and perfect being Substance must have an infinite number of Attributes; but we know only two, because experience reveals no more to us. An attribute is what thought conceives of Substance as constituting its essence (essentiam substantiæ constituens). This definition implies that the whole nature of Substance must be present in every Attribute, in every fundamental form; each individual attribute must therefore, like Substance itself, be understood through itself, and its concept cannot be derived from any other concept. Everything which pertains to a given Attribute must be explained by means of this attribute alone, without reference to any other Attributes; thoughts must therefore be explained only by means of thoughts, material phenomena only by means of material phenomena. Not only Substance as such, but each of its phenomena, each Modus, e.g. man, can be regarded and explained completely under each Attribute. The nature of reality is revealed in the realm of matter as well as in the realm of mind, and the one form of manifestation cannot be derived from the other. Mind and matter (soul and body) are one and the same, only viewed from different sides.—Spinoza holds, in opposition to Descartes, that two irreducible attributes do not necessarily require two different natures, but that they can very easily pertain to one and the same nature. He differs from Hobbes in that he does not regard mind as a mere effect or form of matter, but sees in it an aspect of being quite as distinctive and primary as matter.—Descartes, Hobbes and Spinoza represent the three leading hypotheses concerning the relation of mind and matter.
Spinoza elaborates his theory of mind and matter (which in recent times has frequently been described by the unfortunate term parallelism, or the identity hy-
