Let us, then, consider first the distinction between the two types of deduction in the form in which it is drawn by Kant. In the _Preface_ to the first edition,[865] Kant states that his transcendental deduction of the categories has two sides, and assigns to them the titles subjective and objective. “This enquiry, which is somewhat deeply grounded, has two sides. The one refers to the objects of pure understanding, and is intended to expound and render intelligible the objective validity of its _a priori_ concepts. It is therefore essential to my purposes. The other seeks to investigate the pure understanding itself, its possibility and the cognitive faculties upon which it rests. Although this latter exposition is of great importance for my chief purpose, it does not form an essential part of it. For the chief question is always simply this,--what and how much can the understanding and Reason know apart from all experience? not--how is the faculty of thought itself possible? The latter is as it were a search for the cause of a given effect; and therefore is of the nature of an hypothesis (though, as I shall show elsewhere, this is not really so); and I would appear to be taking the liberty simply of expressing an opinion, in which case the reader would be free to express a different opinion.[866] For this reason I must forestall the reader’s criticism by pointing out that the objective deduction, with which I am here chiefly concerned, retains its full force even if my subjective deduction should fail to produce that complete conviction for which I hope....” The subjective deduction seeks to determine the subjective conditions which are required to render knowledge possible, or to use less ambiguous terms the generative processes to whose agency human knowledge is due. It is consequently psychological in character. The objective deduction, on the other hand, is so named because it deals not with psychological processes but with questions of objective validity. It enquires how concepts which are _a priori_, and which as _a priori_ must be taken to originate in pure reason, can yet be valid of objects. In other words, the objective deduction is logical, or, to use a post-Kantian term, epistemological in character. It is indeed true, as Kant here insists, that the subjective deduction does not concern itself in any quite direct fashion with the Critical problem--how _a priori_ ideas can relate to objects. “Although of great importance for my chief purpose, it does not form an essential part of it.” This, no doubt, is one reason why Kant omitted it when he revised the _Critique_ for the second edition.[867] None the less it is, as he here says, important; and what exactly that importance amounts to, and whether it is really true that it has such minor importance as to be rightly describable as unessential, is what we have to decide.