But as soon as these two faculties have passed into action, and man has verified by 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 realised. 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. That freedom Is an active and not a passive principle results from its very conception; but that liberty itself should be an effect of nature (taking this word in its widest sense), and not the work of man, and therefore that it can be favoured or thwarted by natural means, is the necessary consequence of that which precedes. It begins only when man is complete, and when these two fundamental impulsions have been developed. It will then be wanting whilst he is incomplete, and while one of these impulsions is excluded, and it will be re-established by all that gives back to man his integrity. Thus it is possible, both with regard to the entire species as to the individual, to remark the moment when man is yet incomplete, and when one of the two exclusions acts solely in him. We know that man commences by life simply, to end by form; that he is more of an individual than a person, and that he starts from the limited or finite to approach the infinite. The sensuous impulsion comes into play therefore before the rational impulsion, because sensation precedes consciousness; and in this priority of sensuous impulsion we find the key of the history of the whole of human liberty.