In his writings, especially The Ethics, Benedict de Spinoza logically defined existence and provided logical proof of his definitions. He used logical progressions and relationships among those statements he considered to have been proven to make his conclusions. In the readings consulted, Spinoza did not really argue for or against the existence of God, though he stated that the existence of God was a logical conclusion. He took that as a given. What Spinoza was attempting was a definition of the nature of God and of all existence. What he finally proved to his satisfaction was that God is everything which exists, that God is infinite and eternal and that everything else proceeds from the mind of God, that is, all existence is thought in the mind of God.In the translated work “Of God” Spinosa began with simple precepts which he related, such as:
“PROP. VII. -- Existence belongs to the nature of substance.DEMONSTR. -- The production of substance is impossible (by Coroll. to preceding Prop.). Substance, therefore, is the cause of itself; that is (by Def. 1), its essence necessarily involves existence; or, in other words, existence belongs to its nature. Q. E. D.PROP. VIII. -- All substance is necessarily infinite.”(Spinoza 7)This proof is at the beginning of his writing, and it identifies “substance” (something which exists) as being infinite and states the conservation of matter theorem very simply.