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Encyclopedia of Philosophy: THE THEORY OF IDEAS of PLATO

Publié le 09/01/2010

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Plato’s theory arises as follows. Socrates, Simmias, and Cebes are all called ‘men’; they have it in common that they are all men. Now when we say ‘Simmias is a man’ does the word ‘man’ stand for something in the way that the word ‘Simmias’ stands for the individual man Simmias? If so, what? Is it the same thing as the word ‘man’ stands for in the sentence ‘Cebes is a man’? Plato’s answer is yes: in each case in which such an expression occurs it stands for the same thing, namely, that which makes Simmias, Cebes, and Socrates all men. This is given by Plato various designations, Greek phrases corresponding for instance to ‘the man himself’, or ‘that very thing which is man’. Because, in calling Socrates a man, Plato    meant not that he was male, but that he was human, the common thing meant by ‘man’ can be called – by analogy with Plato’s use in other cases – ‘humanity’. But its best known designation is ‘The Idea (or Form) of Man’.  Generalizing, in any case where A,B,C, are all F, Plato is likely to say that they are related to a single Idea of F. Sometimes he states the principle universally, sometimes, in particular cases, he hesitates about applying it. In various places he lists Ideas of many different types, such as the Idea of Good, the Idea of Bad, the Idea of Circle, the Idea of Being, the Idea of Sameness. And as long as he held the theory at all Plato seems to have continued to believe in the Ideas of Good and Beauty and Being. But he seems to have been unsure whether there was an Idea of Mud.

« and that only a concrete individual can be a human being? (D) Classes.

Attributes serve as principles according to which objects can be collected into classes: objects whichpossess the attribute of humanity, for instance, can be grouped into the class of human beings.

In some waysclasses seem closer than attributes to Platonic Ideas: participation in an Idea can be understood without too muchdifficulty as membership of a class.

Classes, like attributes, and unlike paradigms and concrete universals, resembleIdeas in their abstract properties.

However, there is an important difference between attributes and classes.

Twoclasses with the same members (the same extension, as philosophers sometimes say) are identical with each other,whereas attribute A need not be identical with attribute B even though all and only those who possess A possessalso B.

Being a human, for instance, is not the same attribute as being a featherless biped, though the class offeatherless bipeds may well be the same class as the class of human beings.

Philosophers express this difference bysaying that classes are extensional, while attributes are not.

It is not clear whether Plato's Ideas are extensionallike classes, or non-extensional like attributes.

The difficulty in identifying Ideas with classes arises over theses (2)and (3).

The class of men is not a man and we cannot say in general that the class of Fs is F; some classes aremembers of themselves and some are not.

There are problems in this area which only became fully obvious morethan two millennia later.Concepts such as those of attribute and class are more or less sophisticated descendants of Plato's notion; none ofthem, however, does justice to the many facets of his Ideas.

If one wants to see how the theses (1) to (5)seemed plausible to Plato, it is better to take, not any modern logician's technical concept, but some moreunreflective notion.

Consider one of the points of the compass, North, South, West, and East.

Take the notion ofthe East, for instance, not as one might try to explain it in virtue of an abstract notion, e.g.

eastwardness, but asone might conceive it by naive reflection on the various locutions we in Britain use about the East.

There are manyplaces which are east of us, e.g.

Belgrade, Warsaw, and Hong Kong.

Anything which is thus east is in the East, isindeed a part of The East (participation); or, if you prefer, it is in more or less the same direction as The East(imitation).

It is by virtue of being in The East, or by virtue of being in the same direction as that point of thecompass, that whatever is east of us is east (Thesis 1).

Now The East cannot be identified with any of the placeswhich are east of us: it is provincial to think that ‘The East' means a place such as India, since from some otherpoint of view, e.g.

that of Beijing, India is part of The West (Thesis 2).

The East itself, of course, is east of us – towalk towards The East you must walk eastwards – and The East is nothing but east; we may say ‘The East is red'but we really mean that the eastern sky is red (Thesis 3).

Nothing but The East is unqualifiedly east: the sun issometimes east and sometimes west, India is east of Iran but west of Vietnam, but in every time and every placeThe East is east (Thesis 4).

Moreover, The East cannot be identified with any point in space, nor has it any historyin time, nor can it be seen, handled, or parcelled out (Thesis 5). I am not, of course, suggesting that points of the compass will supply an interpretation of Plato's Ideas which willmake all theses (1) to (5) come out true.

No interpretation could do this since the theses are not all compatiblewith each other.

I am merely saying that this interpretation will make the theses look prima facie plausible in a wayin which the interpretations previously considered will not.

Concrete universals, paradigms, attributes, and classesall raise problems of their own, as philosophers long after Plato discovered, and though we cannot go back to Plato'ssolutions, we have yet to answer many of his problems in this area.. »

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