The Theaetetus is one of Plato’s more famous dialogues. According to experts, it dates from Plato’s late period of writing and it fits in with his Republic. But there are important differences between both works.
In the Republic, Plato expounds his famous theory of Forms. According to him, knowledge consists in understanding the Forms – using the mind’s eye, so to speak – which are intelligible but insensible. In other words, our senses lead to opinion, not to knowledge, while only reasoning can show us the true objects.
But in the Theaetetus, Plato seems to forget all about his earlier theory of Forms and he turns sceptical when it comes to knowledge. In short: after refuting various conceptions of knowledge, Plato and his conversational partner, Theaetetus, come to the conclusion that it is impossible to define what knowledge is. But Theaetetus leaves the dialogue with the fine remark of Plato that at least he now knows that he doesn’t know anything.
The dialogue is at times hard to follow, but not impossible to understand. And many times in Theaetetus Plato is able to interrupt the current dense dialogue with funny interludes.
In essence, Plato discusses (through Socrates) three conceptions of knowledge, which he eats refutes.
1. Knowledge is perception.
2. Knowledge is true judgement.
3. Knowledge is true judgement with an account given of it.
In the first half of the dialogue, Plato deals with the conception of knowledge as perception. In doing so, he deals with Heraclitus’ theory of flux (i.e. change) and Protagoras’ relativism.
Heraclitus’ flux theory of the world is, by definition, impossible as knowledge. If everything is continuously in change (something Heraclitus never claimed, but alas), it is impossible to arrive at a reliable description of things. Describing things in the world requires a certain stability in spacetime, since it is only by convention that words resemble objects – if objects continuously come and go, there’s no resemblance to obtain. To me, this seems to be a straw-man, since Heraclitus never claimed everything is flux, he actually claimed behind all the apparent flux there’s a stable reality, only to be known through the intellect. So in this sense, Heraclitus actually should be seen as a precursor to Plato’s own theory of knowledge.
Protagoras’ relativism says that ‘man is the measure of all things’, which leads to a subjectivist view on reality. If each person senses and perceives the world from his/her own perspective; and each person has his/her own intellect; then each person knows the world. This leads to as many true judgements as there are subjects perceiving the world, and even to the different true judgements for the same subject at different times. A claim bishop Berkeley would make in the eighteenth century (Berkeley founded his subjectivism in God’s perfection – since God perceives everything instantaneously, there is a Being perceiving the World – offering a stop to extreme relativism. Of course, everything now hinges on the existence of this Being, which itself is problematic).
Plato rightfully asks the simple question: why is not a buffoon the measure of all things? Or a tadpole? But more seriously, if everyone has true beliefs based on his/her own perceptions, there are many contradicting judgements out there. This is logically impossible: a judgement is either true or not. If person A beliefs a judgement to be true and person B beliefs the same judgement to be false, there is a contradiction. And contradiction is the criterion with which we judge the truth of a proposition – a proposition that contradicts itself cannot be true. So if Protagoras claims all judgements are true, and I claim this proposition is false, there’s a problem.
Plato then proceeds to show how the existence of experts refutes Protagoras’ position. If all beliefs are true, why do we need experts? Why do we need Protagoras as a rhetorician if we all can know the truth simply by perceiving? We rely on experts precisely because they have – on average – more true beliefs about a subject than we, as laypeople, do. He concludes the section by refuting Theaetetus’ original claim that knowledge is perception – perception is mere experiencing sense-data. It is entirely possible to know something without perceiving it, or to perceive something without knowing it.
So, Plato takes on the second conception of knowledge: knowledge is true judgement. But, as he lets Socrates exclaim at the end of this piece of dialogue, it is entirely possible to make a true judgement without knowing about it – if I claim the whole day that it’s 3:15, I still am right twice a day. It doesn’t mean I know what I’m talking about.
Socrates has two analogies of making true judgements, which both leave much to be questioned. First, he uses the analogy of a wax tablet. Our mind is a wax tablet and perceptions leave imprints on it – this is what we call memory. Then, when we perceive something and associate it with the correct memory, it is a true judgement. When we associate the current perception with a wrong memory, this is false belief. But this misidentification-theory of knowledge doesn’t work well, so Socrates offers a second analogy: the mind as an aviary.
Possessing knowledge is like possessing birds – only by putting them in a cage do we possess them. Grasping something (i.e. catching birds) isn’t the same as possessing something (i.e. possessing birds). The birds fly in the aviary, along with birds we didn’t know were in the aviary, and when we make judgements we either pick the right (known) bird or the wrong (unknown or another) bird. In the first instance, we make a true proposition, while in the second instance, we make a false proposition. This doesn’t tell us – at all – how the birds (known and unknown) got in the cage to begin with. A problem later philosophers, like John Locke and David Hume, would seize upon and offer their own theories of knowledge. In short, Plato claims ‘knowledge is true judgement’ is false but he doesn’t offer a satisfying answer to the problem.
The last part of the dialogue sees Socrates defending the claim that ‘knowledge is true belief with an account’. This, in short, means that in order to count as knowledge, something has to be a true belief and it has to be able to be communicated in words (i.e. logos). Socrates here offers a third analogy, that of the dream (known as ‘Socrates’ Dream’). According to this, knowledge consists in defining objects in terms of their parts. But this is problematic, since how do we define the parts? According to Socrates, the parts are unknowable, but the wholes (build from these parts) are knowable.
So Socrates attacks this conception of knowledge on the point that it is unsatisfying (or impossible?) to know something that consists of unknowable parts – that is, if knowledge presupposes communication (logos). The dialogue ends with a dilemma: if knowledge consists in distinguishing things from other things (which, if not the case, would mean all things are the same), then does knowledge consist in judging the crucial distinction of a thing? But if this is so, then everyone who perceives and consequently judges A differs from B knows A. Which brings the problem of reliability and expertise (cf. Plato’s attack on Protagoras) back full-circle. Or else, does knowledge consist of knowing which quality distinguishes A from B? But this, then, presupposes knowing, which is the thing Plato set out to prove from the beginning (i.e. begging the question).
This problem leads Socrates to conclude that it’s impossible to define knowledge, at least as perception or as true judgement (with or without further conditions). And now the young Theaetetus, although still not knowing what knowledge is, at least knows what it’s not. And this is as much as we can hope for, according to Socrates, at least.
A pressing question at this point would be: is it possible to know something without being able to define what knowing is? And does existence preclude knowledge? In short: is this not simply a pseudo-problem, although a supposedly important one? One can see the problem in modern-day science – ever since the nineteenth century, science broke away from philosophy and just went on discovering all kinds of things. Nowadays, there’s no scientist who uses or needs to use philosophy to gather knowledge. This is pragmatism in full force: true is that which is the most useful to explain the data and to manipulate nature. It’s not for nothing that the early twentieth century, the most recent era with the biggest scientific breakthroughs, led to new ways of tackling the old philosophical chestnut of knowledge. Logical-positivism, falsificationism, paradigm-shift-theories, etc. are all philosophical attempts to circumvent Plato’s problem of defining knowledge.
Anyway, the Theaetetus is an interesting read, although at times a bit abstract. Being familiar with Pre-Socratic ideas (especially Protagoras, Heraclitus and Empedocles) can be helpful, as well as being familiar with some of Plato’s other views of knowledge (e.g. his theories as outlined in Republic and Phaedo). It’s still unclear to me how Plato’s different conceptions of knowledge connect with one another – did he think his theory of Forms is true? Did he conclude there’s no theory of knowledge possible? I guess we’ll never know.