The essay in question is that entitled "What is the Enlightenment?" His reply in substance is that it is the coming of age on the part of humanity: the transition from a state of minority or infancy wherein man does not dare to think freely to that period of majority or maturity in which mankind dares to use its own power of understanding. The growth of this power of free use of reason is the sole hope of progress in human affairs. External revolutions which are not the natural expression of an inner or intellectual revolution are of little significance. Genuine growth is found in the slow growth of science and philosophy and in the gradual diffusion throughout the mass of the discoveries and conclusions of those who are superior in intelligence. True freedom is inner freedom, freedom of thought together with the liberty consequent upon it of teaching and publication. To check this rational freedom "is a sin against the very nature of man, the primary law of which consists in just the advance in rational enlightenment." In contrast with this realm of inner freedom stands that of civil and political action, the principle of which is obedience or subordination to constituted authority. Kant illustrates the nature of the two by the position of a military subordinate who is given an order to execute which his reason tells him is unwise. His sole duty in the realm of practice is to obey--to do his duty. But as a member not of the State but of the kingdom of science, he has the right of free inquiry and publication. Later he might write upon the campaign in which this event took place and point out, upon intellectual grounds, the mistake involved in the order. No wonder that Kant proclaims that the age of the enlightenment is the age of Frederick the Great. Yet we should do injustice to Kant if we inferred that he expected this dualism of spheres of action, with its twofold moral law of freedom and obedience, to endure forever. By the exercise of freedom of thought, and by its publication and the education which should make its results permeate the whole state, the habits of a nation will finally become elevated to rationality, and the spread of reason will make it possible for the government to treat men, not as cogs in a machine, but in accord with the dignity of rational creatures.