This, as Vaihinger remarks, is a point of sufficient importance to justify separate treatment. But it is introduced quite incidentally by Kant, and obscures quite as much as it clarifies the main argument. It is convenient to start with the second synthesis. Kant’s argument is much clearer in regard to it than in regard to the other two. He distinguishes between empirical and transcendental reproduction. Reproduction in ordinary experience, in accordance with the laws of association, is merely empirical. The _de facto_ conformity of appearances to rules is what renders such empirical reproduction possible; “...otherwise our faculty of empirical imagination would never find any opportunity of action suited to its capacities, and would remain hidden within the mind as a dead, and to us unknown power.”[836] Kant proceeds to argue, consistently with his doctrine of objective affinity, that empirical reproduction is itself transcendentally conditioned. The form, however, in which this argument is developed is peculiar to the section before us, and is entirely new. “If we can show that even our purest _a priori_ intuitions yield no knowledge, save in so far as they contain such connection of the manifold as will make possible a thoroughgoing synthesis of reproduction, this synthesis of the imagination must be grounded, prior to all experience, on _a priori_ principles; and since experience necessarily presupposes that appearances can be reproduced, we shall have to assume a pure transcendental synthesis of the imagination as conditioning even the possibility of all experience.”[837] In the concluding paragraph Kant makes clear that he regards this _transcendental_ activity as being exercised in a twofold manner: in relation to the _empirically_ given manifold as well as in relation to the _a priori_ given manifold. How this transcendental activity is to be distinguished from the empirical is not further explained. I discuss this point below.[838] The argument of the section on the synthesis of _apprehension_, to which we may now turn back, suffers from serious ambiguity. It is not clear whether a distinction, analogous to that between empirical and transcendental reproduction, is being made in reference to apprehension. The actual wording of its two last paragraphs would lead to that conclusion. That, however, is a view which would seem to be excluded by the wider context. Kant is dealing with the synthesis of apprehension in _inner_ intuition, _i.e._ in time. By the fundamental principles of his teaching such intuition must always be transcendental. Empirical apprehension can only concern the data of the special senses. The process of apprehension referred to in the middle paragraph must therefore itself be transcendental.