But Kant's refutation of subjective idealism and his vindication of the place of the object can be fully understood only when we take into account the other defect in the teaching of his predecessors that he sought in his _Critique_ to correct. In continental philosophy the reaction against mechanical and pantheistic explanations of the universe found even more definite utterance than in English psychological empiricism in the metaphysical system of Leibnitz, whose theory of self-determined monads can be understood only when taken in the light of the assertion of the rights of the subject against the substance of Spinoza and the atoms of the materialist. But Leibnitz also anticipated Kant in seeking to correct the empirical point of view of the English philosophers. True, sense-given material is necessary in order that we may have thought. "But by what means," he asks, "can experience and the senses give ideas? Has the soul windows? Is it like a writing tablet? Is it like wax? It is plain that all those who think thus of the soul make it at bottom corporeal. True, nothing is in the intellect which has not been in the senses, but we must add except the intellect itself. The soul contains the notions of being, substance, unity, identity, cause, perception, reasoning and many others which the senses cannot give" (_Nouveaux essais_, ii. 1). But Leibnitz's conception of the priority of spirit had too little foundation, and the different elements he sought to combine were too loosely related to one another to stand the strain of the two forces of empiricism and materialism that were opposed to his idealism. More particularly by the confusion in which he left the relation between the two logical principles of identity and of sufficient reason underlying respectively analytic and synthetic, deductive and inductive thought, he may be said to have undermined in another way the idealism he strove to establish. It was in seeking to close up the fissure in his system represented by this dualism that his successors succeeded only in adding weakness to weakness by reducing the principle of sufficient reason to that of formal identity (see WOLFF) and representing all thought as in essence analytic. From this it immediately followed that, so far as the connexion of our experiences of the external world does not show itself irreducible to that of formal identity, it must remain unintelligible. As empiricism had foundered on the difficulty of showing how our thoughts could be an object of sense experience, so Leibnitzian formalism foundered on that of understanding how the material of sense could be an object of thought. On one view as on the other scientific demonstration was impossible. Kant.