In the thoughtful _New Essays concerning the Human Understanding_ Leibnitz develops his theory of knowledge in the form of a polemical commentary to Locke's chief work.[1] According to Descartes some ideas (the pure concepts) are innate, according to Locke none, according to Leibnitz all. Or: according to Descartes some ideas (sensuous perceptions) come from without, according to Locke all do so, according to Leibnitz none. Leibnitz agrees with Descartes against Locke in the position that the mind originally possesses ideas; he agrees with Locke against Descartes, that thought is later than sensation and the knowledge of universals later than that of particulars. The originality which Leibnitz attributes to intellectual ideas is different from that which Descartes had ascribed and Locke denied to them. They are original in that they do not come into the soul and are not impressed upon it from without; they are not original in that they can develop only from previously given sense-ideas; again, they are original in that they can be developed from confused ideas only because they are contained in them _implicite_ or as pre-dispositions. Thus Leibnitz is able to agree with both his predecessors up to a certain point: with the one, that the pure concepts have their origin within the mind; with the other, that they are not the earliest knowledge, but are conditioned by sensations. This synthesis, however, was possible only because Leibnitz looked on sensation differently from both the others. If sensation is to be the mother of thought, and the latter at the same time to preserve its character as original, _i.e._, as something not obtained from without, sensation must, first, include an unconscious thinking in itself, and, secondly, must itself receive a title to originality and spontaneity. As the Catholic dogma added the immaculate conception of the mother to that of the Son, so Leibnitz transfers the (virginal) origin of rational concepts, independent of external influence, to sensations. The monad has no windows. It bears germinally in itself all that it is to experience, and nothing is impressed on it from without. The intellect should not be compared to a blank tablet, but to a block of marble in whose veins the outlines of the statue are prefigured. Ideas can only arise from ideas, never from external impressions or movements of corporeal parts. Thus _all_ ideas are innate in the sense that they grow from inner germs; we possess them from the beginning, not developed (_explicite_), but potentially, that is, we have the capacity to produce them. The old Scholastic principle that "there is nothing in the understanding which was not previously in sense" is entirely correct, only one must add, except the understanding itself, that is, the faculty of developing our knowledge out of ourselves. Thought lies already dormant in perception. With the mechanical position (sensuous representation precedes and conditions