[7] No doubt Kant would allow that at least some categories, e. g. the conception of cause and effect, are principles of synthesis of a manifold which at any rate contains an empirical element, but it _includes_ just one of the difficulties of the passage that it implies that _a priori_ knowledge either is, or involves, a synthesis of pure or _a priori_ elements. [8] B. 92-4, M. 56-8. [9] Kant, of course, thinks of this activity of thought, as identical with that which brings particulars under a conception. In the second place, the passage incidentally explains why, according to Kant, the forms of judgement distinguished by Formal Logic do not involve the categories.[10] For its doctrine is that while thought, if exercised under the conditions under which it is studied by Formal Logic, can only analyse the manifold given to it, and so has, as it were, to borrow from the manifold the unity through which it relates the manifold,[11] yet if an _a priori_ manifold be given to it, it can by means of a conception introduce into the manifold a unity of its own which could not be discovered by analysis of the manifold. Thus thought as studied by Formal Logic merely analyses and consequently does not and cannot make use of conceptions of its own; it can use conceptions of its own only when an _a priori_ manifold is given to it to deal with. [10] Cf. pp. 155-6. [11] In bringing perceptions under a conception, thought, according to Kant, finds the conception _in_ the perceptions by analysis of them, and in relating two conceptions in judgement, it determines the particular form of judgement by analysis of the conceptions.