The Table Video

Richard Swinburne

Implausibility of Physical Determinism

Emeritus Nolloth
 Professor of the Philosophy of the Christian Religion, University of 
Oxford
September 6, 2012

Dr. Richard Swinburne explains why a theory of neuroscience built on physical determinism is both implausible and ultimately unprovable. Dr. Swinburne takes his audience through careful logical scenarios to arrive at his conclusion. Following his argument, two philosophers offer their own comments on Dr. Swinburne’s conclusions.

Transcript:

Physical Determinism. Physical determinism is the doctrine that everything that happens, every event is fully caused by some earlier physical event in accordance with some law of nature. By an earlier event fully causing a later event, I mean that the earlier event necessitates the later event. Not merely makes it probable that it will occur. In philosophical terminology, the earlier event is a sufficient condition of the occurrence of the later event.

If physical determinism were true then every movement we make, everything we try to do, every thought and feeling we have would have been predetermined by events long before we were born, indeed by the structure of the Big Bang which many physicists believe the universe began with or if the universe didn’t have a beginning, eternally predetermined. But I’ve used this term physical event, what is a physical event?

Well, this word like most of the words that are used in this field can be used in various ways but I’m understanding it and the most useful way to understand it is as a public event, an event equally accessible to all investigators. There’s then a contrast between a physical event and a mental event. And the mental event is one to which one person, the person whose event it is has privileged access.

More precisely, I suggest that we call an event in a mental event if and only if whatever ways other people have about learning whether it occurs it’s subject necessarily has an additional way by experiencing it of discovering this. By this criterion, when you feel pain, when you have a mental image, when there’s a pattern of color in your visual field, these are sensations and they’re all mental events. They’re mental event because whatever way someone else has them finding out whether or not you have a pain, studying or behavior perhaps or even your brain events, you have a further way by actually experiencing it. So that’s a mental event.

But by contrast, a physical event such as their being here electrum or the sun shining out there, these are physical events in the sense that whatever ways you have of finding out about them, anyone else can find. There is no superior person who can find out better about them than anyone else. Among physical events are brain events, events going on in your brain. For example, that a certain neuron is firing, that it firing, that is transmitting an electrochemical impulse to a neighboring it in neuron.

This is something we’re all able to discover at least after having had a neuroscientific education. According to the physical determinist which is not merely physical events but mental events which are fully caused by physical events. And it’s not merely sensations so I’ve mentioned pains and patterns of color in your visual field, it’s not merely sensations which are mental events but intentions, beliefs, thoughts and desires. Not all of these events which I’ve just mentioned are ones of which we’re currently conscious.

But what makes the mental events is that their owner can become conscious of them and others cannot. When we’re actually conscious of a mental event it is what I shall call a conscious event. Intentions, by an agent’s intention, I mean the intention in what the agent is doing or trying to do guiding or trying to do his or her movements. My intention in moving my hand is to draw your attention to a philosophical point, my intention in coming to Los Angeles was to give these lectures and so on. It seems to us that our intensions, what we are trying to do make a difference to what we do. My intention to wave my hand caused me to move my hand, my intention to come to Los Angeles caused me to get on the airplane.

Which movements we make often depends, it seems to us not merely on our intention but also on our beliefs. My intention to come to Los Angeles did not by itself cause me to get onto a particular aeroplane, it did so only because I had a belief that that particular aeroplane was going to Los Angeles. There are what are called basic actions. Actions we just do not in virtue of any belief about how to do them, I just do move my hand, I don’t need a belief about how to do it in order to do it. Intentions them and beliefs and these we believe cause us to do what we do. Sometimes we don’t need a belief, we just do it.

Other times we do need the belief in order that our intention may produce a series of actions which will realize that intention. I have privileged access to my intentions and beliefs as my hand moves it certainly seems to me that I am moving it but of course sometimes our nerves get out of control and their hands may move without our intending it. Nevertheless, I can know better than you whether I am intending it to move or not. And clearly the same non basic action such as getting onto an aeroplane may be caused by different combinations of intention and belief. For example getting onto the aeroplane may be caused by my intention to go to Beijing and my false belief that that particular aeroplane is going to Beijing.

But I can know better than you which combination of intention and belief I have. And that’s what makes intentions and beliefs mental events. You may think you can read somebody’s intention of the way their body moves and so on but it’s always the case that particular movements that someone makes are maybe brought about by one combination of intention and belief on another one and the agent can always now or so it seems better than you which combination is at work. So intentions, beliefs these are mental events in my sense. My intentions of course operate through my brain and so if my intention causes my hand to move, it does so by causing a brain event which in turn causes the hand movement.

And so, more generally all our mental events which affect our bodies do so via affecting our brains or at least so it seems to us. So we have these mental events, some of them are conscious. You can’t have a thought without being conscious of it but on the other hand you have all sorts of beliefs, you’re not conscious of but they’re nevertheless mental events because you can become conscious of them and you can know better than anybody else what they are. So mental events, physical events, it seems to us we’re inclined to believe our mental events influence our physical life and the movements of our bodies, the noises that come out of our mouths, these are caused by our mental events.

And that’s the way it seems initially. But the physical determinist tells us otherwise. The physical determinist is committed in this area of the mental life to a doctrine called, epiphenomenalism. Epiphenomenalism, this is the theory that although brain events cause mental events goings-on in the brain cause my intentions according to him, mental events never cause brain events or any other physical events. What happens when, for example, someone forms an intention to move their hand is according to the physical determinist that some brain event caused the intention and the same brain event caused the motion of the hands and that leads the subject to believe that his intention caused the motion of the hand and that according to epiphenomenalism is false. Let’s just illustrate this by a little diagram.

Here is some brain state or rather the physical determinist says this causes my intention, M for mental B for brain. We normally think that even if that is the case even if a brain event were to cause an intention, I didn’t write the intention, possibly with a belief causes a brain event which in turn causes a bodily movement, movement of my hand. But says the epiphenomenalist and the epithets, the consequence of physical determinism it’s not like that at all, the mental event doesn’t do anything. A series of brain events causes my bodily movement. Coincidentally they cause my intention to move my hand, this series causes the hand to move, but this gives me the false idea that it’s really my intention that’s causing the movement of my hand but it isn’t, says the physical determinist. Such is the doctrine of physical determinism.

Now you will know that it’s widely believed that quantum theory, one of the two great physical theories of the 20th century, rules out physical determinism. It is a consequence of quantum theory that the position and motion of a particle cannot be measured simultaneously to a joint accuracy of greater than a certain very small amount H over 4pi.

And since the future position of a particle is a function of its present position of momentum, there is therefore a limit to the accuracy with which the future position and momentum of a particle can be predicted. This result, the Heisenberg indeterminacy principle follows from the basic structure of quantum theory and is well confirmed independently. And what goes for the motion of a particle goes for all small scale phenomena.

Most physicists hold that the data explained by quantum theory could not be explained nearly as well by any deterministic theory. And so they hold that on the small scale, not merely are events not totally predictable but they’re not totally determined. There is for example, it’s normally believed by most physicists that only a physical probability, say of a 1/2 or two-thirds, that a photon, particle of light, emitted from a source of light in the direction of a screen with two slits, there’s only a probability of a 1/2 or 2/3 that it’ll pass through that slit and a probability of a 1/2 or a 1/3 the little pass through the other set. And there’s only a probability that some carbon-14 atom will decay within 5,600 years of a 1/2.

Normally, these small-scale indeterminacies average out on the large scale. Although it’s only for again individual atom of carbon, there’s only a probability of a 1/2 that that atom will decay within the 5,000 year period. Nevertheless, it follows from that. Though it is enormously probable that a proportion very close to a 1/2 of the atoms in a large collection of carbon-14 atoms will decay within 5,000 years. A lump of carbon-14 is therefore what I may call, an averaging system. The undetermined variations of the times at which individual atoms decay gets averaged out. So a large-scale behavior of the lump is almost deterministic. That is varies from the average only by a miniscule amount.

And so of course almost all large-scale systems are almost deterministic and that’s why we can make predictions about the behavior of large-scale systems. But there can be systems in which small scale indeterminacies have large effects. One could for example construct an atomic bomb such the whether it exploded depended on whether some atom in a block decayed within an hour or so. Such a system I will call a multiplying system, it multiplies effects. For these reasons, it might seem that science constitutes no threat to our ability to mold our behavior in the light of our beliefs and intentions for we could make a difference to what happens in our brain and so to the bodily movements we make within the range over which quantum theory does not dictate what will happen.

Note however, that if that was our only reason, if that was our only reason for believing that our intentions cause our bodily movements, our belief would depend on the physicist not discovering some more probable deterministic explanation of the data explained by the laws of quantum theory. And some physicists have tried to produce deterministic theories which as it were are an improvement on quantum theory.

So far they haven’t been successful but it could happen although it’s not very likely. Still at the given time, at any given time, we must believe what is most probable on the evidence available at that time and that is that quantum theory is true and that has the consequence that no small scale events are fully determined. Yet even given quantum theory, it is open to question whether the brain is an averaging device or a multiplying device.

For only in the latter case could some small-scale brain event, for example one neuron transmitting enough of some chemical to the next neuron to cause it to fire, only in the latter case, only if the brain is a multiplying device rather than averaging device could some small-scale brain event cause some bodily movement which would not otherwise have occurred. As far as neuroscientists are concerned this is an unresolved issue.

They don’t know whether small events in the brain could produce very large scale events such as bodily movements very often or not. But on the whole, they incline to the view that wouldn’t happen too often, at least that’s the present state of things. And anyway they also claim that other recent, many neuroscientists also claim, that other recent experimental work gives strong support to epiphenomenalism and so to the view that even if there were a significant amount of indeterminism in the operation of the brain and so it was by no means a deterministic machine. Even so, our intentions make no difference to what happens there and so to our bodily movements.

And so they would say if there is no sufficient cause of some brain event or sequence of brain events for quantum reasons, in that case the neuroscientist would say mere chance determines what happens. And so they claim, even if physical determinism is false it’s crucial consequence of importance for humans for epiphenomenalism is true. So I mentioned that only to point out that quantum theory isn’t crucially relevant to this issue because some more recent neuro scientific work suggests that well, even if quantum theory were true and there’s a certain amount of indeterminism and the brain nevertheless what happens in the brain is uninfluenced by our mental life.

And I’m going to describe this work to you and then I’m going to show why it doesn’t quite show what some people of thought it shows. The recent neuro scientific work on whether our intentions cause brain events and thereby bodily events began with an original experiment in the 1980s by Benjamin Libet. Libet sat many subjects, they were students, at desks in which there was in front of them a very fast clock. In front of each of the subject set a large number of desks. He attached to their skulls an apparatus which would measure any buildup of electrical potential at crucial points on their skull.

He then asked them to move their hand at a moment of their own free choice at some time during the subsequent 20 seconds and to note the time on the clock at which they formed the intention to move their hand. Libet then discovered that there was always a buildup of electric potential 1/2 a second before the time at which according to each subject they formed the intention to move their hand. What this showed, according to many neuroscientists, is that the brain had already determined in advance when a subject would form a certain intention. And had also predetermined in advance that the hand movement would occur 200 milliseconds, that is 2/10 of a second after the formation of the intention.

So it was claimed the experiment showed that intentions don’t cause the brain events which cause bodily movements. That is to say, they sat students at the desks and they said, it’s up to you in the next 20 seconds, some time rather you’ve got to suddenly form and you’ve got to suddenly decide, form an intention to move your hand. And what was found is this series of events that 1/2 a second, roughly, before the student decided to move his or her hand, there was the buildup of potential, build-up electrical charge build-up.

And then, RP it’s often called, and after that 1/2 second later, students reported by watching this very fast clock that they had formed an intention. And then after that 2/10 of a second later, there was a brain event which caused a bodily movement. So first buildup of potential then intention then moved the brain event which started the bodily movement. And they interpret through to that as saying, well, there must have been this first brain event which gave rise to the RP and then that must have been in track causing the bodily movement and this intention which happened after that would also been caused, they guessed, by the brain event and wouldn’t have had anything to do with the bodily movement at least.

So that is the way they interpreted or many neuroscientists have interpreted those experimental results. And those experimental results have been developed by many more sophisticated experiments, many experiments which rely on a knowledge of what’s happening in the brain of a more refined kind than can be got merely from studying the potential on the skull. But of course, this sort of experiment showed no such thing as it was purported to share because it’s perfectly compatible with the experimental results, this sequence of events to suppose that the brain event here which cause the build-up of the potential also cause the subject to form the intention yes, but that the intention caused the bodily movement because you will still get the same sequence of events.

First, buildup of potential caused by some brain event then intention then bodily movement whether or not it’s that way or whether as we normally suppose, it’s that way. So compatible with the data, you could suppose that the brain event cause the build-up of the electric potential and this cause the subject to form the intention but the intention cause the brain event which cause the hand movement. However, these kind of experiments might seem to have opened up the way to the possibility of more sophisticated experiments sharing what this particular experiment, in my view, failed to show.

For it might be suggested, could not the neuroscientists discover that the train of events from the original brain event which form the electric potential, train of brain events from there to the movement of the hand, couldn’t it be shown that that train of events caused, sorry, couldn’t it be shown that the neuroscientists come along and eventually show that maybe there is a train of brain events which starts from here and ends up with the bodily movement.

And couldn’t he also show that this sequence of events occurred whether or not someone formed an intention. So perhaps the scientists can have this plan, he can find out that there is such a sequence of events and then perhaps he could find out that so long as he started his sequence off by prodding some electrode into the brain and pressing a lever, it start the sequence off and it led to the bodily movement. And couldn’t he perhaps prove that this would happen whether or not someone formed an intention, that the intention made no difference to it. So here is a program for the neuroscientists to perhaps to set about and prove what the original experiment seemed to be certainly not to approved.

So isn’t a danger that this sort of thing might be proved. And to generate, there is a program here. So could not such work finally establish epiphenomenalism. Now I don’t wish to deny that sometimes we make bodily movements very quickly in response to some sensory input and only afterwards do we attribute to ourselves some intention in making them. That’s to say we rationalize our actions. When for example you put your hand on the hot plate and sudden they withdraw it, you’re asked afterwards why did you do that and you say because it felt painful, that might be a retrospective description of your action whereas in fact it was so spontaneous that you didn’t have time to form an intention. So sometimes quite clearly we do react in ways which just automatic and don’t involve deliberate intention. But what is at stake in these experiments is whether this is always the case.

Whether for example when you decided to come to this lecture this evening and believe that the lecture would take place here, it was your intention and your belief which caused the motion of your legs to bring you here. For if epiphenomenalism were universally true, your intentions and beliefs would have had no effect whatever on your brain and so on your bodily movements. I shall now argue that no experimental results of this kind, not merely, no present experiments do show this but that no experimental results that this kind could possibly be generalized so as to show universal epiphenomenalism.

But for this purpose, I need to establish a certain result which I will then apply to our subject matter. So follow me during what might seem a digression. It might you won’t see the point of what I’m going to say for the next 10 minutes or so for the moment. Just be bare with me and then I’ll bring it back on to this subject matter.

So follow me during what might seem to be a digression. To establish a scientific theory, and this is a scientific theory. It’s a scientific theory about what causes what. To establish a scientific theory, a scientist needs to show that the theory predicts certain events not predicted by rival theories and that these events occurred. How does a scientist know that certain events have occurred? Well, either the sub scientist is currently observing them herself or remembers having observed them or has had reports from others that they have observed them.

These three sources of our knowledge about particular events, one’s own experience, one’s memory, one’s testimony from others provide the evidence that the events predicted by a theory occurred or rather since all of these sources may mislead it is apparent memory, apparent experience, apparent memory and apparent testimony which provide the evidence that the events predicted by the theory occurred.

Now it’s a fundamental epistemic principle which I call the principle of credulity, credulity, that what we seem to, that is apparently experience, is probably so there in counter evidence by encounter evidence. This applies to what we seem to observe in the public world, what we seem to experience as conscious events and the logical consequences that we seem to see follows from what we seem to apparently remember having experienced. Principle credulity, it says you should believe that things are as they seem to be. So if it seems to you that you’re listening to a lecture, you should believe you’re listening to a lecture in the absence of counter evidence that eventually you wake up and find it was all a dream.

If it seems to you that you’ve worked out a piece of arithmetic and it comes to the answer 275, you should believe the answer is 275 unless you’ve got any reason to suppose you’ve made a mistake and so on and so forth. And the consequence of this is that it seems to you you’re experiencing something, now you should believe you do if it seems to you that you apparently remember something, you should believe you do in the absence of reason to suppose you’ve made some mistake and generally so. And it’s the second fundamental epistemic principle which I call the principle of testimony that what people seem to be that is apparently are telling us that they experienced they probably did experience again barring counter evidence. Somebody tells you they’ve been to London, they saw so-and-so outside, etc, other things being equal, you should believe that that’s the case.

If that seems to you, if either of these principles seem to you as it were over credulous then reflect on the consequences of not believing them. If you say, oh, you shouldn’t really believe my experience unless you check it out, well, alright, check it out and then should you believe your experience, well you want to say yes but then you’re relying on the memory that it seems to you that you’ve checked it out. So unless you’re justified in believing that that, you shouldn’t rely on strong experiences but in that if you are justified in believing that then you ought to be justified in believing any apparent seeming if in the absence of counter evidence.

And likewise, if you think oh, shouldn’t believe anybody testimonies or anything they say to you unless you’ve checked it out, well if you really think that, you wouldn’t be justified in believing anything that anybody tells you about history or geography or anything else apart from your own immediate experience because you can’t check all these things out. And in fact we think it perfectly reasonable to do so. So rational, it’s rational to believe that things are as they seem to be as you seem to remember them as people tell you. These are basic principles and principles on which science relies. Science relies on its evidence or the scientists taking his apparent observations, experiences and calculations as probably correct at least when he’s looked carefully and checked. Almost all scientific knowledge relies on apparent memory.

For example of the results of experiments or calculations written up only the following day. And for all science we rely most of the time on the apparent testimony, written and spoken, of observers to have had certain experiences, our theoreticians to have done certain calculations. And the wider public relies entirely on the apparent testimony of Starsia scientists with respect both to their calculations and to their experiences. Beliefs acquired by apparent experience, memory and testimony are however open to counter evidence or defeatist.

That is one can have evidence that despite the apparent experiences or whatever, the resulting beliefs are not to be trusted. One kind of defeater is an undermining defeater. If someone has had an apparent experience of an event X which would make it probable that some other event Y occurred, an undermining defeater is any evidence which makes it probable that X didn’t occur or isn’t good evidence for Y. An undermining defeater to a belief in Y doesn’t show that Y didn’t occur, it merely shows that our supposed evidence X is not a good evidence for supposing that Y did occur. The evidence constituting the defeater however, must itself be provided by apparent experience, memory or testimony.

In relying on evidence for the occurrence of some event provided by apparent experience, memory or testimony, we assume that the occurrence of the event cause the apparent experience, testimony or memory. And if we have evidence that it didn’t, then that constitutes an undermining defeater for the belief that the event occurred. For example, suppose I [mumbles] to belief that my telephone is ringing because I apparently experienced hearing my telephone ring. And then someone points out to me that the noise is coming not from the telephone but from the television set where someone is depicted as hearing a telephone ring.

That constitutes an undermining defeater for my belief resulting from apparent experience that the telephone was ringing. It doesn’t show that my telephone was not ringing but it does show that the noise was not evidence that it was because the noise had a different cause. So if it seems to you, you’ve seen something and then somebody points out to you, you’d have had that experience anyway of whether or not that something has occurred because the variance had a different cause that undermines your justification for supposing that the experience was of what it seemed to be. A similar assumption of the existence of causal chains, although longer causal chains, then for immediate experience such as in the telephone case, and ones involving different kinds of events undergirds our belief in the deliverances of apparent memory and testimony.

I trust my apparent memory of an event because I assume that that apparent memory was caused by a past apparent experience of the event recalled. And I assume that that experience was itself caused by the event thus entrusting my apparent memory that I visited young London when I was five years old. I assume that the apparent memory was caused by my apparent experience of being in London when I was five years old. And that that experience itself was caused by my being in London then. Hence the generally accepted causal theory of memory. Any evidence that the apparent memory was planted in me by a hypnotist or a brain surgeon constitutes an undermining defeater for that apparent memory belief.

So too does any evidence that my apparent memory was caused by my reading a fictional story written by my father in which I visited London. Similarly, in believing someone’s apparent testimony to be experiencing or have experienced some event, I assume that they say what they do because they are apparently experiencing or apparently remembered having experienced that event and have the intention of telling me the truth about it.

That is their apparent experience or memory and their intention causes them to say what they do. Causes in the sense of being a necessary part of the total cause. In the case of a past event, I believe that there are apparent memory, the apparent memory of someone who tells me he experienced that thing, I believe that their apparent memory was caused by an apparent past experience of the event, the latter are being caused by the event itself.

So if I get evidence that the words coming out of some persons mouth were not caused by any intention of his, that is that the words were caused by a neurophysiologist stimulating that person’s neurons to cause his mouth to make the sounds or simply as in fluent aphasia where a neural malfunction causes a stream of words to come out of the subjects mouth. That evidence constitutes an undermining defeater to belief in the truth of what the person seemed to be saying. It’s a long sentence, I’ll [mumbles] the idea.

If words come out of somebody’s mouth and it seems to you they’re telling you something but it then turns out some hypnotist is in fact manipulating their brain or simply that their brain has gone on automatic behavior and is producing noises quite independent of their intention, then you wouldn’t believe what they’re saying because that’s an undermining defeater because it’s shown that apparent testimony isn’t real testimony. In all these cases, the counter evidence in the form of an undermining defeater must itself come directly or indirectly from apparent experience memory or testimony. So in summary what I’ve been saying for the past 10 minutes, science relies on an epistemic assumption, EA, as I call it. First that a justified belief in a scientific theory requires a justified belief that the theory makes true predictions.

Secondly, a justified belief that the theory makes true predictions is provided by and only by evidence of apparent experience memory and testimony that the theory predicts certain events and those events occurred. And thirdly such justification is undermined by any evidence that any apparent experience was not caused by the event apparently experienced, any apparent memory was not caused by an apparent experience of the event apparently remembered and any apparent testimony was not caused by the testifiers intention to report his apparent experience or memory. These three points I’m calling EA. I hope that the few examples by which I have Illustrated its application show the centrality of EA in our noetic framework.

The fundamental criterion, which I call FC, lying behind EA is that justified belief that some event occurred requires the assumption that the event is privilegedly accessible to you, to the believer or causes effects privilegedly accessible to the believer. That’s to say you believe what you do because either you’re experiencing yourself or you believe the belief is ultimately caused by the event which you believe either caused because you’re seeing it’s in the outside world or caused by your memory of it or caused by somebody’s testimony to their memory of it. You assume there’s a causal chain from whatever events you believe occurred to your present belief. If you find that isn’t the case then you see your belief is not justified.

Now, if you’ve been with me for the last 10 minutes, back to this. Now, I noted earlier that what a neuroscientist would need to do in order to show that our intentions do not cause our bodily movements is to produce a train of events from before the time when the subject formed their intention from B1 to the bodily movement and to show that this train of events would occur whether or not the subject formed the intention to make that movement.

If the scientist could produce that evidence, then that would show that the intention was irrelevant to whether the bodily movement would occur and made no difference to it but mere brain events caused him. But in order to show this, he would have to show that this happened whether or not the subject forms intention.

And in order to show that, the neuroscientist would need to know just when subjects formed the intentions that they did and how is the experimenter to find this out. Well, as in the Liberty experiments and inevitably because they depend on what the subjects tell them about when or whether they form intentions. But why should the scientists believe what subjects, students sitting at desks, tell them about when they form intentions? Well, he believes them because he thinks that they have the intention of telling him the truth and the belief that they formed the intentional when they said they did.

The experimenter believes the students and he believes the students because he believes students are trying to tell him what’s going on in their mind and that the students words, I formed this intention at exactly 2 o’clock, is coming out of their mouth because the student has the intention that they should come out of their mouth and the belief that that was when he formed the intention and the words come out of the mouth because of his intention that they should. The scientist believes what the students say because he thinks they have the intention of telling him the truth and the belief that they formed the intention when they said they did.

I have however just pointed out that we believe what people tell us because we believe that they are saying what they do because their intentions and beliefs cause them to say what they do. But if universal epiphenomenalism were true, then the words would come out of subjects mouths not because the subjects formed the intention that they should come out of their mouth but simply because certain brain events caused those most words to come out of their mouths.

The situation would be the same, situation of the students saying, I formed the intention at this time, would be the same as in fluent aphasia or Tourette’s syndrome when words come out of a subjects mouth but we know that the words are formed by some brain processes which is not the result of any intention on the subjects part to intent and utter those words. It is a necessary condition for a justified belief in what people tell us that we believe what they say is caused by their intention to tell us what they believe. So the situation is that epiphenomenalism could only be shown to be operative in a particular kind of case e.g. in the experiments that Libet was doing.

He could loose the experiments could only show that in those cases epiphenomenalism was operating on the basis of results which could only be trusted on the assumption that epiphenomenalism is false for some other kind of situation. For example, in respect of the words which come out of the subjects mouth when they tell us about their intentions. So there is absolutely no possibility of a universal epiphenomenalism being established by this route because you can only get the evidence which would show it to be true on the assumption that the way which provided the evidence assumed that epiphenomenalism was false. So it’s self-defeating in this way.

So any attempt to establish universal epiphenomenalism by this sort of route, by showing the brain processes cause bodily movements and the intentions don’t make a difference to them is bound to be self-defeating, I mean when it shows that certain sorts of actions we do have this characteristic. But only on the assumption that generally that isn’t the case. As I say, it couldn’t show that always this is the case because it couldn’t have any evidence for it because if it was always the case, then you couldn’t trust a word anybody told you about when they formed their intentions. Now that’s not quite the end of the story because you might think that Universal epiphenomenalism could be established in a different kind of way.

Not by showing what happened in our mind was irrelevant to physical processes but by showing that physical processes were totally deterministic and therefore what happened in our mind couldn’t make any difference to what happened because we had a total theory of what happened which didn’t bring that in. That is to say you could try and establish it without relying on evidence which comes from people’s minds.

Now, I drew attention earlier to the suggestion that quantum theory might one day be superseded by a successful determinist theory. Such a theory would have the consequence, if it were established, that every physical event and that will include every brain event had as an immediate necessary and sufficient condition of its occurrence another physical event. If this was shown, then of course no mental event could make any difference to what happened in the brain.

But a similar problem with the justification of that all-embracing physical theory would arise. In order to be justified in holding the theory, we would have to know that it makes successful predictions. In this case, we might discover that various, in this case which would be different from the earlier case, we might discover that various events purportedly predicted by the theory did in fact occur without assuming that mental events cause physical events. For someone’s observation of a physical event might cause a trace in their brain which in turn caused the words to come out of their mouth reporting the occurrence of the event without the causal came proceeding through any mental event.

That one could imagine that as it were the scientists who studied goings on in the lab which was supposed to be evidence for physical determinism, they observed these [mumbles], they looked at these events and the light from these events landed on their eyes caused disturbances in their brain which caused them to have the belief that the event had occurred without that causing any mental event and therefore causing relying on downward causation from the mental to physical. Well, you could suppose that happened. Subjects would then not be reporting that they observed an event but only that the event happened.

And in a rather stretched sense of testimony, subjects would then testify to the occurrence of the event. But in order for the occurrence of certain events to be evidence supporting along embracing physical theory, we would need to know that the theory predicted those events. To work out what a complicated theory predicts involves a long process of calculation. No individual scientists can hold such calculation in his head, he will need to write it down or type it into his computer the various stages of the calculation. And he will need to believe that he writes it down each line of the calculation because he sees that he has a convinced thought that each line is entailed by the previous line.

That is, he assumes that some mental event of his, a conscious belief is causing via some brain event, his hand to type what he does. And to assume that is to get to assume that mental events cause brain events. And so again, he can only justifiably believe that all physical events are caused by and only by physical events by making the assumption that sometimes they aren’t. And it wouldn’t make any difference if the scientist could do all his calculations mentally. For he would need to believe that the last line of his proof was caused by his beliefs about earlier stages of the proof. And we know that earlier experiences are recalled later because they have been laid down by memory traces in the brain.

And so he would lead, so relying on memory involves relying on conscious experiences causing brain experiences. That is even if the solitary scientist by himself is working out that his theory makes certain predictions, it takes time to work this out, and therefore he relies on his memory of his past calculations to make progress with his future calculations.

But he relying on memory means relying on his past experiences having caused brain events which in turn caused him to have the memory of them but listened again involves assuming that his past experiences do cause brain event. In other words, once again it’s assuming what the theory is trying to prove false. So but if that solitary scientists generator, a rather rare phenomenon, and every scientist rightly relies on other scientists to confirm his calculations. And to do so is to rely on their testimony to their mental events which again involves making the assumption that the mental causes the physical.

And so generally, with respect to any kind of evidence, you could have for physical determinism, the evidence itself can only be trusted on the assumption of physical determinism is false. My argument so far doesn’t prove that physical determinism or its consequence epiphenomenalism is false but it does show that they couldn’t be shown to be true.

I must now take the argument a little further. To have a certain intention to do an act is to try to do that act. And to try to do that act is to do what you believe will bring about the performance of that action. So inevitably when we are acting, we must believe that our intentions do affect our bodily movements. If we didn’t do that, we couldn’t perform any intentional actions at all.

And if it seems to us very strongly for that reason that we do affect our bodily movements by our intentions as when we try hard to do a difficult action, we inevitably believe strongly that we are exerting causal influence. I suggested earlier but it is a bracing principle of epistemology which I called the principle of credulity that probably things are the way they seem to be in the absence of counter evidence.

And if that’s right, then since mental events can only cause bodily events by causing brain events, probably mental events do cause brain events in the absence of counter evidence. What I claimed to have shown is that there could not be counter evidence to universal epiphenomenalism. And since we cannot but believe that our intentions do cause our bodily movements in the absence of counter evidence and since we couldn’t have counter evidence, it is rational to believe that they do, probably things are the way they seem to be, and they certainly seem to be that way, that our intentions cause our orderly movements.

And so the rational conclusion can only be that if we phenomenalism is false, physical determinism is false and in our mental events do as we always suppose they did cause our bodily movements via causing our brain events. And there’s nothing very surprising really about the idea of mental events causing brain events because after all it’s even more obvious that brain event sometimes cause mental events. If you stick a needle in me and it causes are going on in my brain and that causes me to feel pain, there is obviously the upward cause or route of brain events causing mental events. So there’s nothing surprising in there being a connection between the brain event and the mental event.

And if it comes one way, there’s nothing surprising in it happening the other way and my arguments been designed to show that it does happen in the other way. So even if, even if quantum theory were superseded by some other theory of physics, that new theory of physics would also have to allow that the brain is not governed entirely by deterministic physical laws. So physical determinism is implausible. It remains probable that we do what we do because of our intentions and beliefs.

That is because we mean to do it. It is still however possible as far as anything which I’ve argued in this lecture shows that our intentions are themselves fully caused by brain events and so psychophysical determinism as opposed to mere physical determinism is true. And I haven’t given you any arguments as to why I think that it isn’t. But I do have arguments as to why I think that isn’t but alas that must be a subject for another lecture.

But as far as this lecture is concerned, the main threat which neuroscience of recent years has thrown at traditional beliefs that our intentions cause our bodily movements seems to me doomed to failure for this very simple reason that any evidence for it would itself depend on its falsity. And that is my main conclusion. [students applauding]

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