This cause, by reason of which anything exists, must either be contained in the nature and definition of the existing thing (viz., that it pertains to its nature to exist,) or else must be beyond it--must be something different from it. "As therefore it pertains to the nature of substance to exist, so must its definition include a necessary existence, and consequently from its sole definition we must conclude its existence. But as from its definition, as already shown in notes two and three, it is not possible to conclude the existence of many substances--_ergo_, it necessarily follows that only one substance of the same nature can exist." It will be necessary for the reader to remember that Spinoza commenced his philosophical studies at the same point with Descartes. Both recognized existence as the primal fact, self-evident and indisputable. But while Descartes had, in some manner, fashioned a quality--God and God-created substance--Spinoza only found one, substance, the definition of which included existence. By his fourth proposition ("of things which have nothing in common, one cannot be the cause of the other, ") he destroyed the creation theory, because by that theory God is assumed to be a spirit having nothing in common with matter, yet acting on matter; and Lewes speaks of the fourth proposition in the following terms:--"This fallacy has been one of the most influential corrupters of philosophical speculation. For many years it was undisputed, and most metaphysicians still adhere to it. The assertion is that only like can act upon like; but although it is true that _like_ produces (causes) _like_, it is also true that like produces _unlike_; thus fire produces pain when applied to our bodies; _explosion_ when applied to gunpowder; _charcoal_ when applied to wood; all these effects are unlike the cause." We cannot help thinking that in this instance, the usually thoughtful Lewes has either confused substance with its modes, or, for the sake of producing a temporary effect, has descended to mere sophism. Spinoza's proposition is, that _substances_ having nothing in common, cannot act on one another. Lewes deals with several modes of the same substance as though they were different substances. Way, more, to make his argument the more plausible, he entirely ignores in it that _noumenon_ of which he speaks as underlying all phenomena, and uses each phenomenon as a separate existence. In each of the instances mentioned, however varied may be the modification, the essence is the same. They are merely examples of one portion of the whole acting upon another portion, and there is that in each mode which is common to the whole, and by means of which the action takes place.