Now, Kant does not assert that because our moral reason must assume the possibility of this hypothetical goal civilisation is therefore moving towards it. That would be a fallacy into which he was incapable of falling. Civilisation is a phenomenon, and anything we know about it can only be inferred from experience. His argument is that there are actual indications of progress in this desirable direction. He pointed to the contemporary growth of civil liberty and religious liberty, and these are conditions of moral improvement. So far his argument coincides in principle with that of French theorists of Progress. But Kant goes on to apply to these data the debatable conception of final causes, and to infer a purpose in the development of humanity. Only this inference is put forward as a hypothesis, not as a dogma. It is probable that what hindered Kant from broaching his theory of Progress with as much confidence as Condorcet was his perception that nothing could be decisively affirmed about the course of civilisation until the laws of its movement had been discovered. He saw that this was a matter for scientific investigation. He says expressly that the laws are not yet known, and suggests that some future genius may do for social phenomena what Kepler and Newton did for the heavenly bodies. As we shall see, this is precisely what some of the leading French thinkers of the next generation will attempt to do. But cautiously though he framed the hypothesis Kant evidently considered Progress probable. He recognised that the most difficult obstacle to the moral advance of man lies in war and the burdens which the possibility of war imposes. And he spent much thought on the means by which war might be abolished. He published a philosophical essay on Perpetual Peace, in which he formulated the articles of an international treaty to secure the disappearance of war. He considered that, while a universal republic would be the positive ideal, we shall probably have to be contented with what he calls a negative substitute, consisting in a federation of peoples bound by a peace-alliance guaranteeing the independence of each member. But to assure the permanence of this system it is essential that each state should have a democratic constitution. For such a constitution is based on individual liberty and civil equality. All these changes should be brought about by legal reforms; revolutions--he was writing in 1795---cannot be justified.