Encyclopedia of Philosophy: The Theaetetus and the Sophist of Plato

« channels through which we see colours and hear sounds.

The objects of one sense cannot be perceived withanother: we cannot hear colours or see sounds.

But in that case, the thought that a sound and a colour are notthe same as each other, but two different things, cannot be the product of either sight or hearing.

Theaetetus hasto concede that there are no organs for perceiving sameness and difference or unity and multiplicity; the mind itselfcontemplates the common terms which apply to everything.

But the truth about the most tangible bodily propertiescan only be reached by the use of these common terms, which belong not to the senses but to the mind.Knowledge resides not in the sense-impressions but in the mind's reflection upon them.At last Theaetetus gives up the thesis that knowledge is perception: he proposes instead that it consists in thejudgements of the reflecting mind.

Socrates approves of this change of course.

When the mind is thinking, he says,it is as if it were talking to itself, asking questions and answering them, saying yes or no.

When it concludes its internaldiscussion with itself, and comes out silently with its answer, that is a judgement.Knowledge cannot be identified outright with judgement, because there is such a thing as false judgement as wellas true judgement.

It is not easy to give an account of false judgement: how can I make the judgement that A = Bunless I know what A is and what B is, and if I know that, how can I get the judgement wrong? The possibility offalse judgement seems to threaten us with having to admit that someone can know and not know the same thing atthe same time.Let us suppose, Socrates now suggests, that the mind is a wax tablet.

When we want to commit something tomemory we stamp an impression or an idea on this tablet, and so long as the stamp remains we remember.

Falsejudgement may occur in the following way.

Socrates knows Theaetetus and his tutor Theodorus and he has imagesof each of them stamped on the tablet of his memory; but seeing Theaetetus at a distance, he mistakenly matcheshim not to his own image, but to the image of Theodorus.

The more indistinct the images on the wax become, themore possible it is that such mistakes are made.

False judgement, then, comes about through a mismatch betweenperception and thought.But are there not cases where we make false judgements when no perception is in question: when we make amistake in working out a sum in arithmetic, for instance? In order to take account of these cases, Socrates saysthat it is possible to possess knowledge without holding it in your mind on a particular occasion, just as you canpossess a coat without wearing it.

Think of the mind now not as a waxen tablet, but as an aviary.

We are born witha mind which is an empty cage; as we learn new things we capture new birds, and knowing something is having thecorresponding bird in our collection.

But if you want to make use of a piece of knowledge, you have to catch theappropriate bird and hold him in your hand before letting him go again.

Thus we explain mistakes in arithmetic:someone who knows no arithmetic has no number birds in his aviary; a person who judges that 7 + 5 = 11 has allthe right birds fluttering around, but catches the eleventh bird instead of the twelfth bird.Whether or not these similes are sufficient to make clear the nature of false judgement, there is a difficulty,Socrates points out, with the thesis that knowledge is true judgement.

If a jury is persuaded by a clever attorneyto bring in a certain verdict, then even though the verdict accords with the facts, the jurors do not have theknowledge that an eye-witness would have.

Theaetetus then modifies his definition so that knowledge is ajudgement or belief which is not only true but articulate.Socrates then explores three different ways in which a belief about something might be said to be articulate.

Mostobviously, someone has an articulate belief if he can express it in words; but anyone with a true belief who is notdeaf and dumb can do this, so it can hardly make the difference between true belief and knowledge. The second way is the one which Socrates takes most seriously: to have an articulate belief about an object is tobe able to offer an analysis of it.

Knowledge of a thing is acquired by reducing it to its elements.

But in that casethere can be no knowledge of any of the ultimate, unanalysable elements.

The elements which make up thesubstances of the world are like the letters which make up the words in a language, and analysing a substance maybe compared with spelling a word.

But while one can spell ‘Socrates' one cannot spell the letter ‘S'.

Just as a lettercannot be spelt, the elements of the world cannot be analysed and therefore cannot be known.

But if the elementscannot be known, how can complexes made out of them be known? Moreover, while knowledge of elements may benecessary if we are to have knowledge of complexes, it is not sufficient; a child might know all his letters, and yetnot be able to spell consistently.On the third interpretation someone has an articulate belief about an object if he can spell out a description whichis uniquely true of it.

Thus, the sun may be described as the brightest of the heavenly bodies.

But on this view,how can one have any idea at all of something without having an articulate belief about it? I cannot really bethinking of Theaetetus himself if the only things I can say in description of him are things he has in common withothers, like having a nose and eyes and a mouth.Socrates concludes, a little precipitately, that Theaetetus' third definition of knowledge is no better than his twoprevious ones.

The dialogue ends in bafflement, like the Socratic dialogues of Plato's early period.

But in fact, it hasachieved a great deal.

The account which it gives of the nature of sense-perception, modified by Aristotle, becamestandard until late in the Middle Ages.

The definition of knowledge as articulate true belief, interpreted as meaningjustified true belief, was still accepted by many philosophers in the present century.

But what Plato probably saw asthe dialogue's greatest achievement was the cure which it provided for the scepticism of Heraclitus, by showingthat the doctrine of universal flux was self-refuting.In the Theaetetus Socrates expresses himself too much in awe to take on in argument the philosopher who standsat the opposite extreme from Heraclitus, the venerable Parmenides.

This task Plato undertakes in the dialogue TheSophist.

In this dialogue, though Theaetetus and Socrates reappear, the chief speaker is not Socrates, but astranger from Parmenides' town of Elea.

The ostensible purpose of the dialogue is to provide a definition of thesophist.

The definition is pursued by the method popular in our own day in the game of Twenty Questions.

In that. »