Substance Dualism

If you believe that, in the ultimate analysis, you are a combination of a physical body and a non-physical soul, then you would be a substance dualist. This tradition has been around for thousands of years, and has been espoused by thinkers as prominent as Plato and Aquinas, as well as by most religious believers (for obvious reasons). In the 17th century, Rene Descartes articulated a philosophical defense of dualism that seemed to clinch the argument once and for all: matter is extended in space, is infinitely divisible and is unable to think; mind and thoughts, on the other hand, do not occupy space, cannot be divided and are all about thought and cognition. Case closed!

Well, not quite. Even if a non-physical world of minds and thought existed, Descartes failed to explain (as have all his followers) how it is possible for a non-physical mind to causally interact with the body and the rest of the physical world without violating everything we know about the laws of physics. Descartes said the pinneal gland, but that points to where the mechanism would take place without explaining what the mechanism is. Nevertheless, the view seemed so sensible that it was accepted by virtually everyone, with a few notable and famous exceptions.

Four hundred years of philosophic and scientific research, however, have been slowly chipping away at Descartes' seemingly clean idea, to the point that most scientists and philosophers have now come to reject dualism altogether. The following animation concisely articulates some of the major weaknesses associated with dualism, so it's worth considering it if you want your beliefs to be consistent and intellectually defensible.

To be fair, the concept of substance is much more complex and subtle than shown in the animation, so if you're curious about it, you can check it out here.

And I do have to say I find his analysis of diachronic personal identity rather simplistic and wanting. If personal identity over time were preserved simply by maintaining structure and function, then twins and clones could be said to be the same person, which is clearly not the case... it is this deficiency in the physicalist conception, perhaps, that drives people toward dualism (a wrong inference, for sure, but at least understandable).

Anyway, if you don't think minds can be split, check out the curious case of split-brain patients or the weirdness of brainspotting.
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