One common argument against substance (mind-body) dualism runs as follows. We know that consciousness is dependent on the brain, because when the brain is damaged it adversely affects consciousness and mental function. (You can prove this point to yourself experimentally by hitting yourself hard on the head with a brick.) Furthermore, it is argued, when brain function ceases altogether, consciousness disappears. (Don’t try to prove this latter point to yourself experimentally; just take it on trust.) Therefore, contra substance dualism, the mind — if it’s a real entity at all — must be ontologically dependent on the physical structures of the brain. We should be physicalists of some kind.
I come across this argument all the time in the writings of naturalists, but it strikes me as a blatant non sequitur. At most it shows that there’s a causal relationship between the mind and the body, which substance dualists insist upon anyway. (The so-called “interaction problem,” which is concerned with how there can be causation between physical and non-physical substances, is a different challenge to dualism, one I don’t propose to address here.) The fact that increasing damage to the brain leads to increasing mental impairment doesn’t at all imply that the mind cannot exist apart from the brain.
Here’s an analogy to elucidate why that’s so. Imagine a spaceship of the kind familiar from sci-fi movies. In this spaceship, the cockpit doubles up as an escape pod. In normal operation, the cockpit is attached to the main ship; whenever the ship moves, the cockpit moves with it, just as it should. If the ship is attacked with (say) photon torpedoes, the cockpit is buffeted about along with the rest of the spacecraft. When the ship is damaged, all of its systems can be affected; thus the operation of the cockpit can be impaired by damage to the ship in which it is housed.
If the ship becomes so badly damaged that it can’t move at all, the cockpit is stuck along with it, since it’s fixed to the ship. But if the spaceship is completely blown apart, the cockpit functions as an escape pod: it can detach from the doomed ship, and once detached, it can move freely again. (In line with a Christian eschatology, we could even extend the analogy such that if the parts of the ship are recovered and reassembled, the cockpit can be reattached — but that’s not necessary for the point I’m making here.)
Alternatively, think of Marvel’s Tony Stark in one of his Iron Man suits. When the bad guy hits Iron Man, Tony gets shaken about. If the suit is damaged, Tony’s ability to operate becomes impaired, and if the suit is damaged to the point where it no longer functions, Tony is grounded — until, that is, he disengages from the suit, at which point he’s able to move freely again. His ‘operation’ is no longer inhibited by the damaged suit.
The point is this: in both cases there are two distinct things that under normal operation are causally connected in such a way that damage to one impairs the function of the other, and yet the second thing can still exist independently of the first if the latter is irreparably damaged or destroyed.
The physicalist may be tempted to reply, “But both of your analogies involve two physical things that are physically connected!” Right, that’s why we call them analogies. The objection misses the point. The analogy is that we have two causally connected things, where neither depends on the other for its existence. On the substance dualist view, the body and the mind are causally connected; that’s a part of the dualist package that can be taken for granted in the defense I’m offering here. My point is simply this: the phenomenon of mental impairment as a consequence of brain damage doesn’t vindicate physicalism over against substance dualism.
Hi James,
I agree with the non sequitur charge: the evidence described doesn’t logically preclude dualism. And I really like the escape pod and Iron Man analogies as illustrating how one thing can exist and function without another even if the former and latter are currently causally connected.
But there seems to be an important difference between (i) how mental function depends on brain function (while mind is “engaged” with brain) and (ii.) how Stark’s function depends on suit function (while Stark is “engaged” with suit). (I have in mind here van Inwagen’s “remote control” argument against dualism.) And this difference seems to me to provide grounds for a good non-deductive argument for physicalism (though I don’t think it makes the evidence *on the whole* favor physicalism – I accept dualism.)
Some of Stark’s functions (i.) consist in operating the suit (e.g., operating his “palm blaster” (or whatever)), while others (ii.) don’t (e.g., Stark’s talking to himself, or Stark’s *trying* to operate his palm blaster). No matter how much damage the suit takes, as long as Stark isn’t damaged, he can still perform the second sort of function. E.g., he can still try operate his palm blaster, though perhaps it won’t work. Turning to the mind, we can draw a parallel distinction, between mental function that (i.) consists in “operating” the body (e.g., moving my hand), from mental function that (ii.) doesn’t (e.g., my thinking about a math problem, or my *trying* to move my hand). And here’s a difference from the Iron Man case: while mind is engaged with brain, *both* types of mental function can be compromised by brain damage. If my brain takes enough damage, I won’t just lose the ability to move my hand. I may (as you point out) lose consciousness altogether, and so lose the ability to even try to move my hand.
So when you conclude, “My point is simply this: the phenomenon of mental impairment as a consequence of brain damage doesn’t vindicate physicalism over against substance dualism.”, I think *a particular kind* of mental impairment (type (ii.) sketched above) provides *evidence* for physicalism (admittedly not a “vindication”, if that implies a proof). For it seems that this kind of impairment is very natural or expected on the supposition of physicalism, but somewhat surprising on the supposition of (classic substance) dualism.
Thanks, Daniel. That’s a fair response. I’m willing to grant that the kind of mental impairment you specify provides evidence for physicalism. It would indeed be less surprising on physicalism than on substance dualism. What I’m questioning in the OP is the more ambitious claim that I often hear from physicalists, as if this is some kind of knock-down argument or a crippling problem for dualism.
That said, perhaps the phenomena in question can be accounted for on a (substance) dualist basis. It’s reasonable to suppose that all creaturely mental activity requires a power source, in the broadest sense of the term (not the narrow physical sense of power). Perhaps in normal circumstances, the mind draws its power from the brain; as the brain is damaged, the mind loses its ordinary power source and thus all mental function is diminished, not merely mental function directed toward bodily movement. This is very speculative, of course. I’m just suggesting there could be plausible versions of substance dualism that could accommodate the phenomena you describe.
There’s also the Thomistic dualist view, where the mind doesn’t ontologically depend on the body, but the mind and body have to operate together in order for the mind to engage with the physical realm (or even to think about the physical realm).
Hi James,
Thanks. I agree that we can come up versions of substance dualism that can accommodate the phenomena (that brain damage can diminish *all* mental function). I’m honestly not sure how much evidential force (for physicalism) to ascribe to the phenomena. Some dualist proposals (as you admit) are speculative, but on the other hand perhaps that’s inevitable given the nature of the subject matter.
Many things that draw power from a separate thing have some sort of internal power-storage device (e.g., a laptop battery). But presumably the mind doesn’t draw power from the brain in this sense. Were that the case, then if the brain takes severe damage, we would expect this: the person immediately loses some mental function (e.g., they can no longer move any limbs), but can still perform some functions (e.g., contemplate their predicament) for a few seconds (say) before their “battery” runs out and all mental function ceases. So perhaps the idea is that the mind does not simply *get* power *from* the brain (as if power is being transferred from one thing to another), but that the relation between mind power and brain power is somehow more intimate than that.
If I think about substance dualism in the abstract, I would expect the soul to have an *intrinsic* “power supply” (even if it has to be “charged” from an external source). But perhaps our theology does not sit well with this. We were evidently made to be embodied, and that seems to go well with the idea that the mind is somehow powered by the body.
“Many things that draw power from a separate thing have some sort of internal power-storage device (e.g., a laptop battery).”
Sure, but there are many things that don’t (e.g., a lamp, a coffee machine, a desktop PC). Perhaps mental substances aren’t the sort of things that can store power internally. I think what one finds plausible (with regard to these speculations) will depend largely on one’s broader worldview.
Thanks, nice examples. Perhaps human mental substances aren’t the sort of things that can store power internally. God’s mind doesn’t need an external power source, and the same would seem to go for angels (at least there would seem to be no material source).
Both my wife (whose graduate and post-graduate training has specialized in brain-behavior relationships) and I found these analogies helpful. Do you have a recommended introduction to mind-body dualism from a Christian perspective?
Hi Marshall,
Two intros that complement each other well:
J.P. Moreland & Scott Rae, Body & Soul
Edward Feser, Philosophy of Mind: A Beginner’s Guide
I like your opening paragraph : ) Yeah, arguments for physicalism, this one and every other one I’ve encountered, are pretty terrible.
That said, your response above is far more ambitious than necessary, and so it might be better if you simply observed that the physicalist’s argument is invalid. I can see why you want to use those analogies, as you believe in life after death and so you have an eye towards defending that view. But some people find it really implausible, and so they might be turned off by the analogies you gave. (Although if you just want to shore up the existing beliefs of people like yourself then I guess that wouldn’t be a concern.)