The explanations given as to the various forms of knowledge are also explanations concerning the categories of the theoretic and theoretic-practical spirit: the intuition, the concept, historicity, type, number; and also quality and quantity and qualitative quantity, space, time, movement, and so on. They form part of that doctrine of the categories, in which the account of philosophy in the strict sense is completed. To ask what mathematics or history is, means to search for the corresponding categories; to ask what is the relation between history and mathematics, and in general how the various forms of knowledge are related to one another, means to develop genetically all these forms, which is precisely what we have attempted. [Sidenote: _The problem of the classification of the sciences and its practical nature._] But the difficult enquiry as to the forms of knowledge as categories has not been much in favour in recent times. Another problem has, on the other hand, acquired vogue. It has seemed more easy, but that is not so, because though artfully disguised, it is at bottom identical with the preceding problem. Instead of putting the question in the manner indicated above, which implies seeking out the constitution of the theoretic spirit, a modest request has been made for a classification of the various forms of knowledge, a _classification of the sciences._ Scant confidence in philosophic thought, and excessive confidence in naturalistic methods, have so operated that, unable to renounce the necessity of dominating the chaos of the various competing sciences and not wishing to have recourse to philosophic systematization, an attempt has been made to classify the sciences like minerals, vegetables, and animals. Even now there exist writers occupying professorships who claim to be specialists in classifying sciences. Volumes on this theme appear with an unprofitable frequency and abundance. [Sidenote: _False philosophic character that it assumes._]