Both colloquially and academically, the mind-body debate grapples over the connection between the mind and body and whether it can be explained solely by physical phenomena. Is it really the case that we need immaterial substances to establish a coherent picture?
Let’s start with defining Cartesian dualism. Descartes posited that the world (universe as we would call it now) consists of two mutually exclusive, basically binary, substances. Some see ‘substance’ as an unfit description of his immaterial ‘things’, but let’s shelf that distinction for this paper. Substance dualism, says Descartes, allows us to consolidate prima-facie physical events (like a trail of falling dominos) with prima-facie non-physical events (like imagining a sphere in your mind’s eye).
Many opponents (not all, because they come in varying degrees) consider Descartes’ claim of immaterial substances epistemologically weak and propose an alternative solution that can elucidate the mind-body problem without the need for non-empirical events. They call this the completeness of physics - implying that physical laws comprise a closed system that do not interact with anything that isn’t within it. Most people phrase this notian as follows:
“All physical effects are fully determined by law by prior physical occurrences” (Papineau, p. 8).
To give this view some more flesh, let’s first discuss how it eliminates Cartesian dualism from the picture. The idea is that if all physical effects are fully determined by prior physical occurrences, we can start at any physically discernable human action (which are all actions that human observers can perceive), and moving down the causal chain, we will have covered everything there is to be known about how that action came to be. Basically, going down the causal chain of physics, we will reach a point where we discover the illuminating physical cause, which leaves no more room for Descartes’ dualism. Or at least, leaving no more room for immaterial substances that can interact with material substances. And as the latter is exactly what Descartes claims - namely that the Pineal gland allows these binaries to interact - the completeness of physics acts as a plausible counter argument to Cartesian dualism.
The most tempting way for the Cartesian to respond, is to give examples of a situation where physical explanations do not illuminate every prior cause. Say the dualist wants his opponent to explain the experience of seeing the color red. He would begin by saying that when you see red, light particles of every other color enter your pupil, and the resulting wavelength manifests itself as red in your mind through a series of chemical reactions. But if Descartes were to keep pushing and asking what that material redness that resides in Descartes’ mind’s eye consists of, the opponent would be hard-pressed to give a plausible answer. What could you say? Event subatomic particles like Quarks and Leptons would leave us wanting, because how is it that these particles exist in other non-conscious material substances where they don’t assimilate into the cognitive experience of ‘redness’. So, by presenting a situation that lacks the necessary physical explanation, Descartes undermines the completeness of physics and makes room for his dualism to enter the picture again.
I say that the above approach in the most tempting because it flatly denies the ‘completeness’ premise by empirical example - which is the very tool that completeness needs to attain validity. And although the approach makes significant progress in denying physical completeness, there is still room for retort.
People in favor of physical completeness, at this point, will claim that although they can’t describe the physical workings that comprise consciousness and other subtle mental activities now, they will be able to do so in the future. After all, the Greeks hardly knew the physical workings of the world compared to us. So the projection of our scientific progress should, according to prior experience, keep progressing towards a complete explanation. And along with the confidence that we gain from historical progress, we can additionally give examples of physical occurrences where we really do seem to have explained everything (like two billiard balls hitting each-other).
Although it seems at this point that the dualist’s opponent has set himself up for victory, there is still a noticeable crack for Cartesians to rip wide open.
The claim of physical completeness, in essence, is derived from inductive reasoning that can be mocked as shown below:
The first step of an event can be illuminated by empirical inspection.
The second step of that event can be illuminated by empirical inspection.
The third step of that event can be ...
The fourth step ...
...
Until there is nothing left to be explained.
The gaping crack in the argument stems from the epistemological weakness of induction. Sure, a physicalist can keep breaking down an event, but how can we know that for one, there will eventually be nothing left to deconstruct? Even worse, suppose that we do manage to deconstruct an action completely. What if we’re then left just as clueless as before? If anything, that would suggest the existence of immaterial things.
Worst of all, what if we do find an event, or even several events, that we can completely explain in terms of physics to an absolute degree of satisfaction. Who is then to say that this must be true for all other scenarios? And even if it turns out to be true for each situation that we inspect, how can we possibly inspect every single event? The task would be infinite, and after each step we can still ask: “Well, what about other scenarios?”.
So, although Cartesian dualism is riddled with weaknesses, the argument for the completeness of physics is not enough to cause its complete dismissal. I concede that the completeness of physics shows promise as it stems from an intuitive assumption. However, its reliance on inductive reasoning makes it vulnerable to Cartesian dualists. And this vulnerability is just what the dualist needs to stand firm within the recess of skepticism.
Gillett, Carl, and Barry Loewer. Physicalism and Its Discontents. Cambridge: Cambridge UP, 2001. Print: Papineau, Part 1: Rise of Physicalism