=B 11-12.=--The first half of this paragraph is transcribed practically word for word from the _Prolegomena_.[252] The second half is a close restatement of an omitted paragraph of the first edition. The chief addition lies in the concluding statement, that “experience is itself a synthetic connection of intuitions.” This is in keeping with statements made in the deduction of the categories in the second edition,[253] and in the paragraph inserted in the proof of the second analogy in the second edition.[254] The _x_ has strangely been omitted in the second edition in reference to empirical judgments, though retained in reference to synthetic _a priori_ judgments. =The proposition: everything which happens has its cause.=[255]--As we have already observed,[256] Hume influenced Kant at two distinct periods in his philosophical development--in 1756-1763, and again at some time (not quite definitely datable) after February 1772. The first influence concerned the character of concrete causal judgments; the second related to the causal axiom. Though there are few distinctions which are more important for understanding the _Critique_ than that of the difference between these two questions, it has nowhere been properly emphasised by Kant, and in several of the references to Hume, which occur in the _Critique_ and in the _Prolegomena_, the two problems are confounded in a most unfortunate manner. The passages in the _Introduction_[257] are clear and unambiguous; the influence exercised by Hume subsequent to February 1772 is quite adequately stated. The causal axiom claims to be _a priori_, and is, as Hume asserts, likewise synthetic. Consequently there are only two alternatives, each decisive and far-reaching. Either valid _a priori_ synthesis must, contrary to all previous philosophical belief, be possible, or “everything which we call metaphysics must turn out to be a mere delusion of reason.” The solution of this problem is “a question of life and death to metaphysics.” To this appreciation of Hume, Kant adds criticism. Hume did not sufficiently universalise his problem. Had he done so, he would have recognised that pure mathematics involves _a priori_ synthesis no less necessarily than do the metaphysical disciplines. From denying the possibility of mathematical science “his good sense would probably have saved him.” Hume’s problem, thus viewed, finds its final and complete expression in the formula: How are synthetic _a priori_ judgments possible? In A 760 = B 788 the account differs in two respects: first, it discusses the metaphysical validity of the causal axiom as well as its intrinsic possibility as a judgment; and secondly, reference is made to the conception of causality as well as to the axiom. The implied criticism of Hume is correspondingly modified. Otherwise, it entirely harmonises with the passages in the _Introduction_.