The Theaetetus of Plato Book

Epistemological Idiots

Here Plato engages with the concept of ‘knowledge’ and ‘understanding’ as in many other dialogues, but Theaetetus is often hailed as ‘Plato’s most sustained study of epistemology,’ and is a deep investigation into the question ‘What is knowledge?’ As such, it is the founding document of what has come to be known as ‘epistemology’, as one of the most important branches of philosophy and went on to influence Aristotle, the Stoics and the modern geography of the field.

In comparison with most Platonic Dialogues, Theaetetus is a complex and difficult work of abstract philosophical theory and attempting to summarize would only serve to make it even more so. The difficult topic of epistemology and its many twists and turns are best left to Socrates’ expert hands. Here I will only try to outline my understanding of how this dialogue fits into Plato’s overall objectives.

Socrates’ abiding passion was the question of practical conduct, and to be able to have any workable theory on conduct and the ‘good life’, it is not acceptable that truth is relative — if there is no stable norm, no abiding object of knowledge, Socrates (and thus Plato’s) basic objective collapses. This is why it was essential to be convinced that ethical conduct must be founded on knowledge, and that that knowledge must be knowledge of eternal values which are not subject to the shifting and changing impressions of sense or of subjective opinion, but are the same for all men and for all peoples and all ages, eternal.

This conviction that there can be knowledge in the sense of objective and universally valid knowledge is what animates the spirit of Theaetetus — to demonstrate this fact theoretically, and to probe deeply into the problems of knowledge, asking what knowledge is and of what.

Keeping with this objective, in the Theaetetus Plato's first object is the refutation of false theories. Accordingly he sets himself the task of challenging the theory of Protagoras that knowledge is perception, that what appears to an individual to be true is true for that individual. His method is to elicit dialectically a clear statement of the theory of knowledge implied by the the epistemology of Protagoras, to exhibit its consequences and to show that the conception of "knowledge" thus attained does not fulfill the requirements of true knowledge at all, since knowledge must be, Plato assumes, (i) infallible, and (ii) of what is.

Sense-perception is knowledge fails spectacularly (and quite satisfactorily for Plato) in this examination as it is neither the one nor the other. Sense-perception is not, therefore, worthy of the name of knowledge. It should be noted how much Plato is influenced by the conviction that sense-objects are not proper objects of knowledge and cannot be so, since knowledge is of what is, of the stable and abiding, whereas objects of sense cannot really be said to be but only to become.

This first of Theaetetus’ (Theaetetus was a famous mathematician, Plato’s associate for many years in the Academy) three successive definitions of knowledge — that knowledge is simply ‘perception’ — is not finally ‘brought to birth’ until Socrates has linked it to Protagoras’ famous ‘man is the measure’ doctrine of relativistic truth, and also to the theory that ‘all is motion and change’ that Socrates finds most Greek thinkers of the past had accepted, and until he has fitted it out with an elaborate and ingenious theory of perception and how it works. He then examines separately the truth of these linked doctrines and, in finally rejecting Theaetetus’ idea as unsound, he advances his own positive analysis of perception and its role in knowledge:

Thus Socrates proceeds to the next two definitions of knowledge — that ‘Knowledge is simply "True Judgment”’ and that ‘Knowledge is True Judgment plus an "Account" of it.’ After systematic exploration of these ideas (with a few amusing digressions) and rejecting them as unsound Socrates paves the way toward an acceptable theory of Forms, to be explored further in dialogues such as Parmenides and The Republic .

Epistemological Idiots? Not Quite.

Once we reject the three proposals and reach the aporetic conclusion of the dialogue, our first impulse might be, as with all epistemological explorations, to conclude that Socrates has proved that it is impossible to define ‘what is knowledge’ and hence, by extension, the impossibility of knowledge itself. I almost laughed with triumph at this nihilistic ending until I was put in my place by reading commentaries on the subject. For a quick flavor:
SOCRATES: And so, Theaetetus, if ever in the future you should attempt to conceive or should succeed in conceiving other theories, they will be better ones as the result of this inquiry. And if you remain barren, your companions will find you gentler and less tiresome; you will be modest and not think you know what you don’t know. This is all my art can achieve — nothing more.
Instead, a more nuanced reading of Theaetetus’ conclusion by situating it among the Platonic corpus will tell us that the conclusion to be drawn is not that no knowledge is attainable through definition, but rather that the individual, sensible object is indefinable and is not really the proper object of knowledge at all. The object of true knowledge must be stable and abiding, fixed, capable of being grasped in clear and scientific definition, which is of the universal, as Socrates saw. In the Theaetetus he shows that neither sense-perception nor true belief are possessed of both these requirements; neither, then, can be equated with true knowledge.

This is the real conclusion of the dialogue, namely, that true knowledge of sensible objects is unattainable, and, by implication, that true knowledge must be knowledge of the universal and abiding, which must be, as we have said, (i) infallible, (ii) of what is.

The key to understanding Theaetetus is to accept that Plato has assumed from the outset that knowledge is attainable, and that knowledge must be (i) infallible and (ii) of the real. True knowledge must possess both these characteristics, and any state of mind that cannot vindicate its claim to both these characteristics cannot be true knowledge. It follows, then, that it is the universal and not the particular that fulfills the requirements for being an object of knowledge. Knowledge of the highest universal (beauty, goodness, justice, courage, etc.) will be the highest kind of knowledge, while "knowledge" of the particular will be the lowest kind of "knowledge." This connects us directly to the famous line analogy of The Republic and paves the way for The Theory of Forms.

Theaetetus is a valuable but difficult dialogue to be familiar with since Plato explores epistemology without letting on his intentions and this might prove difficult to readers who treat this dialogue as standing by itself. Instead it needs to be treated as part of a continuum, that started with Parmenides and is carried forward in The Sophist and The Statesman (the next two parts of the ‘trilogy’) and on to The Republic, destined to trouble Plato for the rest of his career, never being resolved satisfactorily enough.