a. Spinoza’s first definition is of the Cause of itself. He says: “By that which is _causa sui_, its own cause, I understand that whose essence” (or Notion) “involves existence, or which cannot be conceived except as existent.” The unity of existence and universal thought is asserted from the very first, and this unity will ever be the question at issue. “The cause of itself” is a noteworthy expression, for while we picture to ourselves that the effect stands in opposition to the cause, the cause of itself is the cause which, while it operates and separates an “other,” at the same time produces only itself, and in the production therefore does away with this distinction. The establishing of itself as an other is loss or degeneration, and at the same time the negation of this loss; this is a purely speculative Notion, indeed a fundamental Notion in all speculation. The cause in which the cause is identical with the effect, is the infinite cause (_infra_, p. 263); if Spinoza had further developed what lies in the _causa sui_, substance with him would not have been rigid and unworkable. b. The second definition is that of the finite. “That thing is said to be finite in its kind which can be limited by another of the same nature,” For it comes then to an end, it is not there; what is there is something else. This something else must, however, be of a like nature; for those things which are to limit each other must, in order to be able to limit each other, touch each other, and consequently have a relation to each other, that is to say they must be of one nature, stand on a like basis, and have a common sphere. That is the affirmative side of the limit. “Thus a thought is” only “limited by another thought, a body by another body, but thoughts are not limited by bodies nor” conversely “bodies by thoughts.” We saw this (p. 244) with Descartes: thought is an independent totality and so is extension, they have nothing to do with one another; they do not limit each other, each is included in itself. c. The third definition is that of substance. “By substance I understand that which exists in itself and is conceived by itself, _i.e._ the conception of which does not require the aid of the conception of any other thing for its formation (_a quo formari debeat_);” otherwise it would be finite, accidental. What cannot have a conception formed of it without the aid of something else, is not independent, but is dependent upon that something else.