledge is neither perception, nor true opinion, nor definition accompanying true opinion. He tells Theaetetus his intellectual offspring are not worth rearing, and asks whether he is still in labour or has brought all he has to say to birth. Socrates describes his art as midwifery, like his mother's, and denies comparing himself with the wise.
Chapter 11
Section 124 cards
How does the chapter distinguish modern 'experience' from Theaetetus's 'all knowledge is sensation'?
The chapter says modern 'experience' implies a starting point in sense and a return to sense, but also includes all intervening processes of reasoning and imagination. The necessary connection between sense and reasoning does not measure their relative importance: the inductive portion of a science may be small, as in mathematics or ethics, compared with what the mind attains by reasoning on very few facts.
Chapter 12
What ambiguity in Protagoras's 'Man is the measure' does the chapter say must be cleared up?
The chapter identifies two questions often confused: whether Protagoras merely asserted the relativity of knowledge to the human mind, or whether he denied an objective standard of truth. It notes relativity has sometimes been confounded with uncertainty, and argues that because knowledge is subjective or relative, we are not therefore deprived of tests or criteria of truth.
Chapter 12
According to the chapter, what did Protagoras probably intend with his thesis, and what did he fail to analyze?
The chapter argues Protagoras probably intended neither to deny nor affirm an objective standard of truth. Absorbed with the absoluteness of perception, he did not consider whether 'man' meant man in the higher or lower sense. He did not analyze whether 'man' meant concrete or abstract man, any man or some men, universal consent or individual private judgment; such distinctions lay beyond his age.
Chapter 12
How does the chapter characterize Plato's treatment of Protagoras?
The chapter says Plato treats Protagoras much as Aristotle later treats Plato: he does not attempt to understand him from his own point of view, but entangles him in a more advanced logic. Protagoras is supposed to reply with Megarian quibbles. The chapter finds palpable unfairness in the arguments about sight and memory, and says Theodorus justly charges Socrates with going beyond the truth.
Chapter 12
Section 134 cards
How does Plato's account of Heracleitus differ from Heracleitus's actual fragments?
The author argues there is nothing in Heracleitus's fragments justifying Plato's account. Heracleitus's philosophy had two elements: change, and law or measure pervading change. He had no analysis of sensible perception such as Plato attributes to him, never said change means every sort of change, and expressly distinguished general from particular understanding. Plato really targets the degenerate Heracliteans of his own age, not the master.
Chapter 13
Why does the Heraclitean flux doctrine threaten Protagorean sensationalism?
If all things change at every moment in all sorts of ways, nothing is fixed or defined, so there is no sensible perception and no true word by which anything can be described. The author notes Protagoras would not have accepted this argument, since Socrates first conflates him with Heracleitus and the Ephesian successors, then disproves both knowledge and sensation.
Chapter 13
What distinction about the senses does the author call a great advance in psychology?
Recognizing the senses as organs of a presiding nature, so we see or feel through them rather than by them, a verbal distinction Socrates says is not pedantic. A further step is acknowledging that abstract notions such as Being, sameness, and unity are creations of the mind working on sense impressions. The author connects this to Plato's claim that knowledge lies in reasoning about feelings, not in the feelings themselves.
Chapter 13
Why is false opinion a difficulty, and how does Plato first explain it?
We must either know or not know what is presented, so error seems impossible; the author notes later answers about degrees of knowledge belong to a later stage of discussion. Plato first explains false opinion as a confusion of mind and sense when a mental impression does not match a sense impression. He then discards this because it cannot cover errors in arithmetic, where no thought-sense combination occurs.
Chapter 13
Section 144 cards
Why does Plato reject the mind-as-enclosure and mind-as-wax figures?
The author argues Plato discards both figures because they do not really solve the question of how we make mistakes. Error is essentially negative, a not-knowing; if we knew an error we would no longer be in error. Figures of speech may persuade the multitude but can never be the real foundation of a psychology.
Chapter 14
How does Plato argue for true opinion distinct from knowledge, and why is it criticized?
Plato uses law-court rhetoric: a rhetorician cannot give the jury all the facts but may truly persuade them of an act. The author argues this makes true opinion a right conclusion from imperfect knowledge, purely accidental, really one man persuading another who lacks the means to know. The author says Plato would have done better to call true opinion a contradiction in terms.
Chapter 14
What three explanations of logos does the chapter consider, and their flaws?
First, logos as the reflection of thought in speech: anyone not dumb can say what they think, so mere speech is not knowledge. Second, enumeration of elementary parts: only definition with right opinion, and enumeration of particulars is endless. Third, possession of a characteristic mark, like definition by genus and difference: but this is equally necessary for right opinion.
Chapter 14
What flaw does Plato find in defining knowledge as a compound of known elements?
Plato asks how we can know a compound whose simple elements are unknown: can two unknowns make a known, or a whole differ from its parts? The author notes experience answers yes, since we may know a compound we cannot analyze, and parts united may exceed the parts separated, as with number four or a chemical compound.
Chapter 14
Section 154 cards
According to the chapter, why is dividing the mind into separate faculties misleading?
The chapter argues the division of mind into faculties, powers, or virtues is too deeply rooted in language to eliminate but gives a false impression. On reflection, all our faculties easily pass into one another and are bound together in a single mind or consciousness. This mental unity is apt to be concealed from us by the distinctions of language, and any separation of things we cannot see or exactly define, though perhaps necessary, is a fertile source of error.
Chapter 15
What does the chapter call 'the fallacy of the looking-glass'?
It is the illusion of looking into our own minds as if thoughts or feelings were written down in a book. The chapter argues we cannot look at the mind unless we have the eye that sees; we can only look out of the mind at thoughts, words, and actions of ourselves and others. What we dimly recognize within is not experience but the suggestion of an experience, gathered from observing the world.
Chapter 15
How does the chapter evaluate the three laws of thought?
The chapter argues the first law (All A = A) is an identical proposition, a mere word or symbol claiming to be a proposition. The other two (Nothing can be A and not A; Everything is either A or not A) are untrue because they exclude degrees and the mixed modes and double aspects under which truth is often presented. To say man is man is unmeaning; to say he is free or necessary and cannot be both is only half true.
Chapter 15
What did Protagoras claim, and how does the chapter characterize it?
Protagoras said 'Man is the measure of all things' and 'All knowledge is perception.' The chapter calls this not an error but a step in the right direction: it was the subjective counterpart to the objective doctrine 'All is flux.' Later thinkers came to see knowledge was neither sense nor opinion, with or without explanation, nor expression of thought, nor enumeration of parts, nor addition of characteristic marks.
Chapter 15
Section 164 cards
According to the chapter, why has mankind repeatedly returned to a sensational philosophy?
The chapter says that amid the fleeting nature of sensible objects and the fluctuation of philosophical opinions, later thinkers sought fixed points in outward objects. Any knowledge beyond them implied logical processes of uncertain correctness, so the tired mind rested on perception of outward objects alone once the idols of philosophy and language were stripped off.
Chapter 16
How does the chapter distinguish sensation from the higher truths of philosophy and religion?
The chapter argues that higher truths, though derived from experience, are universal and unseen, belonging to all times, and are proved by their comprehensiveness and mutual consistency and by agreement with history and experience. Sensation, by contrast, is of the present only, isolated, and shifts in successive moments, following the eye or ear rather than reason.
Chapter 16
What role does the chapter assign to the mind in the simplest sensation?
The chapter states that the simplest sensation involves an unconscious or nascent operation of the mind. A mere sensation is a confused impression until number introduces order, and the conception of an external object or the power to discriminate numbers, forms, and colours comes from the mind, not the senses. Object, sense, and mind are inseparably bound together.
Chapter 16
How does the chapter describe space as prior to objects of sense?
The chapter calls space a third nature containing objects of sense, a negative idea that became positive, derived chiefly through sight and feeble in the blind. It seems continuous but divisible by lines or points, and mathematics develops its unchangeable properties. No limit can be set to it, nor can an indivisible portion be conceived, yet even the infinite and infinitesimal can be reasoned about.
Chapter 16
Section 174 cards
What does the chapter say about the question whether space exists in the mind or outside it?
The chapter argues the question has no meaning. Without space the mind cannot conceive the body, and therefore cannot conceive itself. It rejects the notion that space is merely a quality or condition of individual minds, calling this a confusion of the individual and the universal, and notes that if space is only mental, then the earth, the starry heaven, and ourselves are equally an illusion.
Chapter 17
How does the chapter explain the apparent necessity of our idea of space?
The chapter says this necessity differs only slightly from the necessity of other ideas like weight and motion. It may be explained by our having been taught it, with inherited truth never contradicted in experience and so confirmed by it. Much of what is called the a priori intuition of space is really the conception of geometrical figures whose properties mathematical analysis reveals, with certainty increased by consequences holding good.
Chapter 17
What does the chapter say about the history of the idea of space?
The chapter insists our idea of space, like other ideas, has a history. The Homeric poems contain no word for it; later Greek philosophy lacks the Kantian notion, having only definite 'place' or 'the infinite.' To Plato in the Timaeus it is known only as the 'nurse of generation.' The necessity of our idea of space has grown with the human mind and been made by ourselves.
Chapter 17
How does the chapter compare time with space?
Time is described as the form of the inward, as space is the form of the outward. We cannot think of successive sensations without time, just as we cannot think of outward objects without space. Time is the vacancy of thoughts, without limit, and like space it has been realized gradually, with no more notion of time than of space in the Homeric poems or Hesiodic cosmogony.
Chapter 17
Section 183 cards
What is the 'natural memory' and who has it?
The natural memory is allied to sense and depends on the intensity or largeness of a perception, or on a strong emotion connected with it. Children, barbarians, and animals appear to have it. It is necessarily limited in range, and the author says its limitation is its strength. Later life brings a second, educated memory of system and arrangement.
Chapter 18
How does language change the child's relation to words and images?
At first every word carries a colour of sense, an indistinct picture of the object. In later years the name holds only the universal or class word, and the more abstract the notion, the more vacant the image. The author argues all mental operations, including sense perception, become a synthesis of sensations, words, and conceptions.
Chapter 18
What mental inheritance do animals lack, according to the chapter?
Animals have memory in various degrees and elements of imagination, and share physical inheritance of form, scent, hearing, sight, and instincts. But they lack the mental inheritance of thoughts and ideas handed down by tradition, and they lack language, which the author calls the great educator of mankind. In humans, language grows simultaneously with the faculties.
Chapter 18
Section 194 cards
How does the chapter describe the relation between sense and reflection?
The chapter argues that no line can be drawn between the powers of sense and reflection; they pass imperceptibly into one another. Recollection is present in sight as sight is in recollection, and no sense impression fails to recall differences of form, number, and colour. The terms 'inward and outward,' 'mind and body' are best conceived as differences of degree passing into differences of kind.
Chapter 19
How does the chapter answer writers who call the inward sense a fading of the outward?
The author argues this leaves out half the phenomenon: the mind is not only withdrawn from the world of sense but introduced to a higher world of thought, where it is trained and educated. By use the inward thought becomes more defined, and reflection is not feebler than sense but of a higher and more comprehensive nature.
Chapter 19
How does the chapter describe the senses as instruments of the mind?
The senses are not merely 'holes set in a wooden horse' but instruments of the mind organically connected with it. There is no use of them without some use of words, latent logic, or previous experience. Sensation is complex and relative though apparently simple; the senses confirm and support one another, and many intuitions inseparable from sense result from complicated reasonings.
Chapter 19
How does the chapter explain our perception of distance and position?
The chapter says the experienced eye judges relations and distance though the retina receives only colour, including gradations of light and shade. From these delicate differences we chiefly derive ideas of distance and position, comparing near with distant objects. This is a language of 'large and small letters' learned all our life, aided by two eyes, nerve strain, and teaching from more experienced judgments.
Chapter 19
Section 204 cards
What does the chapter say happens to the youthful metaphysician who adopts idealism?
The author argues the young metaphysician is delighted by the discovery that mind is all, but soon finds all things remain as they were—laws of motion, properties of matter, qualities of substances. He only differs from others in the use of a word, and gains no more evidence of the supernatural than before, while he himself becomes unsettled.
Chapter 20
According to the chapter, what happens to uncertainty in sense appearances when science applies its tests?
The author argues that whatever uncertainty exists in the appearances of nature arises only from the imperfection or variation of human senses, or possibly from deficiency in certain branches of knowledge. When science is able to apply her tests, the uncertainty is at an end—so the appeal to the fallibility of sense is really an illusion.
Chapter 20
What does the chapter say about the mind in relation to facts and ideas?
The author argues we cannot get beyond facts, but neither can we draw a line separating facts from ideas. The mind is not something separate from them but included in them, and they in the mind, both having distinctness and individuality. Reducing mind to a succession of feelings is like viewing a wide prospect by inches through a microscope; mind ceases to exist when it loses continuity.
Chapter 20
What does the chapter say about the link between theories of knowledge and ethical philosophy?
The author argues that, on the whole, the higher standard of duty has gone hand in hand with the higher conception of knowledge. It is Protagoras who seeks to adapt himself to the opinions of the world, maintaining all knowledge is sensation; it is Plato who rises above them, basing the virtues on the idea of good. The author concedes Stoics were materialists and materialists have shown virtues.
Chapter 20
Section 214 cards
Why does the author say a sensational philosophy appeals to the man of the world?
The author argues a lower philosophy is easier to apprehend and a lower way of life easier to follow, so it draws support from general practice. It gives people back, in generalized form, the results of their own experience and their reflections upon life, requiring the least mental effort. Many who were metaphysicians in youth acquiesce in things as they appear with age.
Chapter 21
What three answers does the author give for why 'all knowledge is sensation' allies with a lower ethics?
The author lists three: first, because it is easier to understand and practise; second, because it is fatal to the pursuit of ideals, whether moral, political, or religious; third, because it deprives us of the means and instruments of higher thought, of any adequate conception of the mind, of knowledge, of conscience, and of moral obligation.
Chapter 21
Who does the author credit with nearly all the good done in the world, and how do they differ from Epicureans?
The author argues nearly all the good (and some evil) done in the world is the work of enthusiasts and idealists, apostles and martyrs — not the gentle Epicurean type. These leaders personified ideas, sometimes were their victims, always sought a truth or ideal they fell short of, and died disappointed of their hopes while lifting humanity out of the slough.
Chapter 21
What does the author say psychology lacks as a science, according to the appended essay?
The author argues psychology has gained bulk but not clearly true growth, and only claims the authority of a science while remaining an hypothesis or outline fillable many ways by individual fancy. Its basis — consciousness of ourselves and uncertain observation of others — is precarious; its relations to other sciences are undetermined; it is a hastily run-up building with weak foundations that never drew a line between facts and opinions.
Chapter 21
Section 224 cards
Why does the author deny popular Psychology the status of a science?
The author argues it cannot proceed by the Inductive Method like Physical Sciences, lacks the necessity of Mathematics, and does not argue from abstract notions like Metaphysic. Instead it is made up of scattered observations. Some of these observations are of great value and free from doubt, but when we try to combine them into a single system, the links are apt to be mere words.
Chapter 22
What certain facts does the author list as examples of psychological knowledge?
The author lists: the influence of mind over body and body over mind; the power of association, which recalls other persons and events not always but often; the effect of habit, strongest when least disturbed by reflection; the real but not unlimited freedom of the human will; consciousness, the reference of sensations and thoughts to ourselves; and the distinction of the 'I' and 'Not I.'
Chapter 22
Why can the mind not fully observe itself while thinking?
The author argues the mind, when thinking, cannot survey that part of itself used in thought. It can only be contemplated in the past, in the history of the individual or of the world, which is the scientific method of studying the mind. No microscope has ever seen into thought, and no reflection has supplied the missing link between mind and matter.
Chapter 22
What practical use does the author assign to the study of these psychological fragments?
The author argues these fragments can never become science in the ordinary sense but are a real part of knowledge and valuable in education. Self-examination can be pursued alone by attending to one's own mind, and much can be learned about one's own character and others' if one makes the mind 'sit down' and look at itself. The great, if not only, use is practical: to know human nature and our own nature as it truly is.
Chapter 22
Section 234 cards
According to the chapter, what are the six natural states or stages of the mind?
The chapter lists: (1) sensation, in which the mind is almost latent or quiescent; (2) feeling, or inner sense, when the mind is just awakening; (3) memory, described as decaying sense that can recollect the buried past; (4) thought, where images pass into abstract notions; (5) action, moving toward or away from some end; and (6) the composition or admixture of these in various degrees.
Chapter 23
How does the chapter say knowledge of the mind is chiefly obtained, rather than from individual self-observation?
The author argues that knowledge of the mind is not largely derived from an individual observing himself. Rather, it is the growing consciousness of the human race, embodied in language, acknowledged by experience, and corrected over time by literature and philosophy. A great part of it is found in early Greek thought, though in Plato's Theaetetus it has not yet become fixed.
Chapter 23
What do the 'eccentric thinkers' who rebelled against the Aristotelian point of view object to?
According to the chapter, these thinkers, found in medieval times and after the Reformation, held that there has been too much analysis and too little synthesis, too much division of the mind into parts and too little conception of it as a whole or in relation to God and the universe. They thought plurality and unity were not duly adjusted, tending to absorb personality into the universal or divine and deny the matter-mind distinction.
Chapter 23
Why does the chapter say common language's psychology is not an exact science, and how may truth still be approached?
The chapter states that common language represents the mind from different and even opposite points of view, which cannot all be equally true, and words do not always correspond to facts. Yet from diversity of statements and opinions a nearer approach to truth may be obtained than from any one alone. It also tends to correct itself, being gradually brought nearer to the common sense of mankind.
Chapter 23
Section 244 cards
According to the chapter, what is the firmer ground of Psychology?
The author argues that the firmer ground of Psychology is not the consciousness of inward feelings but the observation of external actions—actions not only of ourselves but of the innumerable persons we encounter in life. This is because the mind cannot survey its whole domain at once, any more than the eye can take in the whole body at a glance.
Chapter 24
Why does the chapter claim Psychology is an unverifiable hypothesis?
The author argues Psychology is not merely an hypothesis but one that, unlike hypotheses of Physics, can never be verified. It rests only on the general impressions of mankind, and there is little or no hope of adding in any considerable degree to our stock of mental facts.
Chapter 24
What error does the chapter attribute to language in studying mind?
The author argues we are apt to suppose that when two or more words describe faculties or processes of the mind, real differences correspond to them—but this is not the case. Nor can we determine how far such differences exist or by what degree or kind they are distinguished. Figures of speech similarly fill the vacancy of knowledge and conceal rather than reveal truth.
Chapter 24
How does the chapter describe the relation of heredity to nurture?
The author notes heredity was known to the ancients and exercises considerable influence on human character, yet we cannot calculate what proportion this birth-influence bears to nurture and education. We cannot pursue the mind into embryology, only trace its growth after birth; how much is due to soil versus latent seed is impossible to distinguish, so we must not exaggerate heredity's wonder.
Chapter 24
Section 253 cards
According to the chapter, why can Psychology never be a connected system?
The chapter argues Psychology is necessarily a fragment, not a connected system, because we cannot define or limit the mind—only describe it. We can collect information and enumerate its principal subjects, rehabilitating it as a collection of facts bearing on human life, part of the history of philosophy, and an aspect of Metaphysic. It is a fragment of a science that in all probability can never make great progress or attain much clearness or exactness.
Chapter 25
What does the chapter say about the claim that consciousness assures us of freedom?
The chapter calls 'consciousness' the most treacherous word in the study of the mind, used in many senses and rarely minutely analyzed. It says consciousness is a kind of attention we pay to ourselves, intermittent rather than continuous, and that its sphere has been exaggerated. It states that the claim consciousness assures us of freedom is an illusion: there may be real freedom without consciousness of it, and consciousness of freedom without the reality.
Chapter 25
How does the chapter describe the different mental processes and the faculties based on them?
The chapter lists processes such as 'I perceive,' 'I feel,' 'I think,' 'I want,' and 'I remember,' which are distinguished in thought but intermingle, and are all latent in any mental operation. It argues that the conception of different faculties or virtues is precarious, because each passes into the other and they are all one in the mind itself—ever-varying phases or aspects of the same mind or person.
Chapter 25
Section 264 cards
What does the chapter say about the laws of association?
The chapter calls the phrase "laws of association" confusing, since association is described as the most capricious and uncertain sort of phenomenon. It notes that seeing or hearing one of two things previously experienced together tends to suggest the other, and that like may recall like or its opposite. Yet it also stresses that the process is often intermittent, not continuous, and that the mind can think of things in isolation.
Chapter 26
According to the chapter, is the mind wholly dependent on association?
No. The chapter states that both science and poetry are made up of associations or recollections, but it insists the mind is not wholly dependent on them, having also the power of origination. New thoughts may arise spontaneously, by the action of the mind itself or by latent influence of the body, as when we wake or after violent exercise.
Chapter 26
What does the chapter say about the completeness of Psychology as a science?
The chapter admits there is no perfect or ideal Psychology: it is not a connected unity of knowledge like Chemistry, Physiology, or Mathematics. It rests on few facts, and beyond them we fall into conjectures and verbal discussions. The facts are disjointed, and their causes run up into other sciences that cannot be traced from one to the other.
Chapter 26
How does the chapter say Psychology should be studied?
The chapter argues Psychology should be natural, not technical, and intelligible to common understanding, since it deals with familiar common things. It should argue from ordinary rather than exceptional phenomena, distinguish higher and lower elements of human nature, assert the unity of the faculties, knowledge, God and law, and recognize the difference between will and affections and between reason and passions.
Chapter 26
Section 274 cards
How does Euclid explain the origin of his written record of Socrates' conversation?
Euclid says he took notes as soon as he got home and filled them up from memory at leisure. Whenever he went to Athens he asked Socrates about any point he had forgotten, and on returning made corrections, so he had nearly the whole conversation written down.
Chapter 27
What does Euclid say he omitted from the conversation, and why?
Euclid says he omitted the interlocutory words 'I said' and 'I remarked,' which Socrates used when speaking of himself, and also 'he agreed' or 'disagreed' in the answers. He left them out for convenience, lest the repetition of them should be troublesome.
Chapter 27
How does Theodorus describe Theaetetus's natural gifts and character?
Theodorus calls him unrivalled in quickness of apprehension, exceedingly gentle, and the most courageous of men. He says quick, retentive wits usually have quick tempers and are mad rather than courageous, while steadier sorts prove stupid at study; Theaetetus moves surely and smoothly in enquiry, flowing silently like a river of oil.
Chapter 27
What prophecy of Socrates about Theaetetus does Euclid say was fulfilled?
Euclid recalls that Socrates, shortly before his own death, conversed with Theaetetus as a youth, admired his genius, and said he would most certainly be a great man if he lived. Euclid notes this prediction, like all Socrates' predictions, was remarkably fulfilled.
Chapter 27
Section 284 cards
Why does Socrates say Theodorus's praise of Theaetetus should be attended to?
Socrates distinguishes praise of physical resemblance from praise of virtue or wisdom. He argues that if Theodorus praises the mental endowments of either of them, the one praised should naturally wish to be examined and should be willing to exhibit himself. Since Theodorus, who is not given to jesting, praised Theaetetus as he has praised no other, Socrates says now is the time to examine him.
Chapter 28
What does Socrates identify as the same as wisdom?
Socrates leads Theaetetus to agree that learning makes one wiser about what one learns, that the wise are wise by wisdom, and that men are wise in what they know. From this he concludes that wisdom and knowledge are the same. He then declares the real difficulty: defining what knowledge itself is.
Chapter 28
Why does Socrates reject Theaetetus's first answer listing the sciences and crafts?
Theaetetus answers that geometry and the other sciences he learns from Theodorus, plus cobbling and other crafts, are knowledge. Socrates objects that he gave many diverse things when asked for one simple thing. The question was not the subjects or number of arts, but the nature of knowledge in the abstract. Naming an art is not defining knowledge.
Chapter 28
What does Socrates's clay illustration show about defining knowledge?
Socrates imagines someone asked what clay is and answered with clay of potters, oven-makers, or brick-makers. He says this is ridiculous: the questioner still would not understand the nature of clay, and naming an art when asked what knowledge is amounts to replying 'a knowledge of this or that.' The simple answer would be that clay is moistened earth.
Chapter 28
Section 293 cards
How did Theaetetus and his companions classify numbers into two classes?
They divided all numbers into two classes: square or equilateral numbers, made up of equal factors multiplying into one another and compared to square figures; and oblong numbers, such as three and five, made up of unequal factors (greater times less or less times greater) and compared to oblong figures with unequal sides.
Chapter 29
What did Theaetetus's group call the roots of oblong numbers, and why?
The sides whose squares are equilateral plane numbers were called lengths or magnitudes; the lines that are roots of oblong numbers were called powers or roots. The name reflects that they are commensurable with the lengths not in linear measurement but in the value of the superficial content of their squares, with the same applying to solids.
Chapter 29
Why does Socrates compare himself to a midwife, and what does he say midwives cannot do?
Socrates says he practices midwifery of the mind, helping others bring forth thoughts. He notes that no woman still able to conceive attends others, only those past bearing, since Artemis honors those like herself and human nature cannot know an art without experience. Midwives also know who is pregnant and can arouse or soothe pangs.
Chapter 29
Section 304 cards
What does Socrates say his art of midwifery examines in young men?
Socrates says his midwifery attends men's souls rather than bodies, and its triumph is thoroughly examining whether the thought a young man's mind brings forth is a false idol or a noble and true birth. Like midwives he is barren: the god compels him to be a midwife but does not allow him to bring forth, so he claims no wisdom of his own.
Chapter 30
Why does Socrates claim those who leave him too soon end badly?
Socrates says many, in ignorance or self-conceit, despise him or fall under others' influence and leave too soon. They lose the children he had delivered through bad upbringing and stifle what remained through evil communications, preferring lies and shams to truth, until they see themselves as great fools. He cites Aristeides, son of Lysimachus, among them.
Chapter 30
What does Theaetetus first propose knowledge is?
After Socrates' exhortation, Theaetetus says he would be ashamed not to try his best. He reasons that he who knows perceives what he knows, and so, as far as he can see at present, knowledge is perception. Socrates calls this bravely said and proposes they examine together whether it is a true birth or a mere wind-egg.
Chapter 30
How does Socrates illustrate Protagoras' 'man is the measure' doctrine?
Socrates uses the same wind blowing: one person may be cold and another not, or one slightly and another very cold. Since 'appears to him' means 'he perceives,' the wind is cold to the cold person and not to the other, rather than cold absolutely. Socrates notes Protagoras stated this in a parable to the common herd but told 'his Truth' in secret to disciples.
Chapter 30
Section 314 cards
According to Socrates, what does Homer's 'golden chain' signify?
Socrates urges the golden chain in Homer as his strongest argument, interpreting it as the sun: so long as the sun and heavens move in their orbits, all things human and divine exist and are preserved; if their motions ceased, all things would be destroyed and turned upside down.
Chapter 31
How does Socrates define colour in relation to perception?
Applying the principle that nothing is self-existent, Socrates says white, black, and every other colour arises from the eye meeting the appropriate motion. Colour is neither the active nor the passive element but something passing between them, peculiar to each percipient; he doubts colours appear the same to a dog or another animal as to us.
Chapter 31
What three axioms does Socrates say conflict in the dice example?
Socrates lists: nothing can become greater or less in number or magnitude while remaining equal to itself; without addition or subtraction there is no increase or diminution, only equality; and what was not before cannot be afterwards without becoming. The six dice are more than four yet fewer than twelve, so these axioms fight one another.
Chapter 31
What does Socrates say about wonder and philosophy?
When Theaetetus says his head swims contemplating the contradictions, Socrates replies that Theodorus rightly saw his philosophical nature, since wonder is the feeling of a philosopher and philosophy begins in wonder. He cites the genealogist who said Iris, messenger of heaven, is the child of Thaumas (wonder).
Chapter 31
Section 324 cards
What does Socrates call the 'uninitiated' who deny invisible action or generation?
Socrates describes the uninitiated as people who believe in nothing but what they can grasp in their hands, refusing to allow that action, generation, or anything invisible has real existence. Theaetetus calls them hard and impenetrable mortals, and Socrates agrees, calling them outer barbarians, contrasting them with the more ingenious 'brethren' whose mysteries he is about to reveal.
Chapter 32
According to the 'brethren,' how are sense and object of sense generated?
The first principle is that all is motion, of two forms, active and passive, endless in number. From their union and friction arises an endless progeny with two forms, sense and the object of sense, born at the same moment. Each sense—hearing, seeing, smelling, heat, cold, pleasure, pain, desire, fear—has its kindred object, so each variety of colour corresponds to a variety of sight, and so on.
Chapter 32
How does Socrates illustrate the birth of whiteness and sight?
When the eye and the appropriate object meet, they give birth to whiteness and the connatural sensation, which neither could produce alone. Sight flows from the eye and whiteness from the object; the eye becomes not sight but a seeing eye, and the object becomes not whiteness but a white thing, whether wood or stone. Socrates says this holds for all sensible objects, which have no absolute existence but are generated by motion in intercourse.
Chapter 32
What objection about dreams and madness does Socrates raise against 'knowledge is perception'?
Socrates notes that dreams, diseases, madness, and illusions of hearing and sight seem to refute the esse-percipi theory, since in these states we have false perceptions. Far from saying everything that appears is, we should rather say nothing that appears is. Theaetetus agrees, unable to claim madmen or dreamers think truly when they imagine they are gods or flying. Socrates then asks how to determine whether we are now asleep or awake.
Chapter 32
Section 334 cards
How does Socrates use the dream/waking analogy against sense-perception?
Socrates notes that since life is divided between sleeping and waking, the soul affirms the truth of whatever thoughts are present in each state, and we are equally confident in both. Madness differs only in that its periods are not equal. He asks whether truth should be determined by duration of time, which Theaetetus calls ridiculous, and neither can determine by other means which opinion is true.
Chapter 33
What happens when the sick Socrates drinks the wine, on this account?
The combination of the wine and the sick Socrates produces a different result: bitterness in the tongue and the motion of bitterness in the wine, which becomes not bitterness but something bitter, while Socrates becomes not perception but percipient. Since agent and patient are both altered, the same object meeting a different subject produces a different result.
Chapter 33
What conclusion does Socrates draw about the relation between agent and patient?
Socrates concludes that agent and patient are or become in relation to one another, bound by a law to each other but not to any other existence nor each to himself. So anyone saying a thing is or becomes must say it is or becomes to, of, or in relation to something else, and must not say anything is or becomes absolutely.
Chapter 33
How does Socrates restate the identity of perception and knowledge at the end?
Socrates says the meaning turns out the same whether with Homer and Heracleitus one says all is motion and flux, with Protagoras that man is the measure of all things, or with Theaetetus that, given these premises, perception is knowledge. He calls this Theaetetus's newborn child and proposes testing whether it is worth rearing or a wind-egg.
Chapter 33
Section 344 cards
What does Socrates find absurd about Protagoras calling man the measure of all things?
Socrates argues that if truth is only sensation and each person is sole judge of his own perceptions, then Protagoras should have begun his book on Truth by declaring a pig or dog-faced baboon the measure of all things. Socrates asks why Protagoras should then be esteemed as a wise teacher and well paid, if everyone is equally the measure of their own wisdom.
Chapter 34
What does Socrates say about arguments from probability in matters of importance?
Socrates has Protagoras reply that his accusers bring in the gods and talk of man being degraded to the level of brutes, but offer no proof, only probability. He warns that admitting probability and figures of speech in such important matters is unacceptable, since a mathematician arguing from likelihoods in geometry would not be worth an ace.
Chapter 34
How does Theaetetus distinguish perceiving from knowing in the letters example?
Theaetetus says that when we see letters we do not understand, we see and know the figure and colour of the letters, and when we hear foreign speech we hear and know the elevation or depression of the sound. But we do not perceive or know what grammarians and interpreters teach about them. So perception of a thing differs from understanding its meaning.
Chapter 34
What difficulty does Socrates raise about memory and knowledge?
Socrates asks whether a man who has known something and preserves a memory of it can fail to know that which he remembers when he remembers it. Theaetetus calls the supposition monstrous. Socrates then links this to the definition that knowledge is perception, asking whether every man knows what he has seen, and whether memory is of things learned and perceived.
Chapter 34
Section 354 cards
How does Socrates refute the claim that knowledge is perception?
Socrates argues that if seeing is knowing, then a man who saw something and remembers it with his eyes closed both remembers (knows) it and does not see (does not know) it. Since knowing and not knowing the same thing is impossible, knowledge and perception must be distinguished. Theaetetus concedes the argument shows a manifest impossibility.
Chapter 35
What does Socrates mean by comparing himself to a cock that crows without winning?
Socrates says that he and Theaetetus, like disputers (Eristics), were satisfied with mere verbal consistency and pleased to gain an advantage in argument rather than seeking truth. He suspects they have unconsciously fallen into the error of that class of persons, and he calls this walking away and crowing without victory.
Chapter 35
What does Socrates say about defending Protagoras's position?
Socrates notes that Protagoras, the father of the first of the two 'brats' (theses), is dead, so they are insulting his orphan child. Protagoras's guardians, including Theodorus, are unwilling to help, so Socrates says he must take up the cause himself and see justice done. Theodorus redirects him to Callias as guardian.
Chapter 35
What trick does Socrates describe an opponent using against the claim that seeing is knowing?
Socrates describes an adversary closing one of your eyes and asking whether you can see his cloak with the closed eye. You answer not with that eye but the other, so you see and do not see the same thing at once. The opponent refuses any 'in what sense' answer and presses the contradiction, leaving you to draw the inference.
Chapter 35
Section 364 cards
In his defense speech, how does Protagoras distinguish the disputer from the dialectician?
Protagoras says the disputer may trip up his opponent as often as he likes and make fun, but the dialectician is in earnest and only corrects his adversary when necessary, showing him the errors he fell into through his own fault or that of his company. The dialectician's aim is that the adversary blame himself, follow and love his corrector, and escape into philosophy.
Chapter 36
How does Protagoras explain the wise man if each person is a measure of what is?
Protagoras denies that wisdom has no existence. He says the wise man is one who makes the evils that appear and are to a man into goods that are and appear to him, changing a worse state into a better, as the physician works by drugs and the sophist by words. One man may still be a thousand times better than another.
Chapter 36
According to Protagoras, does a teacher ever make someone think truly instead of falsely?
No. Protagoras holds that no one can think what is not, or think anything different from what he feels, and this is always true. So no one ever made another think truly who previously thought falsely. The inferior habit of mind has kindred thoughts; a good mind causes good thoughts. What the inexperienced call true, he calls only better, not truer.
Chapter 36
What does Protagoras say about the sick man's and healthy man's perceptions of food?
Protagoras says food appears and is bitter to the sick man and the opposite to the man in health. He denies that the sick man is foolish because of one impression or the healthy man wise because of another; rather, the worse state must be changed into the better, as education changes a state and the sophist works by words like the physician by drugs.
Chapter 36
Section 373 cards
Why does Socrates insist on arguing seriously with Theodorus rather than the boys?
Socrates says that if Protagoras's wishes are to be respected, he and Theodorus must take up the argument in all seriousness and question each other. Otherwise, since the others are merely boys, they would incur the reproach of making fun with boys in their fresh analysis of Protagoras's thesis. Theodorus agrees, and also remarks that Theaetetus is better able to follow a philosophical enquiry than many long-bearded men.
Chapter 37
What self-undermining consequence does Socrates draw for Protagoras's 'man is the measure' thesis?
Socrates argues that if each person's opinion is true to that person, then when thousands judge Theodorus's opinion false, it is false for them. Since neither Protagoras nor the multitude thinks man is the measure, the thesis would be true to no one; and if the many outnumber him, his truth is proportionally more untrue than true. Protagoras thus concedes his own opinion false by admitting all opinions true.
Chapter 37
How does Socrates use common appeals to experts to refute universal equal wisdom?
Socrates asks whether people do not think themselves wiser in some things and inferior in others—looking to commanders as gods in perils of war, sea, or sickness, and seeking teachers and rulers. This implies, in their own opinion, that ignorance and wisdom exist among them, with wisdom assumed to be true thought and ignorance false opinion. Theodorus agrees, so opinions are sometimes true and sometimes false.
Chapter 37
Section 384 cards
How does Socrates contrast the philosopher's and the lawyer's use of leisure and speech?
Socrates says the philosopher always commands leisure: he talks in peace, wanders freely from subject to subject, and aims only at truth, caring not whether words are many or few. The lawyer is always hurried, driven by the clepsydra water and constrained by his adversary and the recited indictment, so he cannot expatiate at will.
Chapter 38
What does Socrates say happens to the lawyer's soul from youth upwards?
Socrates argues the lawyer is a servant, always disputing about a fellow-servant before a seated master who holds the cause, and often the race is for his life. Keen and shrewd at flattery, his soul becomes small and unrighteous; early dangers and fears drove him into crooked ways, practising deception and retaliation, so he grows stunted and warped.
Chapter 38
What does Socrates claim the 'lords of philosophy' do not know?
Socrates says they have never known the way to the Agora, dicastery, council, or any political assembly; they neither see nor hear the laws or decrees written or recited. Political clubs, banquets, revels, and singing-maidens do not enter their dreams. They know no more of city events or ancestral disgrace than how many pints the ocean holds, and are not conscious of this ignorance.
Chapter 38
What distinction does Socrates draw about Protagoras's measure doctrine regarding health and politics?
Socrates says most things and all immediate sensations, such as hot, dry, sweet, are only as they appear. But if difference of opinion is allowed at all, it must be allowed about health and disease, since not every woman, child, or creature can cure itself. Likewise in politics, Protagoras's followers will not deny that one state or counsellor is wiser about what is expedient.
Chapter 38
Section 394 cards
What jest does the Thracian handmaid make about Thales?
Socrates recounts that Thales fell into a well while looking up at the stars, and the witty Thracian handmaid joked that he was so eager to know things in heaven that he could not see what was before his feet. Socrates says this jest applies equally to all philosophers, who are unacquainted with their next-door neighbour and ignorant of what is before them.
Chapter 39
How does Socrates describe the philosopher's behavior in law-courts and public life?
Socrates says that when the philosopher must speak of things at his feet and before his eyes, in a law-court or anywhere else, he becomes a jest—tumbling into wells and disasters through inexperience. His awkwardness seems like imbecility; he has no personal scandals to answer with, is laughed at for sheepishness, and seems a downright idiot when others are praised.
Chapter 39
How does the philosopher view tyrants, large estates, and noble pedigrees?
The philosopher hears a tyrant praised and thinks of a swineherd or shepherd congratulated on milk, noting the tended creature is less tractable. Great landed proprietors seem a trifle to one accustomed to think of the whole earth. Boasting of seven generations or a pedigree back to Heracles betrays narrow vision, since everyone has thousands of ancestors, rich and poor, kings and slaves.
Chapter 39
What does Socrates say about evils and about becoming like God?
Socrates tells Theodorus that evils can never pass away, since something antagonistic to good must always remain; having no place among the gods, they hover around mortal nature. Therefore we should fly away from earth to heaven as quickly as possible, and to fly away is to become like God as far as possible—holy, just, and wise. The most righteous person is most like God.
Chapter 39
Section 403 cards
What two patterns does Socrates say are set before people?
Socrates says there are two eternal patterns: one blessed and divine, the other godless and wretched. People in their folly fail to see them and grow like one or the other through their evil deeds. The penalty is that they lead a life answering to the pattern they grow like; if they do not depart from cunning, the place of innocence will not receive them after death.
Chapter 40
How does Socrates use the fever example against Protagoras?
Socrates asks whether Protagoras extends his measure doctrine to the future. In the fever case, an ordinary man thinks heat and fever are coming while a physician thinks the contrary. Socrates asks whose opinion is likely right, or whether both are right. Theodorus calls it ludicrous, suggesting the expert's prediction about the future is the better one.
Chapter 40
What does Socrates conclude about legislation and the measure doctrine?
Socrates argues legislation aims at the good or expedient, which concerns the future, and states often fail of their highest interests. Since the wiser person better judges future outcomes, Protagoras must admit one man is wiser than another and the wiser is a measure. Socrates says he himself, who knows nothing, need not accept being a measure of anything.
Chapter 40
Section 414 cards
What two kinds of motion does Socrates distinguish?
Socrates distinguishes two kinds of motion: 'change' and 'motion in place.' Motion in place is when a thing changes from one place to another or goes round in the same place; change is when a thing remains on the same spot but grows old, turns from white to black, or from soft to hard, or undergoes any other alteration. Theodorus agrees to this distinction.
Chapter 41
How does Theodorus describe the Heraclitean sect's behavior in argument?
Theodorus says the Ephesians who profess these doctrines are 'downright mad' and impossible to converse with. They are always in motion, cannot quietly ask and answer in turn, and when questioned shoot brief, dark sayings 'as from a quiver.' If asked for a reason, they fire another new-fangled word. They refuse any settled principle, believing it would be stationary, and are 'at war with the stationary.'
Chapter 41
What does Socrates say the ancients and moderns claim about motion?
Socrates notes the ancients concealed in poetic figures the teaching that Oceanus and Tethys, origin of all things, are streams and nothing is at rest. The moderns declare openly that all is motion, so even a cobbler may learn it. Socrates also recalls the opposite doctrine of Parmenides and Melissus: 'Alone Being remains unmoved,' maintaining all being is one, self-contained, and has no place to move.
Chapter 41
How does Socrates describe the generation of qualities like heat and whiteness?
Socrates says the Heracliteans explain qualities as moving between agent and patient together with a perception. The patient ceases to be a perceiving power and becomes a percipient; the agent becomes a 'quale' instead of a quality—that is, hot and white rather than heat and whiteness. Neither agent nor patient has absolute existence; when they come together they generate sensations and their objects.
Chapter 41
Section 424 cards
What two kinds of motion do the Heraclitean supporters say all things undergo?
Theodorus agrees that things are moved in both ways distinguished earlier: they move in place and are also changed. Socrates notes that if things only moved in place without being changed, we could still state the nature of the moving things; but perfect motion requires both.
Chapter 42
Why does Socrates say the flux doctrine leaves no valid words for color or perception?
If whiteness itself is always changing into another color and never stands still, no color name can be rightly applied while the object escapes in the flux. Likewise, if all things are in motion, there is no stopping in seeing or hearing, so we cannot speak of perceiving any more than of not perceiving.
Chapter 42
What is Socrates' final verdict on Protagoras' measure doctrine and on knowledge as perception?
Socrates says they have got rid of Theodorus' friend without assenting to his doctrine that every man is the measure of all things; only a wise man is a measure. Nor can they allow that knowledge is perception, certainly not on the hypothesis of perpetual flux, unless Theaetetus can convince them otherwise.
Chapter 42
Why does Socrates hesitate to examine Parmenides' doctrine that all is one and at rest?
Socrates says he reveres Parmenides, whom he met as an old man when he was young and who seemed to have a glorious depth of mind. He fears they may not understand his words or meaning, and that the digression would thrust the main question of knowledge out of sight or overshadow it.
Chapter 42
Section 434 cards
According to Socrates, how does the soul grasp universals like being and number?
Theaetetus says universals such as being and not-being, likeness and unlikeness, sameness and difference, and number have no separate bodily organ; the mind contemplates them by a power of its own. Socrates agrees, holding that the soul views some things by herself and others through the bodily organs.
Chapter 43
What does Socrates conclude about the relation of perception to knowledge?
Socrates argues that truth and being are attained not in sense impressions but in reasoning about them. Since one who misses being cannot attain truth, and one who misses truth cannot have knowledge, perception has no part in truth or being, and so perception can never be the same as knowledge.
Chapter 43
How does Theaetetus distinguish simple sensations from reflection on them?
Socrates says simple sensations reaching the soul through the body are given by nature to humans and animals at birth, but reflection on their being and use is gained slowly and with difficulty, if ever, through education and long experience. Theaetetus agrees, and both treat this as showing knowledge lies in reasoning, not impression.
Chapter 43
What new definition of knowledge does Theaetetus offer after perception is rejected?
Theaetetus proposes that knowledge is true opinion, since not all opinion is knowledge because false opinion may exist. Socrates accepts the boldness of the answer but says he is troubled by how false opinion can arise at all, and asks whether to begin the inquiry anew.
Chapter 43
Section 444 cards
Why does Socrates claim false opinion cannot exist in the sphere of knowing?
Socrates argues all things are either known or not known, excluding learning and forgetting as irrelevant. A false opinion would require thinking what one knows to be something else one knows, or confusing known with unknown, or unknown with unknown. Each option is impossible, so false opinion is excluded from the sphere of knowing and not knowing.
Chapter 44
Why does Socrates reject defining false opinion as thinking what is not?
Socrates reasons that whoever thinks thinks some one thing, and whatever is one exists. So thinking what is not means thinking nothing, and thinking nothing is not thinking at all. Therefore no one can think what is not, whether as a self-existent substance or as a predicate, and false opinion differs from thinking what is not.
Chapter 44
What definition of false opinion does Socrates propose as heterodoxy?
Socrates suggests false opinion is a sort of heterodoxy: the mind exchanges one real object for another real object, always thinking what is, but putting one thing in place of another. Missing the aim of thought, a person substitutes base for noble or noble for base, and this is truly called false opinion.
Chapter 44
How does Socrates define thinking and opinion as silent conversation?
Socrates says thinking is the conversation the soul holds with herself, asking and answering questions, affirming and denying. When she reaches a decision and agrees without doubt, this is opinion. So forming an opinion is speaking silently to oneself, not aloud to another. He admits he scarcely understands what he speaks of.
Chapter 44
Section 454 cards
In the wax-block metaphor, what does the wax represent and how does memory work?
Socrates imagines a block of wax in the mind, varying in size, hardness, moisture, and purity between people. It is a gift of Memory, mother of the Muses. When we wish to remember something seen, heard, or thought, we press the perceptions and thoughts into the wax like a seal ring. We remember and know what is imprinted while the image lasts; when it is effaced or cannot be taken, we forget and do not know.
Chapter 45
Why does Socrates reject the earlier claim that false opinion is thinking one thing is another?
Socrates argues no one can think one thing is another whether he holds both objects in mind or only one. If he has both, he cannot say the one is the other; if only one, he would have to apprehend something not in his thoughts at all. So the view that false opinion is 'heterodoxy' (mistaking one thing for another) is nonsense, and false opinion cannot exist in that way.
Chapter 45
What is Theaetetus's proposed example of mistaking one person for another, and how does Socrates respond?
Theaetetus suggests he may know Socrates but at a distance see someone unknown to him and mistake that person for Socrates. Socrates replies that this position was already relinquished, because it involves the absurdity that we should know and not know the things we know. He then proposes to restate the assertion in another form, introducing the wax-block model to explain how deception could occur.
Chapter 45
Which cases does Socrates list as the only remaining possibilities for false opinion?
After excluding all cases involving two unknown things, two perceived things, or mismatches between knowledge, perception, and memory, Socrates says the only remaining cases are: a person may think that some things he knows, or perceives and does not know, are other things he knows and perceives; or that some things he knows and perceives are other things he knows and perceives.
Chapter 45
Section 464 cards
According to the wax block analogy, when can false opinion arise?
False opinion arises only concerning things a man knows and perceives, not things he neither knows nor has perceived. When knowing both objects and perceiving both, the mind may fail to fit the right impression of memory to the right sensation—like a bad archer missing the mark—and this misfitting is called falsehood. True opinion occurs when seals and sense impressions meet straight and opposite.
Chapter 46
What qualities of the wax make a soul wise and good at retaining knowledge?
When the wax in a soul is deep, abundant, smooth, and perfectly tempered, impressions from the senses sink in pure, clear, and lasting. Such minds easily learn and easily retain, are not liable to confusion, and quickly distribute impressions into their proper places. Socrates says these people have true thoughts and are called wise.
Chapter 46
How does Socrates characterize soft versus hard wax in the soul?
The soft are good at learning but apt to forget, since their impressions are easily confused and effaced. The hard are the reverse: they lack depth, so impressions are indistinct. Shaggy, rugged, gritty wax, or wax mixed with earth or dung, also yields indistinct impressions. The worst case is when all impressions jostle together in a little soul with no room.
Chapter 46
What does Socrates conclude about false and true opinion at the end of the passage?
Socrates and Theaetetus admit that false opinion exists in us, and true opinion also, claiming they have satisfactorily proven beyond doubt that there are these two sorts of opinion. Socrates then ironically calls himself a tiresome, garrulous creature, disheartened by his own stupidity and habit of arguing every side of a question without ever leaving off.
Chapter 46
Section 474 cards
Why does Socrates call the attempt to explain 'to know' shameless?
Socrates argues it is shameless because the entire discussion has been a search for the nature of knowledge, which they admit they do not know. Yet they keep using words like 'we know,' 'we do not know,' and 'we understand' as if they understood them. He calls this being 'infected with logical impurity'—employing terms whose meaning depends on knowledge while remaining ignorant of knowledge itself.
Chapter 47
How does Socrates distinguish 'having' knowledge from 'possessing' knowledge?
Socrates uses the example of a man who buys a garment and keeps it under control but does not wear it: we say he possesses it, not that he has it. Likewise, a man who has caught wild birds and keeps them in an aviary possesses them, yet in another sense has none of them—they are in his power and he can take any he likes whenever he pleases.
Chapter 47
What problem does the eleven-and-twelve example raise for the waxen-block theory?
Socrates asks whether someone adding five and seven in the abstract might answer eleven while another answers twelve. Theaetetus agrees many would err, and error grows with higher numbers. This implies the twelve in the waxen block is mistaken for eleven—meaning a person thinks one thing he knows to be another thing he knows, which was said to be impossible. So false opinion cannot be explained as a confusion of thought and sense.
Chapter 47
What does the aviary metaphor represent, and what is 'learning' in it?
Socrates asks Theaetetus to imagine an aviary in each person's mind containing all sorts of birds—some flocking together, some in small groups, some solitary. The birds are kinds of knowledge, and the receptacle was empty in childhood. Whenever a man gets and detains a kind of knowledge in the enclosure, he may be said to have learned or discovered the thing which is the subject of the knowledge—and this is to know.
Chapter 47
Section 484 cards
In the aviary image, what two kinds of chase after knowledge does Socrates distinguish?
Socrates distinguishes a chase prior to possession and for the sake of possession, and a chase for the sake of taking and holding what is already possessed. Thus a man who learned something long ago may resume and grasp knowledge he long possessed but did not have at hand in his mind, as when an arithmetician or grammarian sets about numbering or reading.
Chapter 48
How does Socrates use the aviary to explain false opinion?
Socrates says the various numbers and forms of knowledge fly about in the aviary. When a man wishes to capture a certain sort of knowledge from the general store but takes the wrong one by mistake, he has a false opinion—as when he thought eleven to be twelve, he got hold of the ring-dove when he wanted the pigeon. Catching the one he wants, he is not deceived.
Chapter 48
What objection does Socrates raise against the aviary explanation of false opinion?
Socrates asks how the exchange of one knowledge for another can ever become false opinion. How can a man who has knowledge of something be ignorant of it by reason of his own knowledge? It is absurd that he should suppose another thing to be this, or that knowledge present in his mind should make him ignorant—as if ignorance could make a man know or blindness make him see.
Chapter 48
What does Theaetetus propose, and how does Socrates refute it?
Theaetetus suggests there should be forms of ignorance as well as knowledge flying in the mind, so a man might catch ignorance and form a false opinion. Socrates replies that such a man would not think his opinion false; he would fancy he knows and believes he captured knowledge, not ignorance—returning them to the original difficulty.
Chapter 48
Section 494 cards
Why does Socrates argue that a justly persuaded judge lacks knowledge?
Socrates argues that judges are persuaded by report about matters knowable only by eyewitnesses. They may form a true opinion and judge rightly, but they judge without knowledge. If true opinion in law courts were the same as knowledge, the perfect judge could not have judged rightly without knowledge; therefore the two are not the same.
Chapter 49
How does the dream distinguish elements from syllables regarding knowledge?
In the dream, the primeval elements or letters have no reason or explanation and can only be named, not defined or known; they are objects of perception. Syllables or combinations of elements, being complex, are expressed by a combination of names and are known and grasped by true opinion.
Chapter 49
What definition of knowledge does Theaetetus recall from someone else?
Theaetetus recalls that true opinion combined with reason is knowledge, while opinion without reason falls outside knowledge. Things with no rational account are not knowable, and things with a reason or explanation are knowable. Socrates then tests this definition.
Chapter 49
What objection does Socrates raise against the dream's account of letters and syllables?
Socrates tests the claim that elements are unknown but combinations known, using the alphabet as a hostage. Asked to define the syllable SO, one answers S and O; but asked to define S itself, one can only call it a consonant, a mere hissing noise. Even the seven vowels have sound but no definition, so letters are truly undefined.
Chapter 49
Section 504 cards
Why does the theory that syllables are knowable but letters are not collapse?
Socrates argues that if a syllable is just all its letters, then whoever knows the syllable must know each letter, since one cannot know both together while being ignorant of either singly. So the letters would have to be known first, and the claim that syllables are knowable but letters are not is refuted.
Chapter 50
How does Socrates distinguish a whole from all?
Theaetetus initially says whole and all differ, but Socrates argues they are the same: the all is that of which nothing is wanting, and the whole likewise lacks nothing. Using number examples (six as twice three or three times two), he concludes that where a thing has parts, all the parts are both whole and all.
Chapter 50
What dilemma follows if the syllable is a single indivisible form?
If the syllable is one indivisible form with no parts, then it shares the fate of the letters: both are indefinable and unknown. But if it is a whole of many parts, then letters and syllable alike are intelligible. Either way, the claim that syllables are known while letters are not cannot stand.
Chapter 50
What earlier admission about first elements does Socrates recall?
Socrates reminds Theaetetus that they earlier agreed the first elements out of which things are compounded have no definition, since each taken alone is uncompounded. Words like 'being' or 'this' are alien and inappropriate to them, and for this reason the letters or elements were held indefinable and unknown.
Chapter 50
Section 514 cards
What three meanings of 'explanation' does Socrates distinguish?
Socrates lists three senses of rational explanation: first, manifesting one's thought through speech with verbs and nouns, like an image in a mirror or water; second, reaching the whole by enumerating its elements, as one describes a waggon by wheels, axle, body, rims and yoke; third, telling the mark or sign of difference that distinguishes a thing from all others.
Chapter 51
Why does Socrates compare letters and syllables to knowledge of elements?
Socrates argues from reading and music: learners must distinguish letters by eye and ear, and harpists must know which string answers each note, since notes are the elements of music. He concludes that simple elements are more certainly known than compounds, so anyone claiming the syllable is known while the letter is unknown is talking nonsense.
Chapter 51
How does misspelling a name show right opinion without knowledge?
Socrates notes that a learner may write 'Th' and 'e' correctly for Theaetetus but wrongly for Theodorus, showing he lacks knowledge of those first syllables. Yet when he knows the order of letters and writes them correctly, he has right opinion plus explanation—so Socrates concludes right opinion combined with explanation still falls short of knowledge.
Chapter 51
What is the third definition of explanation, and its example?
The third and popular notion is telling the mark or sign of difference that distinguishes a thing from all others. Socrates' example: the sun is the brightest of the heavenly bodies revolving about the earth. Grasping the distinguishing characteristic yields the definition, while laying hold only of what is common defines merely the things sharing that quality.
Chapter 51
Section 524 cards
What is Socrates' initial definition of knowledge involving a 'difference'?
Socrates states that whoever has right opinion about a thing and can find out the difference distinguishing it from other things will know that of which he previously had only opinion. The definition is thus right opinion plus the interpretation of the thing's distinguishing characteristic. Theaetetus agrees this account of definition is correct, before Socrates reexamines it.
Chapter 52
Why does Socrates find the definition 'unintelligible' on nearer view?
Socrates argues that when he had only opinion of Theaetetus, he had no conception of Theaetetus's distinguishing characteristics, so he must have conceived only some general nature shared with others. Mere features like nose, eyes, and mouth, or even a snub nose, cannot distinguish Theaetetus from Theodorus or a barbarian. Only a distinct impression of Theaetetus's peculiarities would allow right opinion to be recalled.
Chapter 52
What circularity does Socrates expose in adding 'definition' to right opinion?
Socrates says if the definition means forming an opinion of how something differs, the proposal is ridiculous: we are supposed to acquire right opinion of differences when we already have right opinion of them, going round and round like a rotating pestle. It is like the blind leading the blind, adding what we already have to learn what we already think. He notes the argument would only work if it said 'know' rather than 'have an opinion' of the difference.
Chapter 52
What final verdict does Socrates give about knowledge, and what does he tell Theaetetus?
Socrates concludes knowledge is neither sensation nor true opinion, nor definition and explanation added to true opinion. He compares his art to midwifery: Theaetetus has brought forth wind, and his offspring are not worth rearing. If he conceives again, the investigation will help; otherwise he will be humbler and gentler, too modest to fancy he knows what he does not. Socrates then leaves for the porch of the King Archon to meet Meletus.
Chapter 52
Source and licence
Text used: Project Gutenberg eBook #1726 (Public domain in the United States). Generated from the full text; cards paraphrase the source.
Version: Public domain edition. Retrieved 2026-10-28. Cards reviewed 2026-10-28.
These cards paraphrase the text for study. They are not a substitute for reading the book, and they do not reproduce long passages.
Turn your own notes into cards
Upload a PDF, Word, or text file and get question-and-answer cards for closed-notes practice. Five cards are free, no signup.