Doctrine of Man (Part 10): Arguments against Dualism-Interactionism

Arguments against Dualism-Interactionism

In our most recent lesson, we discussed philosophical arguments in support of dualism-interactionism with regard to the soul. Today I would like to discuss some philosophical and scientific objections to dualism-interactionism.

Doubtless the most important philosophical objection to dualism-interactionism is that it posits a causal connection between mind and matter that is utterly mysterious. We have no understanding how a non-physical substance could have physical causal effects. The objection thus presents a challenge to dualism-interactionism, the view that the mind and body are causally interactive.

Perhaps the most powerful response by anthropological dualists to the present objection is to point out that we have good positive reasons to think that the soul is an immaterial substance that causally affects the body, even if we do not understand how. Similarly, we must not forget that we have sound theistic arguments that support divine incorporeality. Arguments such as the kalām cosmological argument, the teleological argument from the fine-tuning of the universe, and the argument from the uncanny applicability of mathematics in physics provide powerful reasons for thinking that there is a transcendent Mind who has created the universe. These arguments provide a strong cumulative case in support of dualism-interactionism that may well outweigh expressions of incredulity based on our ignorance of how the mental affects the physical.

In fact, it seems to me that the dualist-interactionist can turn the tables and argue cogently that the materialist claim that causal interaction is impossible is incapable of rational affirmation. I have reference here to Alvin Plantinga’s celebrated Evolutionary Argument against Naturalism (EAAN). Plantinga argues that naturalism is self-defeating because if our cognitive faculties have evolved by naturalistic processes, they are aimed, not at truth, but at survival, and so cannot be relied on to produce true beliefs. Because our mental states (assuming that we have such states) have absolutely no effect on our brain states, the content of our beliefs is irrelevant to our survivability. All that matters is our physical behavior, not the truth of our beliefs. So long as we act in ways conducive to survival, it literally does not matter what we believe. But if we cannot rely on our cognitive faculties to produce true beliefs, then the belief in naturalism is itself undermined, since it has been produced by those very cognitive faculties. So naturalism is self-defeating

Now EAAN is not so much an argument against naturalism as an argument against materialism. If the naturalist were to embrace dualism-interactionism, he would be immune to the argument. For though a naturalist, he would recognize the reality and causal efficacy of souls and, hence, their possible selective advantage in the evolutionary struggle for survival.

What Plantinga’s argument is really about is the so-called causal closure of the physical (CCP). “This is the assumption that if we trace the causal ancestry of a physical event, we need never go outside the physical domain.”[1] The closure principle requires that all physical events have only physical causes. If there do exist immaterial entities, they are irrelevant because of the causal closure of the physical domain. Materialists may either embrace or deny the reality of mental states, but they all deny their causal efficacy in the material world. Plantinga’s argument is therefore best cast as the Evolutionary Argument against the Causal Closure of the Physical (EAACCP).

So Plantinga’s argument is directly relevant to the present objection based on the impossibility of causal interaction between the soul and body.  For the objection two causal interaction entails the causal closure of the physical. But if EAACCP is sound, then the materialist’s claim that the soul and body cannot interact cannot be rationally affirmed and collapses in self-defeat. William Hasker wryly comments, “To say that this constitutes a serious problem for physicalism seems an understatement.”[2]

In sum, the most widespread and influential philosophical objection to dualism-interactionism fails. Given the sound arguments for a transcendent Creator and Designer of the universe, we can be confident that God can interact causally with the physical world, even if we do not understand how, just as, given the arguments for the existence of the soul, the dualist-interactionist can be confident that the soul does interact causally with the body, even if we do not understand how. Finally, the impossibility of causal interaction between soul and body cannot be rationally affirmed, since to affirm the causal closure of the physical is self-defeating and irrational.

Next I want to consider a scientific challenge to dualism-interactionism arising from some fascinating experiments performed by a brain scientist named Benjamin Libet. He conducted a series of experiments in which people were instructed to press a button with their finger while he monitored their brain activity. What Libet discovered was that prior to a person’s awareness of his decision to press the button, a brain signal had already occurred which later resulted in his finger’s moving to press the button. So the sequence of events goes like this:

1. There is a brain signal about 550 milliseconds prior to the finger’s moving.

2. There is an awareness of the decision in consciousness about 200 milliseconds prior to the finger’s moving.

3. The finger moves and presses the button.

So the brain signal actually occurs prior to the act of consciousness in which one is aware of the decision to press the button.

There is no consensus concerning the interpretation or the significance of Libet’s experiments. But as you can imagine, some people have taken this to be proof of determinism or even materialism because before the awareness to press the button even occurs, a brain signal has already been sent to make the finger move.

But such an inference would be overdrawn. In a second run of experiments, Libet discovered that even after the awareness of the decision to press the button had occurred, people still retained the ability to veto the decision and not to press the button. So they still retained the ability to refrain from the decision that had earlier been made. Some interpreters therefore take this brain signal to press the button to indicate merely a readiness potential which the patient may either then go along with or may veto. So the bottom line is the person still has control over his decision. Libet himself considered his experimental results to be fully compatible with the existence of free will.

The more fundamental point, though, to be made about these experiments, which struck me very forcefully as I reflected on these results, is that this is exactly what the dualist-interactionist should expect to happen. For the dualist-interactionist, the soul or the mind doesn’t act independently of the brain. Rather, as Sir John Eccles, the Nobel Prize-winning neurologist whom I mentioned earlier in this course, has pointed out, on a dualist-interactionist view the soul uses the brain as an instrument for thought, just as a pianist uses a piano as an instrument to produce music. So of course the soul’s decisions are not simultaneous with the soul’s awareness of those decisions – how could they be? Given the brain’s reliance upon finite velocity neural signals in order to think, the soul could not have a simultaneous awareness of its decisions. Rather, given the soul’s reliance upon the brain and the finite velocity of neural signals, there has to be a time lag between the soul’s decision and the soul’s conscious awareness of that decision. In Libet’s experiments, since the relevant neural signals travel at finite velocities, of course it takes a little time for the soul’s decision to come to conscious awareness. This is exactly what we should expect on a dualist-interactionist view of the soul and the body.

The German philosopher Uwe Meixner, who is a dualist-interactionist, has this to say about Libet’s experiments,

For making an informed decision, the self needs to be conscious of the facts relevant to the decision prior to making the decision; but   . . . the self certainly does not need to be conscious of making the decision at the very same time it makes it. . . . the consciousness of a state of affairs P being (presently) the case is always somewhat later than the actual fact of P’s being the case. . .[3]

For example, when you are talking to another person, because of the finite velocity of light signals and the finite velocity of sound waves and the finite velocity of your nerve signals, what you are experiencing as present is always a little bit in the past. You never have an actual present awareness of what is happening around you. There is a tiny time lag due to the finite velocity of these various signals that is imperceptible to us because it is so short. So Meixner goes on to say, “it is hardly surprising that the consciousness of making a decision is no exception to this general rule, which is due to the dependence of consciousness on neurophysiology.”

I want to emphasize that on this understanding the soul’s decision is not unconscious – it is conscious – but it just takes a little while for that decision to become conscious, due to the finite velocity of neural signals. Just as we never see anything that is actually presently there because of the finite velocity of light but see events as they were just slightly in the past, in the same way we don’t have a consciousness of our own decisions simultaneously with our making them, but we have it unnoticeably afterwards.

If therefore the soul has the ability to think without being causally determined, then, as Meixner says, all it needs in order to make responsible, informed, free decisions is consciousness of the relevant facts prior to its making a decision. And it has that. But the soul doesn’t need to be aware or conscious of the decision itself simultaneously with its making that decision in order for the decision to be responsible, informed, and free.

So in response to Libet’s experiments, it seems to me that they are exactly what we ought to expect if dualism-interactionism is true. The soul uses the brain as an instrument for thinking.

We now come to our second topic of discussion which is trichotomy versus dichotomy with respect to human being.