How many times have we demonstrated the vanity of the efforts of the empirical school to disturb the existence or weaken the bearing of universal and necessary principles! Listen to this school: it will say to you that the principle of cause, given by us as universal and necessary, is, after all, only a habit of the mind, which, seeing in nature a fact succeeding another fact, puts between these that connection which we have called the relation of effect to cause. This explanation is nothing but the destruction, not only of the principle of causality, but even of the notion of cause. The senses show me two balls, one of which begins to move, the other of which moves after it. Suppose that this succession is renewed and continues; it will be constancy added to succession; it will by no means be the connection of a causative power with its effect; for example, that which consciousness attests to us is the least effort of volition. Thus a consequent empiricist, like Hume,[19] easily proves that no sensible experience legitimately gives the idea of cause. What we say of the notion of cause we might say of all notions of the same kind. Let us at least instance those of substance and unity. The senses perceive only qualities, phenomena. I touch the extension, I see the color, I am sensible of the odor; but do our senses attain the substance that is extended, colored, or odorous? On this point Hume[20] indulges in pleasantries. He asks which one of our senses takes cognizance of substance. What, then, according to him and in the system of empiricism, is the notion of substance? An illusion like the notion of cause. Neither do the senses give us unity; for unity is identity, is simplicity, and the senses show us every thing in succession and composition. The works of art possess unity only because Art, that is to say, the mind of man puts it there. If we perceive unity in the works of nature, it is not the senses that discover it to us. The arrangement of the different parts of an object may contain unity, but it is a unity of organization, an ideal and moral unity which the mind alone conceives, and which escapes the senses. If the senses are not able to explain simple notions, much less still are they able to explain the principles in which these notions are met, which are universal and necessary. In fact, the senses clearly perceive such and such facts, but it is impossible for them to embrace what is universal; experience attests what is, it does not reach what cannot but be. We go farther. Not only is empiricism unable to explain universal and necessary principles; but we maintain that, without these principles, empiricism cannot even account for the knowledge of the sensible world.