In the first part of my look at dualism I explained how an apt use of Bayesian reasoning offers a knock-down argument against belief in dualism but simple careful reasoning shows us why the conversation about probabilities needn’t be had. There are fundamental problems with attributing consciousness to a non-physical substance.
There are two common objections to substance dualism in principle. The first is it’s not clear what the alternative to physical entities is supposed to be as saying “non-physical substance” is a bit like saying “non-wet liquid.” The second, and likely intractable, problem is called the mind-body problem which asks how a non-physical substance and a physical substance are supposed to interact. However these two issues are merely a side-effects of accepting a broken framework.
Substance dualism is not an explanation for consciousness at all, and couldn’t hope to be one, but instead has all of the familiar properties of nonexplanations. It posits an ineffable entity, the non-physical substance (whatever that is!), which claims to account for a complex phenomenon, consciousness, but leaves that phenomenon still completely in mystery. Indeed many dualists cherish this mystery, mistaking our current ignorance for mystery being an inherent property of consciousness. This wallowing in ignorance combined with an ineffable substance which is supposed to account for some mysterious biological trait has has a strong historical parallel, it’s called vitalism. Just as vitalism tried to account for the “property of life” by appealing to the mysterious elan vital, dualism attempts to account for consciousness by appealing to the mysterious non-physical substance.
Neither account has the possibility of progress because they declared their respective phenomena as inherently mysterious. More importantly neither vitalism nor dualism predicts anything testable at all and offers only a proper name in place of a predictive model. While this may offer the illusion of an explanation, with no predictive power behind the theories they amount to being able to explain any outcome which means they really explain nothing. Most simply if we can’t test or even observe the “non-physical substance” said to be the seat of consciousness this is no different from saying “consciousness is magic.” Of course anyone who openly argued consciousness can’t be due to physical processes because consciousness is magic would rightly be laughed at. Whether dualists realize it or not, it seems to me this is indeed what is being proposed.