An external necessity determines our condition, our existence in time, by means of the sensuous. The latter is quite involuntary, and directly it is produced in us we are necessarily passive. In the same manner an internal necessity awakens our personality in connection with sensations, and by its antagonism with them; for consciousness cannot depend on the will, which presupposes it. This primitive manifestation of personality is no more a merit to us than its privation is a defect in us. Reason can only be required in a being who is self-conscious, for reason is an absolute consecutiveness and universality of consciousness; before this is the case he is not a man, nor can any act of humanity be expected from him. The metaphysician can no more explain the limitation imposed by sensation on a free and autonomous mind than the natural philosopher can understand the infinite, which is revealed in consciousness in connection with these limits. Neither abstraction nor experience can bring us back to the source whence issue our ideas of necessity and of universality: this source is concealed in its origin in time from the observer, and its super-sensuous origin from the researches of the metaphysician. But, to sum up in a few words, consciousness is there, and, together with its immutable unity, the law of all that is for man is established, as well as of all that is to be by man, for his understanding and his activity. The ideas of truth and of right present themselves inevitable, incorruptible, immeasurable, even in the age of sensuousness; and without our being able to say why or how, we see eternity in time, the necessary following the contingent. It is thus that, without any share on the part of the subject, the sensation and self-consciousness arise, and the origin of both is beyond our volition, as it is out of the sphere of our knowledge. But as soon as these two faculties have passed into action, and man has verified by his experience, through the medium of sensation, a determinate existence, and through the medium of consciousness its absolute existence, the two fundamental impulses exert their influence directly their object is given. The sensuous impulse is awakened with the experience of life--with the beginning of the individual; the rational impulsion with the experience of law--with the beginning of his personality; and it is only when these two inclinations have come into existence that the human type is realized. Up to that time, everything takes place in man according to the law of necessity; but now the hand of nature lets him go, and it is for him to keep upright humanity, which nature places as a germ in his heart. And thus we see that directly the two opposite and fundamental impulses exercise their influence in him, both lose their constraint, and the autonomy of two necessities gives birth to freedom. LETTER XX.