Correspondence, by Benedict de Spinoza, , at sacred-texts.com
[Spinoza explains his view of the infinite.]
Distinguished Sir,My statement concerning the infinite, that an infinity of parts cannot be inferred from a multitude of parts, is plain when we consider that, if such a conclusion could be drawn from a multitude of parts, we should not be able to imagine a greater multitude of parts; the first-named multitude, whatever it was, would have to be the greater, which is contrary to fact. For in the whole space between two non-concentric circles we conceive a greater multitude of parts than in half that space, yet the number of parts in the half, as in the whole of the space, exceeds any assignable number. Again, from extension, as Descartes conceives it, to wit, a quiescent mass, it is not only difficult, as you say, but absolutely impossible to prove the existence of bodies. For matter at rest, as it is in itself, will continue at rest, and will only be determined to motion by some more powerful external cause; for this reason I have not hesitated on a former occasion to affirm, that the Cartesian principles of natural things are useless, not to say absurd.
The Hague, 5 May, 1676.