The Categories of the Understanding.
Besides these fundamental forms of sensuous intuition Space and Time, Kant by his analysis of Pure Reason discovered other conditions of our knowledge which could not have come from without. He divides them into twelve distinct classes, and in the phraseology of philosophy they are called Categories of the Understanding. Aristotle had previously arranged a table of Categories, but in his Logic Aristotle concerns himself with the laws of thought in general, the abstraction derived from the practical use made of them; whilst Kant studies the facts first themselves, or first principles, in their relation with certain fixed objects.
The different categories have certain traits in common, not a single one of our thoughts but will find a place in the one or the other. Another feature which characterises all is, that without them no experience would be possible, they rule our understanding. This is very marked in the category called Plurality. Let us try to think of anything without thinking of it at the same time as one or many, and we shall find it an impossibility. We cannot think of an apple or speak of an apple without picturing more than one; and Max Müller has demonstrated that rational speech is impossible, if we cannot when speaking decide whether the subject of a sentence consists of one or many.