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#314 Libet’s Experiments and Determinism

April 22, 2013

Dear Prof. Craig,

what does the Libet-Experiment indicate about free Will?

A US-american Scientist, Libet, conducted in 1979 an experiment involving the measurement of Brain-Activity during a controlled Decision-making Process, in order to better understand relations between neurological (physical) phenomena and the activity of the will.

The observation was, that:
1. brain activity occurs, then after a delay
2. one is oneself aware that a decision has become made, then after a delay (for the body to react)
3. the decision becomes made.

The delay between (2) and (3) can become accounted simply by transmission delays from the brain to the body. Of interest is the delay between (1) and (2).

Some (neurobiologists) claim, the gap between (1) and (2) demonstrates that the brain makes the decision and then the person experiences the decision (and simply associates the decision to his own free doing, as opposed to that of the body).

But a few things do not seem (to me) in order here. E. g.

a. (2) merely marks, when the person is, at another level of awareness so-to-speak, aware of his decision. But making a decision and becoming aware of the same are prima facie distinct phenomen, and thus should not be assumed to occur simultaneously. In order to disprove that a free-will decision has occurred, it seems one would have to collapse these two notions.

b. Assume now, decision-making and awareness of the same were to occur simultaneously. The so-called "readiness potential" in (1) is only measured in the times in a small neighbourhood of the activity. Could it be that this readiness potential regularly spikes, and that this be simply a regular phenomen which puts one into a state to make a decision? In this case, the compatibility of free-will and this preempting brain-activity are perfectly compatible.

My objections aside, I would really like to hear your professional opinion of this.

* The existence of free-will is among the deepest and most difficult problems in Philosophy/Science. If this problem were solved, and the Libet-Experiment were to have conclusively shown that human decision-making is not free but determined, there would then be consensus. Is there Consensus about the interpretation of the observations in the Libet-Experiment? Is there Consensus about the Free-Will Problem?

* What at all possible do the observations of the Libet-Experiment actually indicate?


* Some simply take the approach of redefining free Will as a phenomen, whereby although the decision is determined, its causes is truly the person who does the deciding. In this way, some thing that Determinism is no problem at all for free Will --- rather the definition of free Will could be rethought. What do you hold of this approach?

Thank you for reading and thank you for your work!

With kind Regards,


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Dr. craig’s response


Although Philosophy of Mind is not one of my areas of specialization, Raj, so that I usually refer people with questions like yours to the work of those who do so specialize, like my colleague J. P. Moreland, nevertheless, since the Libet experiments play such a pivotal role in Alex Rosenberg’s defense of naturalism, I did some poking around concerning Libet’s fascinating results in preparation for my debate with Rosenberg.

First, let’s state accurately what Benjamin Libet discovered, since your statement of the three events or stages in the execution of a decision is a bit sloppy and, hence, potentially confusing. In Libet’s initial experiments people were instructed to press a button with one of their fingers while he monitored their brain activity. Libet discovered that prior to a person’s awareness of his decision to press the button, a brain signal had already occurred which resulted in his finger’s later moving. So the sequence is: (1) a brain signal occurs about 550 milliseconds prior to the finger’s moving; (2) the subject has an awareness of his decision to move his finger about 200 milliseconds prior to his finger’s moving; (3) the person’s finger moves.

Now let’s look at your three bullet-point questions. With respect to your first question, there is no consensus concerning the interpretation or significance of Libet’s results. Indeed, they are a matter of considerable controversy. As you might imagine, some thinkers have taken the results to provide evidence for determinism and even materialism. Such an inference is overdrawn. In a second run of experiments, Libet discovered that even after the brain signal fired and people were aware of their decision to push the button, people still retained the ability to veto the decision and refrain from pushing the button! So, as you note in your point (b), some interpreters take the brain signal to indicate but a “readiness potential” to initiate movement which the subject may go along with or cancel.[1] Libet himself considered his experimental results compatible with the existence of free will. Interestingly, Rosenberg, though himself a materialist and determinist, agrees that the experiments do not prove that there is no free will but appeals to them merely to show that we cannot trust introspection to tell us whether or not we have free will. [2]

The more fundamental point, however, seems to me to be your point (a), which serves to answer your second question. As I contemplated Libet’s results, it struck me forcefully, this is exactly what the dualist-interactionist would expect. The soul (or mind) does not act independently of the brain; rather, as the Nobel Prize-winning neurologist Sir John Eccles put it, the mind uses the brain as an instrument to think. So, of course, the soul’s decisions are not simultaneous with the conscious awareness of them. How could they be? Given the soul’s reliance upon the brain as an instrument of thought and the finite velocity of the transmission of neural signals, of course there is a time lag between the mind’s decisions and the awareness of them. In Libet’s experiment, since neural processes travel at finite velocities, of course it takes time for the mind’s decision to come to consciousness. This is exactly what we should expect on a dualist-interactionist view.

The German philosopher Uwe Meixner, himself a dualist-interactionist, makes precisely this point about the Libet experiments. He writes,

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; 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.[3]

Even naturalists get the point, though it is sometimes misexpressed. For example, philosopher of biology Massimo Pigliucci says,

Libet’s experiments. . . demonstrate. . . that we make unconscious decisions. . . ahead of becoming aware that we have made them. I doubt that anyone who has caught a falling object before realising what he was doing would be surprised, and I doubt anyone would seriously take that sort of experience as evidence that. . . consciousness doesn’t enter into. . . deliberative decision making (neither did Libet himself, incidentally). [4]

Similarly, Rosenberg muses, “Maybe the real decision to act that takes place unconsciously really is a free choice.”[5] Such statements, while conceding the dualist-interactionist’s point, seriously misexpress it. The person’s decision is most emphatically not unconscious; it is a conscious decision, but because of the finite velocity of neural signals it takes time for the person to become conscious of it. Just as we never see present events because of the finite velocity of light, but only events just slightly past, so we do not have consciousness of our decisions simultaneously with our making them but unnoticeably afterwards. If the soul has the ability to decide without being causally determined, then, as Meixner says, in order to make free, responsible decisions, the soul just needs to be conscious of the facts relevant to the decision prior to making the decision. So to answer your third question, Raj: there’s no reason here to resort to compatibilist views of free will, which perversely take freedom to be compatible with causal determinism.

Finally, I want to say a word about Rosenberg’s defense of naturalism, given the seemingly absurd conclusions to which it drives him, such as that we never think about anything or that I do not endure through two moments of time or that I do not even exist. Rosenberg tries to save his view from absurdity by claiming that introspection is unreliable, and so all these things are just illusions. The title of his chapter is “Never Let Your Conscious Be Your Guide.” He appeals to Libet’s experiments and experiments demonstrating so-called blindsight in a desperate attempt to invalidate all knowledge acquired via introspection. The Libet experiments thus play a hinge role in his defense of naturalism.

The problem with Rosenberg’s attack upon introspection is that introspection is not intended to be a guide to brain states but to mental states. It tells us how things appear to someone. So in blindsight experiments the person correctly reports, for example, that nothing yellow appears to him. In Libet’s experiments the person correctly reports when he has an awareness of deciding to move his finger. In fact, ironically, these very experiments actually presuppose the reliability of introspection! For how do you know that the blindsighted person has no visual experience of yellow? Because he tells you! How do you know that the person has consciously willed to push the button rather than think about his summer vacation? Because he tells you! These very experiments actually presuppose the veridicality of one’s introspective reports.

So Rosenberg’s critique of introspection is quite fallacious, and all the absurd consequences of his naturalism come crashing in upon him as a result.

  • [1]

     Angus Menuge, for example, writes,

    “if you look at Libet's experiments closely, there was a prior conscious decision by the instructed subject, then a readiness potential, then awareness of that readiness potential, and then a movement. So one can still say that a distal conscious decision was the cause of the movement, even if the proximal cause is the readiness potential” (Angus Menuge, “Does Neuroscience Undermine Retributive Justice?” in Free Will in Criminal Law and Procedure, ed. Friedrich Toepel, Proceedings of the 23rd and 24th IVR World Congress, Kraków 2007 and Beijing 2009 (Stuttgart: Franz Steiner Verlag 2010), preprint.).
  • [2]

     Alex Rosenberg, The Atheist’s Guide to Reality: Enjoying Life without Illusions (New York: W. W. Norton, 2011), p. 154

  • [3]

     Uwe Meixner, “New Perspectives for a Dualistic Conception of Mental Causation,” Journal of Consciousness Studies 15/1 (2008): 25.

  • [4]

     Massimo Pigliucci , “Is Science All You Need?” (June 7, 2012) http://philpapers.org/rec/PIGISA


  • [5]

     Rosenberg, Atheist’s Guide to Reality, p. 153.

- William Lane Craig