Thinkers may to-day be divided into two classes: those who date from before Kant, and those who have received the initiation and, so to speak, the philosophical baptism of his critique. These two classes of minds will always have much ado to understand each other. The first are dogmatists or Pyrrhonists. The second no longer comprehend either dogmatism or Pyrrhonism. For them, the point of view has been displaced. Thanks to Kant, we judge both our knowledge and our faculty of knowing; we give an account to ourselves of the conditions in which it performs its functions, of the forms which determine it, and of the limits that it cannot pass. Kant compared, without exaggeration, the revolution which he effected in philosophy to that which the discovery of Copernicus effected in the system of the world. In philosophy also the sun has ceased to move round the earth, and the ancient illusion has been vanquished and dispersed. The idea and the reality no longer coincide; they are disjoined. The intelligible no doubt is real; but it is not certain that all the real is intelligible. Reality appears to us now as surpassing not only our knowledge, but our means of knowing. The religious notion of mystery has entered into consciousness. Man has attained to intellectual humility. Like his body, his mind is a mean between the infinitely great and the infinitely little, between nothing and everything. The deductive philosophy of the unity and necessary and continuous unfolding of an eternal substance, gives place to the philosophy of observation, which will be found to be that of the antinomies whose permanent conflict produces the ascensional progress of the world and of life. To make Kantism end in scepticism shows a lack of intelligence. His system enables us, on the contrary, to form the _scientific_ theory of science. The truth is to be found neither in dogmatism nor in Pyrrhonism, both of which Pascal combated with equal vigour. In modern science there is a certitude invincible to the subtlest Pyrrhonism; but there is also in it a sense of the limits of our knowing faculty and of the relative character of our most solid constructions which forbids man ever to be puffed up to the point of believing himself to be God. To be in this mean is to be in the truth. The same critique which establishes the validity of human knowledge lays down the limits beyond which it cannot go. We have come to know ourselves better, and that is the mark of all true progress in philosophy. _Know thyself_ is always its first rule and its final fruit. The Kantian theory of knowledge, while satisfying the mind, at the same time sets forth the essential antinomies whose normal play constitutes the very life of the ego and explains its multiple manifestations.