Final answer:
René Descartes is associated with dualism, which states that mind and body are separate entities, while monism and Spinoza's Double Aspect Theory argue against such a separation, positing that there is only one substance with two aspects or that only physical entities exist.
Step-by-step explanation:
René Descartes believed that the mind and body were two separate entities, a view known as dualism. Dualism posits that there are two kinds of substance: mind and body (or brain), which interact or are coordinated. Descartes, through his famous statement 'Cogito, ergo sum' ('I think, therefore I am'), suggests a clear distinction between mind (non-material) and body (physical). The mind, as a non-physical entity, is considered part of the spiritual or non-physical realm.
On the other hand, monism is the belief in one kind of substance, rejecting the dualist separation. Spinoza's Double Aspect Theory encapsulates a monist view, proposing that there is only one substance with two aspects: mind and body, which are not distinct entities.
In modern philosophy, some reject dualism, leaning towards physicalism, which posits that only physical entities, including the brain, are real, and they are responsible for cognitive processes previously attributed to a 'mind.'