History of Western Philosophy - Bertrand Russell [73]
The following paragraphs summarize Plato's theory of ideas.
Our question is: What is a philosopher? The first answer is in accordance with the etymology: a philosopher is a lover of wisdom. But this is not the same thing as a lover of knowledge, in the sense in which an inquisitive man may be said to love knowledge; vulgar curiosity does not make a philosopher. The definition is therefore amended: the philosopher is a man who loves the 'vision of truth'. But what is this vision?
Consider a man who loves beautiful things, who makes a point of being present at new tragedies, seeing new pictures, and hearing new music. Such a man is not a philosopher, because he loves only beautiful things, whereas the philosopher loves beauty in itself. The man who only loves beautiful things is dreaming, whereas the man who knows absolute beauty is wide awake. The former has only opinion; the latter has knowledge.
What is the difference between 'knowledge' and 'opinion'? The man who has knowledge has knowledge of something, that is to say, of something that exists, for what does not exist is nothing. (This is reminiscent of Parmenides.) Thus knowledge is infallible, since it is logically impossible for it to be mistaken. But opinion can be mistaken. How can this be? Opinion cannot be of what is not, for that is impossible; nor of what is, for then it would be knowledge. Therefore opinion must be of what both is and is not.
But how is this possible? The answer is that particular things always partake of opposite characters: what is beautiful is also, in some respects, ugly; what is just is, in some respects, unjust; and so on. All particular sensible objects, so Plato contends, have this contradictory character; they are thus intermediate between being and not-being, and are suitable as objects of opinion, but not of knowledge. 'But those who see the absolute and eternal and immutable may be said to know, and not to have opinion only.'
Thus we arrive at the conclusion that opinion is of the world presented to the senses, whereas knowledge is of a super-sensible eternal world; for instance, opinion is concerned with particular beautiful things, but knowledge is concerned with beauty in itself.
The only argument advanced is that it is self-contradictory to suppose that a thing can be both beautiful and not beautiful, or both just and not just, and that nevertheless particular things seem to combine such contradictory characters. Therefore particular things are not real. Heraclitus had said 'We step and do not step into the same rivers; we are and are not.' But combining this with Parmenides we arrive at Plato's result.
There is, however, something of great importance in Plato's doctrine which is not traceable to his predecessors, and that is the theory of 'ideas' or 'forms'. This theory is partly logical, partly metaphysical. The logical part has to do with the meaning of general words. There are many individual animals of whom we can truly say 'this is a cat'. What do we mean by the word 'cat'? Obviously something different from each particular cat. An animal is a cat, it would seem, because it participates in a general nature common to all cats. Language cannot get on without general words such as 'cat', and such words are evidently not meaningless. But if the word 'cat' means anything, it means something which is not this or that cat, but some kind of universal cattiness. This is not born when a particular cat is born, and does not die when it dies, In fact, it has no position in space or time; it is 'eternal'. This is the logical part of the doctrine. The arguments in its favour, whether ultimately valid or not, are strong, and quite independent of the metaphysical part of the doctrine.
According to the metaphysical part of the doctrine, the word 'cat' means a certain ideal cat, 'the cat', created by God, and unique. Particular cats partake of the nature of the cat, but more or less imperfectly;