[CHAPTER III.]
SCIENTIFIC FRUITFULNESS OF THE IDEA OF EXTENSION.
13. In order to understand the superiority of the idea of extension over mere sensations; or rather, in order to understand that there is a true idea of extension considered in itself, and that there is no such idea of the direct and immediate objects of sensation, I wish to call attention to the fact that among all the objects of the senses, extension alone gives origin to a science.
This is a very important fact;—to explain it as it deserves, I shall establish the following propositions:
FIRST PROPOSITION.
Extension is the basis of geometry.
SECOND PROPOSITION.
Not only is extension the basis of geometry, but all that we know of the nature of bodies may be reduced to the manifestations, applications, and modifications of extension, with the addition of the ideas of number and time.