Are there any presuppositions in this question, as formulated by Kant? Yes, there are. For the possibility of a system of absolutely certain knowledge is made dependent on its being built up exclusively out of judgments which are synthetic and acquired independently of all experience. "Synthetic" is Kant's term for judgments in which the concept of the predicate adds to the concept of the subject something which lies wholly outside the subject, "although it stands in some connection with the subject," [19] whereas in "analytic" judgments the predicate affirms only what is already (implicitly) contained in the subject. This is not the place for considering the acute objections which Johannes Rehmke [20] brings forward against this classification of judgments. For our present purpose, it is enough to understand that we can attain to genuine knowledge only through judgments which add to one concept another the content of which was not, for us at least, contained in that of the former. If we choose to call this class of judgments, with Kant, "synthetic," we may agree that knowledge in judgment form is obtainable only where the connection of predicate and subject is of this synthetic sort. But, the case is very different with the second half of Kant's question, which demands that these judgments are to be formed a priori, i.e., independently of all experience. For one thing, it is altogether possible [21] that such judgments do not occur at all. At the start of the Theory of Knowledge we must hold entirely open the question, whether we arrive at any judgments otherwise than by experience, or only by experience. Indeed, to unprejudiced reflection the alleged independence of experience seems from the first to be impossible. For, let the object of our knowledge be what it may--it must, surely, always present itself to us at some time in an immediate and unique way; in short, it must become for us an experience. Mathematical judgments, too, are known by us in no other way than by our experiencing them in particular concrete cases. Even if, with Otto Liebmann, [22] for example, we treat them as founded upon a certain organisation of our consciousness, this empirical character is none the less manifest. We shall then say that this or that proposition is necessarily valid, because the denial of its truth would imply the denial of our consciousness, but the content of a proposition can enter our knowledge only by its becoming an experience for us in exactly the same way in which a process in the outer world of nature does so. Let the content of such a proposition include factors which guarantee its absolute validity, or let its validity be based on other grounds--in either case, I can possess myself of it only in one way and in no other: it must be presented to me in experience. This is the first objection to Kant's view.