The other objection lies in this, that we have no right, at the outset of our epistemological investigations, to affirm that no absolutely certain knowledge can have its source in experience. Without doubt, it is easily conceivable that experience itself might contain a criterion guaranteeing the certainty of all knowledge which has an empirical source. Thus, Kant's formulation of the problem implies two presuppositions. The first is that we need, over and above experience, another source of cognitions. The second is that all knowledge from experience has only conditional validity. Kant entirely fails to realise that these two propositions are open to doubt, that they stand in need of critical examination. He takes them over as unquestioned assumptions from the dogmatic philosophy of his predecessors and makes them the basis of his own critical inquiries. The dogmatic thinkers assume the validity of these two propositions and simply apply them in order to get from each the kind of knowledge which it guarantees. Kant assumed their validity and only asks, What are the conditions of their validity? But, what if they are not valid at all? In that case, the edifice of Kantian doctrine lacks all foundation whatever. The whole argumentation of the five sections which precede Kant's formulation of the problem, amounts to an attempt to prove that the propositions of Mathematics are synthetic. [23] But, precisely the two presuppositions which we have pointed out are retained as mere assumptions in his discussions. In the Introduction to the Second Edition of the Critique of Pure Reason we read, "experience can tell us that a thing is so and so, but not that it cannot be otherwise," and, "experience never bestows on its judgments true or strict universality, but only the assumed and relative universality of induction." [24] In Prologomena, [25] we find it said, "First, as regards the sources of metaphysics, the very concept of Metaphysics implies that they cannot be empirical. The principles of Metaphysics (where the term 'principles' includes, not merely its fundamental propositions, but also its fundamental concepts), can never be gained from experience, for the knowledge of the metaphysician has precisely to be, not physical, but 'metaphysical,' i.e., lying beyond the reach of experience." Lastly Kant says in the Critique of Pure Reason: "The first thing to notice is, that no truly mathematical judgments are empirical, but always a priori. They carry necessity on their very face, and therefore cannot be derived from experience. Should anyone demur to this, I am willing to limit my assertion to the propositions of Pure Mathematics, which, as everybody will admit, are not empirical judgments, but perfectly pure a priori knowledge." [26]