Here, then, we have, without possibility of mistake, the fundamental doctrine of the spiritualistic philosophy of Descartes, Leibnitz, Maine de Biran, and Jouffroy. By laying down this principle the author believes himself enabled to reinstate that metaphysic which criticism had condemned. We, for our part, have no doubt of this; but we fail to see how the author can at the same time hold this principle and the Kantian principle of idealism. The "Kritik" of Kant bears upon the subject as well as the object; according to it both the one and the other are unknowable and incomprehensible noumena. The human mind is but a complex compound of sensations and categories, the unity of which is reached by the same process as the unity of external objects. No doubt Kant is, indeed, obliged to concede something to the _ego_, the _cogito_ as he calls it; but he does not very clearly say what it is; it is not a substance, not a category, not a result. "It is," says he, "the vehicle of all categories." What can be more vague? The metaphor shows both how little disposed Kant was to assign its due part to the _ego_--how vague and uncertain he left it, and at the same time how he was forced to take it into account. The _ego_, the active, continuous, self-conscious _ego_, is the rock ahead to Kant's philosophy. For how dispute the consciousness of substance and of cause, when one admits "a continuous activity dominating all states of consciousness and reducing them to unity?" What, then, is substance, according to our author? It is, he says, something that does not change considered as the necessary condition of that which changes. What is cause? Is it not the power of initiating any given movement? Now, this same consciousness which gives us the _ego_ as a continuous activity, does it not in so doing give it us as the condition of phenomena and as the productive cause of movement in voluntary efforts? Consequently, to grant that the _ego_ knows itself as _ego_, and as activity, is in point of fact to restore the notions of cause and substance which had been done away with. At most all that has been gained from criticism is the difficulty of comprehending substance and cause without objective, that is, material form. Its results, then, amount only to the incomprehensibility of matter. But the cause of metaphysic is not to be confounded with that of matter; metaphysic is not tied to the existence of materialism; and were it even led in self-defence to deny the very existence of matter altogether, one does not see that such a negation need cost it much. Descartes did not hesitate to place the existence of bodies in doubt, in order to save the existence of spirit. Malebranche did not believe that the existence of bodies could be proved except by revelation. Leibnitz did not think that bodies were more than phenomena, the reality of which was spiritual. There is, then, no common cause between the interests of metaphysic, or