Interactive Dualism

The primary problem of Dualism—many would say the defeater of Dualism—is how nonphysical substances could possibly interact with physical substances, especially given the common assumption that the physical world is a closed system. Also called the "pairing problem," how could an immaterial thing, the mind, interact with a material thing, the body (or brain)? Notwithstanding our folk perception that the physical world affects my mind through my senses and my mind affects the physical world through my actions, most scientists and philosophers deny this is what is in fact happening. There would be no commonalities between physical and nonphysical substances, no means of exchange—the problem of mental causation on steroids. Moreover, if nonphysical substances could somehow affect and alter physical substances, wouldn't that require a transference of energy, and wouldn't such an addition violate the sacrosanct physical law of the conservation of energy? (Section: Robinson, 2023; Interactionism, 2023).

The Interaction Problem

Advocates of Interactive Dualism (not that there are many among scientists and philosophers) say they have resources. They reject the weak dualism of Epiphenomenalism where the physical affects the mental but the mental does not affect the physical (9.1.2). They can claim that the interaction problem is founded on archaic 19th century, billiard-ball physics, where causation requires hard substances to be in physical contact, to touch one another, as it were.

Quantum mechanics, on the other hand, allows for various, albeit speculative ways, for the mental to affect the physical, even beyond the classic but controversial view that an “observer” is needed to “collapse” the wave function. Moreover, because quantum mechanics introduces fundamental uncertainty into the universe, and if by this indeterminism holds, nonphysical substances might enjoy “wiggle room” to effect causation.

Speculative Solutions

Advocates can also appeal to different kinds of ethereal forces or energy transference systems. Perhaps mental powers can influence the distribution but not the quantity of energy in the brain (“a little more here, a little less there” does seem a bit of a cheat). Perhaps each individual brain is not a causally closed system so that the conservation of energy need not apply.

Perhaps causal closure for the entire universe is also a 19th century invention, based on classical thermodynamics and statistical mechanics, which are now superseded by quantum mechanics, general relativity, dark matter, dark energy, and who knows what else? (I can make up another. Since string theory offers, depending on flavor, 10, 11 or 26 “compactified” extra dimensions, why couldn't nonphysical substances work via these extra dimensions? I can conceive of a precedent for this. To account for the “hierarchy problem” in physics, where gravity is vastly weaker than the other fundamental forces, some postulate that gravity “leaks” or “bleeds” into these extra dimensions.) It gets crazy.

That's not all. Perhaps, one could just blow away the interaction problem by just asserting that in systems that have minds, the law of conservation of energy is false. Perhaps because downward causation goes to the lower physical levels and emergence is enabled, the causal completeness of physics is wrong (Ellis, 2019). Further, because the whole idea of a closed physical system is based on the assumption that there are no nonphysical forces involved, wouldn't this assumption undermine the argument against interaction by making it circular? Then there is “overdetermination,” where mental and physical factors can each, independently, affect actions—an approach that, while possibly solving one problem, creates other problems (Robinson, 2023; Interactionism, 2023).

Theological Responses

Finally, there is always a theological solution. God can help. God could have created souls with powers, especially since “real” (i.e., libertarian) free will is an essential part of “God's plan,” such that neither conservation of energy nor determinism holds, at least with respect to minds. (It is challenging how even God could make this coherent.)

Christian philosopher William Lane Craig describes himself as a “dualist-interactionalist” in that “the brain is itself part of... the physical reality with which the soul immediately interacts (Craig, 2015). He argues that even though souls do not have spatial locations, “the question becomes why we should think that only spatial relations can pair a cause with its effect. Prima facie this seems overly restrictive” (Craig, 2023).

I mustn't forget “Occasionalism,” the idea that created substances, physical and nonphysical, cannot be efficient causes of events in themselves and that all events are caused directly by God. This would mean that while mind and body appear to interact, in fact it is God that is changing each separately and ceaselessly. While Occasionalism is dismissed (often ridiculed), there is a kind of logic here. If God acts as intermediary, as it were, between nonphysical and physical substances, then because God would have created both in the first place, this would make the apparent causal connection between nonphysical and physical substances not especially troublesome for God to bring about. This way of thinking—all these possible mechanisms for Interactive Dualism—reflects the depth of Dualism's problem.