But the great achievement of the eighteenth century in the intellectual development of the individual was that the human mind came to realize the part it was itself playing in the whole realm of science and conduct. Man began to look within. Whether he called his work an _Essay concerning Human Understanding_, or a _Treatise of Human Nature_, or a _Theory of Moral Sentiments_, or a _Critique of Pure Reason_, the aim was to study human experience. For of a sudden it was dawning upon man that, if he was then living upon a higher level of knowledge and conduct than the animal or the savage, this must be due to the activity of the mind. It appeared that man, not satisfied with "nature," had gone on to build a new world with institutions and morality, with art and science. This was no creation of instinct or habit; nor could it be explained in terms of sense, or feeling, or impulse alone; it was the work of that more active, universal, and creative type of intelligence which we call reason. Man, as capable of such achievements in science and conduct, must be regarded with new respect. As having political rights, freedom, and responsibility, man has the dignity of a citizen, sovereign as well as subject. As guiding and controlling his own life and that of others by the power of ideas, not of force, he has the dignity of a moral person, a moral sovereignty. He does not merely take what nature brings; he sets up ends of his own and gives them worth. In this, Kant saw the supreme dignity of the human spirit.