Final answer:
René Descartes argued that the body and mind are two separate entities of different substances through his theory of substance dualism.
Step-by-step explanation:
The philosopher who argued that the body and mind were two separate entities of different substance is René Descartes. Descartes proposed the theory of substance dualism, which states that the mind and body are distinct entities. He referred to the mind as a thinking thing and the body as an extended nonthinking thing.