Kant, it is well known, did not put himself to much trouble in discovering the categories. 'I,' the unity of self-consciousness, being quite abstract and completely indeterminate, the question arises, how are we to get at the specialised forms of the 'I,' the categories? Fortunately, the common logic offers to our hand an empirical classification of the kinds of _judgment._ Now, to judge is the same as to _think_ of a determinate object. Hence the various modes of judgment, as enumerated to our hand, provide us with the several categories of thought. To the philosophy of Fichte belongs the great merit of having called attention to the need of exhibiting the _necessity_ of these categories and giving a genuine _deduction_ of them. Fichte ought to have produced at least one effect on the method of logic. One might have expected that the general laws of thought, the usual stock-in-trade of logicians, or the classification of notions, judgments, and syllogisms, would be no longer taken merely from observation and so only empirically treated, but be deduced from thought itself. If thought is to be capable of proving anything at all, if logic must insist upon the necessity of proofs, and if it proposes to teach the theory of demonstration, its first care should be to give a reason for its own subject-matter, and to see that it is necessary. (i) Kant therefore holds that the categories have their source in the 'Ego,' and that the 'Ego' consequently supplies the characteristics of universality and necessity. If we observe what we have before us primarily, we may describe it as a congeries or diversity: and in the categories we find the simple points or units, to which this congeries is made to converge. The world of sense is a scene of mutual exclusion: its being is outside itself. That is the fundamental feature of the sensible. 'Now' has no meaning except in reference to a before and a hereafter. Red, in the same way, only subsists by being opposed to yellow and blue. Now this other thing is outside the sensible; which latter is, only in so far as it is not the other, and only in so far as that other is. But thought, or the 'Ego,' occupies a position the very reverse of the sensible, with its mutual exclusions, and its being outside itself. The 'I' is the primary identity--at one with itself and all at home in itself. The word 'I' expresses the mere act of bringing-to-bear-upon-self: and whatever is placed in this unit or focus, is affected _by_ it and transformed into it. The 'I' is as it were the crucible and the fire which consumes the loose plurality of sense and reduces it to unity. This is the process which Kant calls pure apperception in distinction from the common apperception, to which the plurality it receives is a plurality still; whereas pure apperception is rather an act by which the 'I' makes the materials 'mine.'