According to Cartesian dualism, we don't think with our brains; we think with our minds. So for the Cartesian dualist, the brain must be nothing more than a sophisticated relay station, receiving messages from the mind and sending messages to it. On this view, those suffering from severe brain damage or from diseases such as Alzheimer's have not suffered any cognitive impairment at all. Their minds are just as good as they ever were, they have simply lost the ability to communicate with their bodies. Is this plausible? Are minds unaffected by brain damage or disease? Or does the loss of brain function also result in a loss of mental function? Which explanation is the most plausible? Why?
Descartes seems to believe that for thinking to take place, one does not need a body. His famous cogito ergo sum: 'I think therefore I am' is meant to demonstrate that 'I am a thinking being.' So, even if I doubt the existence of my body (including the brain), or that I am awake, I cannot doubt that I am a thinking being because to doubt is to think. So the fact that one thinks becomes for Descartes the first principle of philosophy. A thing which thinks is a thing which doubts, affirms, understands, feels, imagines, denies, refuses, wills, etc. This thinking is therefore a substance which does not need a body or a place and therefore does not depend on any material thing. His wax example was meant to show that a thinking self can exist without the body, indeed that it is distinct from the body. If the thinking self is a substance, then the body is an extended substance. We know that the body exists because we receive sense impressions like sight, sound and touch. This also proves to us that other bodies exist.
This establishes the major thrust of Cartesian thinking which is dualism. This dualism can be understood as 'thought' and 'extension' or mind and body (or matter). This establishes two realms, ...
This post, based on cartesian cognition, addresses the issue of whether the mind is part of the body or not. What is the mind and is it different from the brain?