To criticise the works of knowledge spontaneously effected; that is to say, to scrutinise their direction, reach, and conditions: that is today the unanimous answer of philosophers when questioned about the goal of their labours. In other terms, what they study is not so much such and such a particular "thing" as the relation of mind to each of the realities to be studied. Their object, if we must employ the word, is knowledge itself, it is the act of knowing regarded from the point of view of its meaning and value. Philosophy thus appears as a new "order" of knowledge, co-extensive with what is knowable, as a kind of knowledge of the second degree, in which it is less a question of learning than of understanding, in which we aim at progressing in depth rather than in extent; not effort to extend the quantity of knowledge, but reflection on the quality of this knowledge. Spontaneous thought--vulgar or scientific--is a direct, simple, and practical thought turned towards things and partial to useful results; seeking what is formulable rather than what is true, or at least so fond of formulae which can be handled, manipulated, or transmitted, that it is always tempted to see the truth in them; a thought which, moreover, sets out from more or less unguarded postulates, abandons itself to the motive impulses of habits contracted, and goes straight on indefinitely without self-examination. Philosophy, on the contrary, desires to be thought about thought, thought retracing its life and work, knowledge labouring to know itself, fact which aspires to fact about itself, mental effort to become free, to become entirely transparent and luminous in its own eyes, and, if need be, to effect self-reform by dissipating its natural illusions. What we have before our eyes then are the initial postulates themselves, the first spontaneous thoughts, the obscure origins of reason; and we are proceeding towards a point of departure rather than arrival. The new philosophy does not refuse to carry out this first critical task; but it carries it out in its own way after determining more precisely the real conditions of the problem. At the hour when methodical research begins, the philosopher's mind is not clean-swept; and it would be chimerical to wish to place oneself from the beginning, by some act of transcendence, outside common thought. This thought cannot be inspected and judged from outside. It constitutes, whether we wish it or no, the sole concrete and positive point of departure. Let us add that common-sense constitutes also our sole point of insertion into reality. It can only then be a question of purifying it, not in any way of replacing it. But we must distinguish in it what is pure fact, and what is ulterior arrangement, in order to see what are the problems which really are presented, and what are, on the contrary, the false problems, the illusory problems, those which relate only to our artifices of language.