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Defenders: Doctrine of Man (Part 11): A Challenge to Dualism-Interactionism – The Libet Experiments
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Welcome to Defenders, the teaching class of Dr. William Lane Craig. Today, the Doctrine of Man, Part 11. For more information and resources from Dr. Craig, go to reasonablefaith.org Good morning and.
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Welcome to Defender's class. As you can see, we are meeting under rather unusual circumstances this morning. Because of the coronavirus epidemic, we can no longer meet together as a class. And the church where we normally film the class is also closed. And so we can't even record. But we are not going to be overcome by this virus. We're going to find a way around it. So I am recording today in the safety of my home office and we'll be broadcasting this worldwide to our Defenders audience that follows us every Sunday morning. Now, in our most recent lesson, we discussed philosophical arguments in support of dualism interactionism with regard to the soul. Today I want to consider a 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 when he monitored their brain activity. And 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 fingers moving to press the button. So the sequence of events goes like this. Number one, there is a brain signal about 550 milliseconds prior to the fingers moving. Two, there is an awareness of the decision in consciousness which occurs about 200 milliseconds prior to the fingers moving. And finally, number three, the finger then moves and presses the button so that the brain signal actually occurs prior to to the act of consciousness in which one is aware of the decision to press the button. Now, 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, and people still retained the ability to veto the decision and not 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 then either go along with or may veto. So the bottom line is that the person still has control over his decision. Libett 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 force as I reflected on the 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've mentioned earlier in this course, as pointed out, on a dualist interactionist view, the soul uses the brain to think 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. And 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. And 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 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 Leavitz experiments and I quote. For making an informed decision, the self needs to be conscious of the facts relevant to the decision and prior to making the decision. But the self 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 the of P's being the case. So, for example, when you're 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. And 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, and I quote, it is hardly surprising that 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 of. 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 are just slightly in the past. In the same way, we do not 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 to do 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. And 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. Let me say just a brief word about the debate over whether human beings are dichotomous or trichotomous in their composition. That is to say, are we, as human beings, composites of body and soul. Or are we composites of some other entity as well, for example, body, soul, and spirit, as some verses in the New Testament seem to suggest? Now, this question, I think, is somewhat academic. Since the fundamental question is. Is whether, in contrast to anthropological monism, we hold that there is an immaterial constituent in man in addition to the body. But as for dichotomy, trichotomy. It seems to me that there isn't any sort of strong and consistent distinction in scripture or philosophy. That can be drawn between the soul and the spirit. If you press this kind of language. To give you a different ontological reality, a substance, the spirit, which is different from the soul. Then I think you're going to proliferate entities unnecessarily. Because the Scripture also talks about things like the heart and the mind and the inner man. If you press the language of scripture about spirit, Then what about these other entities as well? You're going to get human beings as composites of all sorts of things. Rather, I think it's best to see the difference between soul and spirit. As a functional difference. The soul insofar as it functions in relation to God can be called the spirit. And the soul in its everyday functions as a rational agent in the world can be referred to as the soul. So we do have a spiritual dimension to our lives in which we relate to God in which we know God in a way that that mere animals don't. But I don't think that that needs to be cashed out in terms of saying that there is an additional thing of which we are composed. Rather this would represent merely a different function of that immaterial part of our being in relation to God. So it seems to me that a basic dualism interactionism of of soul and body is adequate both philosophically and biblically. Thank you for being with us this morning. The next time we meet we'll move on to the topic of the origin of the soul. Meanwhile, stay safe.
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The copyright for the preceding material is held by Dr. William Lane Craig. For more go to reasonablefaith.org.