In his _Critique of Pure Reason_ Kant endeavoured, at a time when speculation of a dogmatic and uncritical kind was current, to call attention to the necessity for examining the instrument of knowledge itself, and thereby discovering its fitness or inadequacy, as the case might be, for dealing with the problems which philosophy proposes to investigate. This was a word spoken in due season and, however much subsequent philosophy has deviated from the conclusions of Kant, it has at least remembered the significance of his advice. The result has been that the attitude adopted by philosophers to the problems before them has been determined largely by the kind of answer which they offer to the problems of knowledge itself. Obviously a mind which asserts that we can never be sure of knowing anything (or as in some cases, that this assertion is itself uncertain) will see all questions through the green-glasses of scepticism. On the other hand, a thinker who believes that we do have knowledge of certain things and can be certain of thiss, whether by objective proof or a subjective intuition, is sure to have, not only a different conclusion about problems, but, what is probably more important for the philosophic spirit, a different means of approaching them. Writing in 1860 on the general state of philosophy, Renan pointed out, in his Essay _La Métaphysique el son Avenir_[3] that metaphysical speculation, strictly so-called, had been in abeyance for thirty years, and did not seem inclined to continue the traditions of Kant, Hegel, Hamilton and Cousin. The reasons which he gave for this depression of the philosophical market were, firstly, the feeling of the impossibility of ultimate knowledge, a scepticism of the instrument, so far as the human mind was concerned, and secondly, the rather disdainful attitude adopted by many minds towards philosophy owing to the growing importance of science—in short, the question, “Is there any place left for philosophy; has it any _raison d’être_?” [3] Essay published later (1876) in his _Dialogues et Fragments philosophiques_. Cf. especially pp. 265-266. The progress of the positive sciences, and the assertions of many that philosophy was futile and treacherous, led philosophy to give an account of itself by a kind of _apologia pro vita sua_. In the face of remarks akin to that of Newton’s “Physics beware of metaphysics,” the latter had to bestir itself or pass out of existence. It was, indeed, this extinction which the more ardent and devoted scientific spirits heralded, re-iterating the war-cry of Auguste Comte.