Final answer:
The key claim for Descartes' mind-body dualism is that one could have existed without a body, supporting the notion that the mind is distinct and separable from the physical being. This reflects Descartes' foundational principle 'Cogito, ergo sum,' though it has been contested by contemporary science emphasizing the brain's role in mental processes.
Step-by-step explanation:
The claim required for René Descartes' argument for mind-body dualism is that 'You could have existed without your body or with a different body.' This statement aligns with Descartes' famous assertion, 'Cogito, ergo sum' (I think, therefore I am), where he posits that the existence of the mind is certain while the existence of the body is not. Descartes' argument suggests that the physical brain is separate from the non-physical realm of the mind, proposing that the mind could exist independently of the body. He conceived of the mind, or the 'thinking thing,' as capable of imagining, reasoning, and dreaming without requiring a physical form, a concept that has been challenged by modern neuroscience which ties cognitive processes closely to brain function.