Dualists, like Descartes, who maintained that there was a material body and a nonmaterial mind, were obliged to explain how the two were related. Con- versely, materialists were obliged to explain the origin of those things that we experience as men- tal events (mind). Spinoza escaped the difficulties experienced by both dualists and materialists by assuming that the mind and body were two aspects of the same thing—the living human being. For Spinoza, the mind and the body were like two sides of a coin. Even though the two sides are different, they are two aspects of the same coin. Thus, the mind and body are inseparable; anything happen- ing to the body is experienced as emotions and thoughts; and emotions and thoughts influence the body. In this way, Spinoza combined phys- iology and philosophy into one unified system. Spinoza’s position on the mind–body relationship has been called psychophysical double aspectism, double-aspect monism, or simply double aspectism.
Spinoza’s position on the mind–body relation- ship followed necessarily from his concept of God. God’s own nature is characterized by both exten- sion (matter) and thought (which is nonextended), and because God is nature, all of nature is character- ized by both extension and thought. Because God is a thinking, material substance, everything in nature is a thinking, material substance. Humans, according to Spinoza, being part of nature, are thinking, mate- rial substances. Mental activity was not confined to humans nor even to the organic world. Everything, organic and inorganic, shared in the one substance that is God, and therefore everything had both men- tal and physical attributes. For Spinoza, the unity of the mind and body was but one manifestation of an all-encompassing unity of matter and thought. Spinoza’s pantheism necessitated a panpsychism; that is, because God is everywhere, so is mind.