pothesis) according to the deductive method, because he derives it from his definitions of Substance, Attribute and Modi. We have however already called attention to the fact that he discovered his definitions by means of the analysis of experience and of knowledge. The definition of Attribute presupposes the fundamental principle of the identity of cause and effect, previously mentioned; from this presupposition the relation between the Attributes follows in the same manner as the relation between Substance and Modi. That everything which pertains to a given Attribute must be explained by reference to that attribute is really nothing more than a metaphysical paraphrase of the principle that material phenomena can only be explained by means of material phenomena. Kepler’s vera causa makes the same demand. That this is really what Spinoza meant becomes quite apparent from the following expression: “If any one should say that this or that bodily activity proceeds from the soul, he knows not what he is talking about, and really grants that we do not know the cause of such activity.”—He nevertheless likewise calls attention to the fact that the development of the soul advances proportionately with the development of the body, and that we have no right to set arbitrary limits to the material uniformity of nature.
Spinoza does not regard the hypothesis of identity as a mere psychophysical theory. He likewise gives it an epistemological significance in that he speaks of an identity of thought with its object. Here he confuses the relation of subject and object with the relation of soul and body. This is the more remarkable, since he holds that the validity of knowledge depends on its logical consistency rather than on the agreement with its
