exactly the classes of the books and the shelves whereon they are to be found. 191. _Succession of ideas and operations_; here, then, originates the necessity of a sign by which to connect and recollect them: _relation of our understanding with the sensitive faculties_, is the reason why the signs must be sensible; _variety and simplicity of language_ constitutes its merit so far as the sign of ideas.[12] [12] See Bk. I., Ch. XXVI. CHAPTER XXX. INNATE IDEAS. 192. Among the adversaries of innate ideas there exist profound differences. The materialists maintain that man has received every thing through the senses, in such a way as to make our understanding nothing more than the product of an organism which has been advancing in perfection, just as a machine acquires, by use, a greater facility and delicacy of movement. They suppose nothing but the faculty of sensation to pre-exist in the mind; or, to speak more correctly, they admit no mind, but only a corporeal being, whose functions naturally produce what is called the intellectual development. The sensists who do not attribute to matter the faculty of thinking, do not admit innate ideas; they confess the existence of the mind, but concede to it non-sensitive faculties; all that it owns must have come to it through the senses, and it can be nothing else than a transformed sensation. Innate ideas counted other adversaries who were neither materialists nor sensists: such were the scholastics, who on the one hand defended the principle that there is nothing in the understanding which has not previously been in the senses; but, on the other hand, combated both materialism and sensism. The difference between the scholastics and the friends of innate ideas would not perhaps have been so great as it was supposed to be, had the question been proposed in another manner. 193. The scholastics regarded ideas as accidental forms, in such a way that an understanding with ideas may be compared to a piece of canvas covered with figures. The defenders of innate ideas said; "The figures already exist upon the canvas; to see them we have only to raise the veil which covers them." This explanation is somewhat forced, since it openly contradicts experience, which testifies: first, the necessity of the understanding being excited by sensations; secondly, the intellectual elaboration which we experience in thinking, and which teaches us that there is within us a kind of production of ideas.