How we do or can know seems to us an inexplicable mystery, as is our existence itself. That we do know is certain. Every man knows, and in knowing knows that be knows; but how he knows no man knows. To deny is as much an act of reason as is to affirm, and no one can deny without knowing that he denies. Men may doubt many things, but universal doubt is a simple impossibility, for whoever doubts knows that be doubts, and never doubts that he doubts or that doubt is doubting. In all things and in all science we arrive at last, if we think long and deep enough, at a mystery which it is in no human power to deny or to explain, and which is explicable only in God by his divine science. Hence it is that philosophy never fully suffices for itself, and always needs to be supplemented by revelation, as nature to attain its end must not only be redeemed from the fall, but supplemented by grace. Man never suffices for himself, since his very being is not in himself; and how, then, shall philosophy, which is his creation, suffice for itself? Let philosophy go as far as it can, but let the philosopher never for a moment imagine that human reason will ever be able to explain itself. The secret as of all things is in God and with him. Would man be God, the creature the Creator? If we have seized the sense of the scholastic philosophy as represented by St. Thomas, and are right in understanding by the intelligible species of the schoolmen the light by which the object is intelligible, therefore the object itself when the object is intelligible _per se_, and the intelligible light when it is not, the ideal is objective and real, and both the old quarrel and the new are voided. Abstractions are null; genera and species are real, but creatures; ideas, as the intelligible light by which we know, are not forms of the subject, but objective and real, and in fact the light of the divine being, which, intelligible by itself, is the intelligibility of all created existences. St. Anselm's argument is, then, rigidly sound and conclusive: I think most perfect being _in re_; and therefore such being is, or I could not think it, since what is not cannot be thought. If the most perfect being, a greater than which and the contrary of which cannot be thought, be only in my thought, then I am myself greater than the most perfect being, and my thought becomes the criterion of perfection, and I am greater than God, and can judge him.