Paul Draper mentioned this argument in his debate with William Lane Craig in 1998. Draper is very very fond of the WAP (weighted average principle) and he is using it here as well. The idea, according to Draper, is that since theism already starts out with at least one non-physical mind that is distinct from the universe, and since God is omnipotent, God could either create minds that are independent of the brain, or minds that are dependent or identical to the brain. Even if we might expect the former over the latter on theism, Draper's real point is that on naturalism, minds have to be dependent or identical to the brain. There is no other option on naturalism. Thus, the fact that we have discovered that minds are dependent or identical to the brain, by the WAP, confirms naturalism over theism.
RESPONSE: Now, one of the best ways to defeat these types of arguments that invoke the WAP is too show that it isn't the case after all, that on theism, option x and y were feasible, but in fact, only x was feasible. In other words, what the theist can do is show that God didn't have the option of creating minds that were either independent or dependent, but only had to option of creating minds that were dependent on the brain. If that can be done, then on the WAP, our discovery that human minds are dependent on the brain would not lend more support to theism or naturalism either way. So then, how can this be done? I propose that we consider the implications of a common criticism that is often ledged against substance dualism, which is a view about human nature that claims that human beings are composed of two distinct substances, body and soul, and on this view the mind is independent of the brain. So then, Draper thinks substance dualism should be true if God existed, but since it isn't, that fact confirms naturalism over theism. Okay, now we are ready to look at a criticism of substance dualism to see how it defeats Draper's argument:
"By assuming a deterministic physical universe, the objection can be formulated more precisely. When a person decides to walk across a room, it is generally understood that the decision to do so, a mental event, immediately causes a group of neurons in that person's brain to fire, a physical event, which ultimately results in his walking across the room. The problem is that if there is something totally nonphysical causing a bunch of neurons to fire, then there is no physical event which causes the firing. This means that some physical energy is required to be generated against the physical laws of the deterministic universe - this is by definition a miracle and there can be no scientific explanation of (repeatable experiment performed regarding) where the physical energy for the firing came from.[30] Such interactions would violate the fundamental laws of physics. In particular, if some external source of energy is responsible for the interactions, then this would violate the law of the conservation of energy.[31] Dualistic interactionism has therefore been argued against in that it violates a general heuristic principle of science: the causal closure of the physical world (Wikipedia)."
Personally, I find this criticism devastating to substance dualism precisely because substance dualism implies that human beings are capable of performing MIRACLES! Since Draper thinks that substance dualism is to be expected on theism, that means that he thinks that human beings should be able to perform miracles! However, on theism and naturalism, only God, or a being maximally powerful can perform miracles. But, it is logically impossible for God to create another, not to mention many other, maximally powerful beings because any other being that exists must be within the power of God to create or not. But then the existence of that being depends asymmetrically upon God. So God has power over it, while it lacks this power over God. So there can be at most one omnipotent God. Moreover, as Michael Tooley states in his debate with Craig, "...given what we know about the universe, it would be impossible for there to be a being that was omnipotent and omniscient and that was physical in nature." Even if it wasn't logically impossible for God to create another omnipotent being that could perform miracles, we know that human beings wouldn't fit that bill. So, unless Draper could show that god was obligated to create another being that was maximally powerful (which is impossible anyway), his argument is not a good one because God didn't have the option of creating little human miracle workers which have minds independently of their brains. Indeed, if Draper got his wish of substance dualism, that would mean that the number of miracles that human beings will have performed by now is much much much much greater than the number of miracles God has ever performed! Strange indeed.
"By assuming a deterministic physical universe, the objection can be formulated more precisely. When a person decides to walk across a room, it is generally understood that the decision to do so, a mental event, immediately causes a group of neurons in that person's brain to fire, a physical event, which ultimately results in his walking across the room. The problem is that if there is something totally nonphysical causing a bunch of neurons to fire, then there is no physical event which causes the firing. This means that some physical energy is required to be generated against the physical laws of the deterministic universe - this is by definition a miracle and there can be no scientific explanation of (repeatable experiment performed regarding) where the physical energy for the firing came from.[30] Such interactions would violate the fundamental laws of physics. In particular, if some external source of energy is responsible for the interactions, then this would violate the law of the conservation of energy.[31] Dualistic interactionism has therefore been argued against in that it violates a general heuristic principle of science: the causal closure of the physical world (Wikipedia)."
Personally, I find this criticism devastating to substance dualism precisely because substance dualism implies that human beings are capable of performing MIRACLES! Since Draper thinks that substance dualism is to be expected on theism, that means that he thinks that human beings should be able to perform miracles! However, on theism and naturalism, only God, or a being maximally powerful can perform miracles. But, it is logically impossible for God to create another, not to mention many other, maximally powerful beings because any other being that exists must be within the power of God to create or not. But then the existence of that being depends asymmetrically upon God. So God has power over it, while it lacks this power over God. So there can be at most one omnipotent God. Moreover, as Michael Tooley states in his debate with Craig, "...given what we know about the universe, it would be impossible for there to be a being that was omnipotent and omniscient and that was physical in nature." Even if it wasn't logically impossible for God to create another omnipotent being that could perform miracles, we know that human beings wouldn't fit that bill. So, unless Draper could show that god was obligated to create another being that was maximally powerful (which is impossible anyway), his argument is not a good one because God didn't have the option of creating little human miracle workers which have minds independently of their brains. Indeed, if Draper got his wish of substance dualism, that would mean that the number of miracles that human beings will have performed by now is much much much much greater than the number of miracles God has ever performed! Strange indeed.