39 pages • 1 hour read
PlatoTheaetetus
Nonfiction | Book | AdultA modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 8-15Chapter Summaries & Analyses
Chapter 8 Summary: “Dice and Size Puzzles”
Socrates presents an initial puzzle regarding the theory that knowledge is perception. He uses the example of size. If a young man grows in one year while an old man does not, then it is possible that the latter becomes shorter than the former. If this is the case, then it seems, according to the theory that knowledge is perception, that two contradictory things must be true. First, that nothing about the old man has changed. Second, that at least one fact about him has changed, that he is now shorter than the young man. Socrates says that “more subtle” adherents of the perception theory of knowledge might try to avoid this objection by appealing to a certain metaphysical theory. Namely, they do so by arguing that everything in the universe is in a state of change.
Chapter 9 Summary: “Theory of Perception”
Socrates discusses the idea that everything changes in more detail. He explains how change and motion give rise to perception. That is, an object’s motion interacts with the change in the sense organ, such as the eye. This produces the impression of, for example, a white piece of wood. Furthermore, if true, this would help resolve a problem for the perception theory of knowledge: how the same thing appears differently to different people at different times. This is because it would never quite be the same object interacting in quite the same way with the perceiver, and so would be perceived differently.
Chapter 10 Summary: “Dreaming”
Another problem with the perception theory of knowledge is misperception. Namely, how can this theory account for cases when people seem to “mis-hear or miss-see or miss-perceive” (27)? Socrates draws on dreaming to expand on this. As he says, “what evidence would one be able to point to, if someone asked at this very moment whether we’re asleep and dreaming everything that we have in mind, or awake?” (27). In other words, there are states, like dreaming or madness, when our perceptions do not correspond with reality. Yet perception itself seems to provide no way of differentiating between those states and veridical ones.
Chapter 11 Summary: “Perceptual Agents and Patients”
Those who still wish to defend the perception theory of knowledge therefore appeal to another argument to respond to the objection raised in Chapter 10. Socrates cites the distinction between health and sickness to reconstruct this point. If one is healthy, then a wine will taste sweet, whereas the same wine when one is sick will taste bitter. What he infers from this is that knowledge is still accurate perception of an object if we can appeal to a third party who can establish what state we are in. In that case, the bitter wine is still a truthful perception of the wine, if we understand it is wine for a sick person. Likewise, perceptions in dreams should not be treated as false. Rather, they represent knowledge relative to a dreaming state, which can be established by another person who observes whether we are asleep or awake.
Chapter 12 Summary: “Protagoras Criticized”
Socrates moves on to discuss another criticism of the perceptual theory of knowledge espoused by Protagoras. He asks why Protagoras did not say that “the measure of all things is a pig, or a baboon, or some other creature that has perception” (33), rather than just man. In other words, an apparent consequence of Protagoras’s theory is that it grants sentient animals, such as pigs or baboons, as much knowledge as humans. Likewise, it suggests that among humans, all perceivers are equal and thus no one can claim to be wiser than another.
Chapter 13 Summary: “Knowledge Is Perception Criticized”
Socrates attacks Protagoras by pointing to a second absurd consequence that allegedly follows from identifying knowledge with perception. This is connected to memory. As he says to Theaetetus, if we perceive something then remember it, we would surely want to claim that we had knowledge of that thing. Yet the perceptual theory of knowledge seems to deny that. This is because “one can fail to know something of which one has come to have knowledge, while one still remembers it—because one doesn’t see it” (37). In short, Protagoras’s theory appears committed to the view that memories of perceptions are not knowledge because they are not directly perceived.
Chapter 14 Summary: “Further Criticisms”
In a further criticism of Protagoras, Socrates highlights the example of covering one eye with a hand while leaving the other uncovered. In this instance, he argues, it seems as if we are both perceiving and not perceiving. Yet if knowledge is perception, then this means that we both must know and not know the object. Theaetetus agrees that this conclusion is absurd.
Chapter 15 Summary: “Defence of Protagoras”
Socrates imagines how Protagoras, or one of his defenders, might respond to the earlier objections. Protagoras might hypothetically say that the theory that knowledge is perception, and thus that all perception is true, does not rule out the possibility that one person might be wiser than another. This is because in wisdom, what is aimed at is not what is true. Rather, what is sought is what is better. In this way the wise man sees things in a more beneficial and healthy way than the unwise man. It also follows from this that wisdom and learning, under Protagoras’s theory, are still worth pursuing.
Chapters 8-15 Analysis
that knowledge is perception, Socrates explores several objections and responses to this theory. This helps the reader better understand the Socratic method. It is not just that Socrates poses questions to establish aporia but that this questioning proceeds in a specific way, in a dialectic. That is, the progressively deepening of understanding of a position through back-and-forth questioning and response. Further, Socrates’s role in this is not that of a teacher pushing a student down a road of prepared answers and responses. Rather, he seeks to elicit original thought and argument. This is what Socrates means when he says of his interlocutors, “I know no more than he does, apart from a tiny bit, enough to be able to get an argument from someone else” (32).
Nevertheless, some of the arguments he constructs with Theaetetus seem weak. One of these is the argument about partial perception, which uses the hypothetical that a man “covers one of your eyes with his hand, and asks if you see his coat with the one that’s covered” (39). Since the answer is that we both see and do not see at the same time, an absurdity, it is inferred that knowledge cannot be perception. Yet this is easily countered. A more sophisticated version of the perceptual theory of knowledge could merely say that to know means to perceive a gestalt or whole present to the mind. Knowing does not have to mean perceiving with specific senses. Likewise, the criticism that a perceptual theory of knowledge would deny that the memory of a perception is not knowledge is limited. A more nuanced perceptual theory could accommodate this simply by accepting that recollections of past events count as forms of perception.
There are stronger objections. One of these focuses on the issue of misperceptions or false perceptions. As Rene Descartes also highlighted in his Meditations on First Philosophy (1641), a perceptual theory of knowledge struggles to make sense either of optical illusions or hallucinations. If a branch in a river appears bent, does this mean it is bent, even though closer inspection will reveal it to be straight? Socrates employs a more generalized version of this worry in looking at the case of dreams and madness. He asks how we can know that we are not systematically mistaken about all our perceptions if our only recourse is perception itself. Indeed, as with hallucinations, it seems a strict perceptual theory of knowledge struggles to say when we are dreaming and waking and to distinguish between dreaming and waking.
However, Socrates does not linger on this problem. Instead, he focuses on the question of wisdom, developing an objection that will play a key role in later chapters. Namely, of Protagoras’s theory, he asks, how can we say that any person is wiser than another if all knowledge is relative to our perceptions? In Chapter 13 Socrates uses the example of foreign languages to highlight this point. Everyone can hear a foreign language in terms of the sounds made, but can we seriously say that a native speaker and a novice speaker know the language equally?
At its most general, the response Socrates imagines from Protagoras is a pragmatic one. It sidesteps the question of knowledge and wisdom by arguing that wisdom resides in what is useful. For instance, “wise and good politicians make beneficial things instead of harmful ones” (42). One politician is wiser than another, then, to the extent that their actions result in greater or lesser utility. Moreover, this standard of benefit is judged by the people of a state themselves. As Socrates says, paraphrasing this point, “if any sort of thing seems just and admirable to any state, then it actually is just and admirable for it, as long as that state accepts it” (42). This temporarily parries the wisdom objection. However, it raises problems of its own. How far does it work outside the world of politics, where there is no common judgment to appeal to? And what happens if the alleged utility of different actions is contested or appears differently at different times? These are issues Socrates explores in subsequent chapters. In the process he hopes to land a knockout blow against the Protagorean theory of knowledge.
Related Titles
By Plato
