It is a common observation that to create a given fact is one thing, to know it when created quite another. The knowledge of what a fact really is often comes in the life of the individual years later, in the life of mankind centuries later, than the fact itself. The very persons who are directly responsible for a given fact as a rule do not know it, or know it in a very imperfect and fallacious manner; so much so that the illusions which are said to accompany human activity have passed into a proverb. The poet thinks he is singing of purity when he is really singing of sensuality, and of strength while he is really singing of weakness; he believes himself to be a dreadful pessimist and is really childishly optimistic: imagines himself a devil, when he is a good fellow without an ounce of vice in him. Philosophers deceive themselves no less. We need not go far to find examples. The philosopher we are studying supplies a whole series of them; few have been more in the dark as to the real tendencies of their own thought. The politician also deceives himself; very often he believes and declares himself to be fighting for liberty while he is a mere reactionary, or while believing himself to be serving the cause of reaction is really inciting to revolt and aiding the cause of freedom: and so on. Such illusions are easy to understand. Individuals and nations in the heat of creation, or scarcely yet passing out of such a state, can perhaps express their state of mind, but cannot treat it in the critical spirit of historical narration: and accordingly, when they cannot reconcile themselves to waiting in silence, they compose imaginary histories of themselves, _Wahrheiten und Dichtungen_ at once. In fact this proved difficulty of understanding one's actions while acting is one motive of the wise advice to speak of oneself as little as possible and of the suspicion with which autobiographies and memoirs are regarded. Such works are interesting and possibly even valuable; but they never present the strict historical truth of the facts they narrate.