History of Western Philosophy - Bertrand Russell [119]
What, exactly is meant by the word 'category', whether in Aristotle or in Kant and Hegel, I must confess that I have never been able to understand. I do not myself believe that the term 'category' is in any way useful in philosophy, as representing any clear idea. There are, in Aristotle, ten categories: substance, quantity, quality, relation, place, time, position, state, action, and affection. The only definition offered of the term 'category' is: 'expressions which are in no way composite signify'—and then follows the above list. This seems to mean that every word of which the meaning is not compounded of the meanings of other words signifies a substance or a quantity or etc. There is no suggestion of any principle on which the list of ten categories has been compiled.
'Substance' is primarily what is not predicable of a subject nor present in a subject. A thing is said to be 'present in a subject' when, though not a part of the subject, it cannot exist without the subject. The instances given are a piece of grammatical knowledge which is present in a mind, and a certain whiteness which may be present in a body. A substance in the above primary sense is an individual thing or person or animal. But in a secondary sense a species or a genus—e.g. 'man' or 'animal'—may be called a substance. This secondary sense seems indefensible, and opened the door, in later writers, to much bad metaphysics.
The Posterior Analytics is a work largely concerned with a question which must trouble any deductive theory, namely: How are first premisses obtained? Since deduction must start from somewhere, we must begin with something unproved, which must be known otherwise than by demonstration. I shall not give Aristotle's theory in detail, since it depends upon the notion of essence. A definition, he says, is a statement of a thing's essential nature. The notion of essence is an intimate part of every philosophy subsequent to Aristotle, until we come to modern times. It is, in my opinion, a hopelessly muddle-headed notion, but its historical importance requires us to say something about it.
The 'essence' of a thing appears to have meant 'those of its properties which it cannot change without losing its identity'. Socrates may be sometimes happy, sometimes sad; sometimes well, sometimes ill. Since he can change these properties without ceasing to be Socrates, they are no part of his essence. But it is supposed to be of the essence of Socrates that he is a man, though a Pythagorean, who believes in transmigration, will not admit this. In fact, the question of 'essence' is one as to the use of words. We apply the same name, on different occasions, to somewhat different occurrences, which we regard as manifestations of a single 'thing' or 'person'. In fact, however, this is only a verbal convenience. The 'essence' of Socrates thus consists of those properties in the absence of which we should not use the name 'Socrates'. The question is purely linguistic: a word may have an essence, but a thing cannot.
The conception of 'substance', like that of 'essence', is a transference to metaphysics of what is only a linguistic convenience. We find it convenient, in describing the world, to describe a certain number of occurrences as events in the life of 'Socrates', and a certain number of others as events in the life of 'Mr Smith'. This leads us to think of 'Socrates' or 'Mr Smith' as denoting something that persists through a certain number of years, and as in some way more 'solid' and 'real' than the events that happen to him. If Socrates is ill, we think that Socrates, at other times, is well, and therefore the being of Socrates is independent of his illness; illness, on the other hand, requires somebody to be ill. But although Socrates need not be ill, something must be occurring to him if he is to be considered to exist. He is not,