There are in men three general faculties which are always mingled together, and are rarely exercised except simultaneously, but which analysis divides in order to study them better, without misconceiving their reciprocal play, their intimate connection, their indivisible unity. The first of these faculties is activity, voluntary and free activity, in which human personality especially appears, and without which the other faculties would be as if they were not, since we should not exist for ourselves. Let us examine ourselves at the moment when a sensation is produced in us; we shall recognize that there is perception only so far as there is some degree of attention, and that perception ends at the moment when our activity ends. One does not recollect what he did in perfect sleep or in a swoon; because then he had lost voluntary activity, consequently consciousness; consequently, again, memory. Passion often, in depriving us of liberty, deprives us, at the same time, of the consciousness of our actions and of ourselves; then, to use a just and common expression, one knows not what he does. It is by liberty that man is truly man, that he possesses himself and governs himself; without it, he falls again under the yoke of nature; he is, without it, only a more admirable and more beautiful part of nature. But while I am endowed with activity and liberty, I am also passive in other respects; I am subject to the laws of the external world; I suffer and I enjoy without being myself the author of my joys and my sufferings; I feel rising within me needs, desires, passions, which I have not made, which by turns fill my life with happiness and misery. Finally, besides volition and sensibility, man has the faculty of knowing, has understanding, intelligence, reason, the name matters little, by means of which he is elevated to truths of different orders, and among others, to universal and necessary truths, which suppose in reason, attached to its exercise, principles entirely distinct from the impressions of the senses and the resolutions of the will.[23] Voluntary activity, sensibility, reason, are all equally certain. Consciousness verifies the existence of necessary principles, which direct the reason quite as well as that of sensations and volitions. I call every thing real that falls under observation. I suffer; my suffering is real, inasmuch as I am conscious of it: it is the same with liberty: it is the same with reason and the principles that govern it. We can affirm, then, that the existence of universal and necessary principles rests upon the testimony of observation, and even of the most immediate and surest observation, that of consciousness.