Scepticism is the proclamation of mystery made in the name of thought;--a definition the contradictoriness of which leaps to the eye. It is mortally wounded both by the ancient dilemma against scepticism and by the _cogito_ of Descartes. Nevertheless, since a singular tenderness for the idea of mystery seems to have invaded the contemporary world, it is desirable to leave open no loophole whatever for misunderstanding. The _mystery_ is _life itself,_ which is an eternal _problem_ for thought; but this problem would not even be a problem, if thought did not eternally solve it. For this reason, both those who consider mystery to be definitely penetrated by thought and those who consider it impenetrable are equally wrong. The first we already know: they are the philosophists who reduce reality to pure terms of abstract thought, by breaking up the _a priori_ synthesis and by neglecting the historical element, which is ever new and ever assuming forms not determinable _a priori._ Thus, they claim to shut up the world for ever in one single act (maybe in some particular philosophic system). Through their excessive love of the infinite they make it finite; the sun and the earth and all the stars, the historical forms of life, and what is called human life, which has been known for some thousands of years, are transformed by them into categories of thought, solidified and made eternal. This conception, which appears (at least as a tendency) in certain parts of the Hegelian philosophy, is narrow and suffocating. The spirit is superior to all its manifestations hitherto known, and its power is infinite. It will never be able to surpass itself, that is to say, its eternal categories, just as God (according to the best theological doctrines) could destroy heaven and earth, but not the true and the good, which are his very essence; yet the spirit is able to surpass, and actually does surpass, its every contingent incarnation. The world, which is abstractly assumed to be more or less constant, is all in movement and becoming. Those who will be raised up to think it will know what worlds will issue from this world of ours. That we cannot know, for we must think this world which exists at our moment, and must act on the basis of it. [Sidenote: _Critique of the affirmations of mystery in philosophy._]