One might begin by defining philosophy as knowledge of the Universe. But this definition, while accurate enough, allows the very thing that is specific to escape from us, namely the peculiar dramatic quality and the tone of intellectual heroism peculiar to philosophy and only philosophy. In effect, that definition seems to balance the one we were giving for physics when we said that it is knowledge of matter. But the fact is that the philosopher does not set himself in front of his object-the Universe-as does the physicist in front of his object, which is matter. The physicist begins by defining the profile, the outline of matter, and only then does he start working in an attempt to understand its internal structure. The mathematician defines number and extension by a similar process. Thus all the individual sciences begin by marking off for themselves a bit of the Universe, by limiting their problem, which, once limited, ceases in part to be a problem. Or to put it another way, the physicist and the mathematician know in advance the extent of their object and its essential attributes; therefore they begin not with the problem, but with something which they give or take as already known.
But the Universe on whose investigation the philosopher sets out, audacious as an Argonaut-no one knows what this is. Universe is an enormous and monolithic word which, like a vague and vast gesture, conceals this concept-everything that is-rather than stating it. Everything that is-for the moment, that is the Universe. That, note it well, nothing more than that, for when we think the concept, "everything there is," we do not know what that "everything there is" may be; the only thing we think is a negative concept, namely the negation of that which would only be a part, a piece, a fragment. So the philosopher, in contl1adistinction to every other scientist, sets sail for the unknown as such. The more or less known is a part, a portion, a splinter of the Universe. The philosopher sets himself in front of his object in an attitude which is different from that of any other expert; the philosopher does not know what his object is, of it he knows only this-first, that it is no one of the other objects; second, that it is an integral object, the authentic whole, that which leaves nothing outside, and by the same token, the only one which is sufficient unto itself. No other one of the objects which are known or suspected possesses this condition. Therefore the Universe is that which basically we do not know, that of which we are absolutely ignorant insofar as its positive content is concerned.
Swinging around this subject on an earlier spiral, we could say that to the other sciences their object is given, but the object of philosophy is precisely that which cannot be given; because it is the whole, and because it is not given, it must in a very special sense be that which is sought for, perennially sought for. There is nothing strange in the fact that the very science whose object must at the start be sought for, the science that is problematical even as to its object and its subject matter, should have a life less tranquil than the others, and should not at first sight enjoy what Kant called dersichere Gang [the steady gait]! Philosophy, which is pure theoretic heroism, will never have this sure, peaceful and bourgeois stage. Like its object, philosophy will consist in being the universal and absolute science which is sought for. This Aristotle, the first master of our discipline, calls it philosophy, the science which is sought for.
Where, one asks, does this appetite for the Universe, for the wholeness of the world, which is the root of philosophy, come from? To put it simply, that appetite, seeming peculiar to philosophy, is in fact the native and spontaneous attitude of the live mind. In the very act of living we sense, clearly or cloudily, a world about us which we assume to be complete. It is the man of science, the mathematician, the scientist, who cuts down through that integral aspect of our living world, who isolates a piece of it and out of this makes his own particular question. If knowledge of the Universe, if philosophy, does not yield truths of the same type as "scientific truth," so much the worse for scientific troth.
"Scientific truth is characterized by its exactness and the rigorous quality of its assumptions. But experimental science wins these admirable qualities at the cost of maintaining itself on a plane of secondary problems and leaving the decisive and ultimate questions intact. Out of this renunciation it makes its essential virtue, and for this, if for nothing else, it deserves applause. But experimental science is only a meager portion of the mind and the organism. Where it stops, man does not stop. If the physicist stays the hand with which he delineates things at the point where his methods end, the human being who stands behind every physicist prolongs the line and carries it on to the end, just as our eye, seeing a portion of a broken arch, automatically completes the missing airy curve.
How can we live deaf to the last, dramatic questions? Where does the world come from, whither is it going? What is the definitive power in the cosmos? What is the essential meaning of life? Confined to a zone of intermediate and secondary themes, we cannot breathe. We need a complete perspective, with foreground and background, not a maimed and partial landscape, not a horizon from which the lure of the great distances has been cut away. Lacking a set of cardinal points, our footsteps would lack direction. To assert that no manner of resolving the ultimate questions has yet been discovered is no valid excuse for a lack of sensitiveness toward them. All the more reason for feeling in the depths of our being their pressure and their hurt! Whose hunger has ever been stilled by knowing that he will not be able to eat? Insoluble though they be, those questions will continue to rise, pathetic, on the clouded vault of the night, blinking at us like the twinkle of a star. As Heine put it, the stars are the night's thoughts, restless and golden. North and South help to orient us despite theiir not being accessible cite reached simply by buying a railroad ticket.
"What I mean by this is that we are given no escape from the ultimate questions. Whether we like it or not, they live, in one fashion or another, within us. 'Scientific truth' is exact, but it is incomplete and penultimate; it is of necessity embedded in another kind of truth, complete and ultimate, although inexact, which could be called 'myth.' Scientific truth floats, then, in mythology, and science itself, as a whole, is a myth, the admirable European myth."
We insist that the physicist, and by the same token the mathematician, the historian, the artist, the politician-:-on seeing the limits of his craft, shall put back within himself. Then he finds that he himself is not solely a physicist, but that physics is only one among an innumerable series of things which he does in his man's life. At the bottom of his being, in his deepest stratum, the physicist turns out to be a man, he is a human life. And this human life is inevitably and constantly submitting itself to an integrated world, to the Universe. Before being a physicist, he is a man, and being a man, he is preoccupied with the Universe, that is to say, he philosophizes, well or poorly, spontaneously or with a care for technique, in a fashion which may be barbarous or may be cultivated. Ours will not be the road that leads over and beyond physics; on the contrary, it will draw back from physics to basic life and find the root of philosophy here. The result will not be metaphysical but ante-physical. It is born out of life itself, and as we will see clearly, life cannot avoid philosophizing, no matter in how elemental a form. Therefore the first reply to our question, "what is philosophy?" may be phrased thus -"Philosophy is-a thing which is inevitable."
Philosophy is knowledge of the Universe, or of whatever there is. We have already seen that for the philosopher this implied the need to set for himself an absolute problem, that is to say, he cannot take as his point of departure the earlier beliefs, and cannot accept anything as known in advance. The known is what is no longer a problem. Well then, that which is known outside of, apart from or previous to philosophy, is known from a point of view which is partial and not universal, is knowing on an inferior level which is no help on the heights where philosophic knowledge moves a nativitate [from birth]. Seen from philosophic heights, all other knowing has about it a touch of the ingenuous and the relatively false, that is to say, it again becomes problematical. Hence Nicolas of Cusa called the sciences docta ignorantia [learned ignorance].
This position of the philosopher, which accompanies his extreme intellectual heroism and would be so uncomfortable if it did not bear with it his inevitable vocation, imposes on his thought what I call the imperative of autonomy. This means renouncing the right to lean on anything prior to the philosophy which he may be creating, and pledging himself not to start from supposed truths. Philosophy is a science without suppositions. I understand by this a system of truths which has been constructed without admitting as groundwork any truth that is given as proven outside of that system. So there is no philosophic admission which the philosopher does not have to forge with his own means. Philosophy is an intellectual law unto itself, it is self-contained. This I call the principle of autonomy-and this links us directly to the whole critical past of philosophy; it brings us back to the great mover and shaker of modern thought and qualifies us as the latest grandsons of Descartes. But have no faith in the tenderness of grandsons. Tomorrow we are going to cast up accounts with our grandfathers. The philosopher begins by purging his spirit of received beliefs, by converting that spirit into a desert isle devoid of truths, and then, a recluse on this island, he condemns himself to a methodic procedure in the Robinson Crusoe tradition. Such was the meaning of the methodical doubt which places Descartes forever on the doorstep of philosophic knowledge. Its meaning was not simply the doubting of all that stirs doubt within us-every intelligent man does this continually-but it consists in doubting even that which in fact is not doubted, but in principle could be doubtful. This instrumental and technical doubt, which is philosophy's scalpel, has a radius of action far broader than man's habitual suspicion, in that leaving behind it that which is doubtful, it moves toward that which can be doubted.

Except from What Is Philosophy? (1928).