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Do Benjamin Libet’s Experiments Show that Free Will Is an Illusion?

Michael Egnor

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Materialists often invoke the experiments of Benjamin Libet when they deny free will. Libet was a neuroscientist at the University of California at San Francisco during the latter half of the 20th century who did pioneering research on the neurobiology of consciousness. 

Specifically, Libet was interested in the correspondence of electrical signals from the brain (measured by electrodes taped to the intact scalp in awake volunteers) and the contents of consciousness. His most famous experiments involve measuring electrical activity in the brain when volunteers were asked to move their wrist. The volunteer would look at a moving clock and note the exact time (to the millisecond) that he consciously decided to move his wrist. Libet compared the timing of the brain activity with the timing of the volunteer’s decision to move. He consistently found that the brain activity (he called it the readiness potential) preceded the conscious awareness of a decision to move by a couple hundred milliseconds. The timing typically went like this:

Readiness potential… 400 milliseconds… awareness of intent to move… 200 milliseconds… move wrist.

Other researchers have repeated Libet’s experiments, with similar results, and recently researchers have used fMRI to carry out Libet-like experiments. The fMRI studies show that there are often brain activations that precede the conscious decision by several seconds. 

Free will-deniers like Jerry Coyne have cited Libet’s experiments as scientific evidence that free will is an illusion, and that "voluntary" decisions are really generated by electrochemical processes in the brain, without our consent or knowledge. Our sense of free will is thus only a post-hoc belief imposed by our brain, which is really making the "decisions".


The experiments show, then, that not only are decisions made before we’re conscious of having made them, but that the brain imagery can predict what decision will be made with substantial accuracy. This has obvious implications for the notion of "free will," at least as most people conceive of that concept. We like to think that our conscious selves make decisions, but in fact the choices appear to have been made by our brains before we’re aware of them. The implication, of course, is that deterministic forces beyond are conscious control are involved in our "decisions", i.e. that free will isn’t really "free". Physical and biological determinism rules, and we can’t override those forces simply by some ghost called "will." We really don’t make choices — they are made long before we’re conscious of having chosen strawberry versus pistachio ice cream at the store.

On this, materialists such as Coyne couldn’t be more wrong. 

Libet himself was a strong defender of free will, and he interpreted his own experiments as validating free will. He noted that his subjects often vetoed the unconscious "decision" after the readiness potential appeared.


Do we have free will? 

I have taken an experimental approach to this question. Freely voluntary acts are preceded by a specific electrical change in the brain (the ‘readiness potential’, RP) that begins 550 ms before the act. Human subjects became aware of intention to act 350-400 ms after RP starts, but 200 ms. before the motor act. The volitional process is therefore initiated unconsciously. But the conscious function could still control the outcome; it can veto the act. Free will is therefore not excluded. These findings put constraints on views of how free will may operate; it would not initiate a voluntary act but it could control performance of the act. The findings also affect views of guilt and responsibility. 

But the deeper question still remains: Are freely voluntary acts subject to macro-deterministic laws or can they appear without such constraints, non-determined by natural laws and ‘truly free’? I shall present an experimentalist view about these fundamental philosophical opposites…

Potentially available to the conscious function is the possibility of stopping or vetoing the final progress of the volitional process, so that no actual muscle action ensues. Conscious-will could thus affect the outcome of the volitional process even though the latter was initiated by unconscious cerebral processes. Conscious-will might block or veto the process, so that no act occurs. 

The existence of a veto possibility is not in doubt. The subjects in our experiments at times reported that a conscious wish or urge to act appeared but that they suppressed or vetoed that. In the absence of the muscle’s electrical signal when being activated, there was no trigger to initiate the computer ‘s recording of any RP that may have preceded the veto; thus, there were no recorded RPs with a vetoed intention to act. We were, however, able to show that subjects could veto an act planned for performance at a pre-arranged time. They were able to exert the veto within the interval of 100 to 200 msec. before the pre-set time to act (Libet et al., 1983b). A large RP preceded the veto, signifying that the subject was indeed preparing to act, even though the action was aborted by the subject…

The role of conscious free will would be, then, not to initiate a voluntary act, but rather to control whether the act takes place. We may view the unconscious initiatives for voluntary actions as ‘bubbling up’ in the brain. The conscious-will then selects which of these initiatives may go forward to an action or which ones to veto and abort, with no act appearing.

Libet even observed that his experimental confirmation of free will accorded with the traditional religious understanding of free will:

This kind of role for free will is actually in accord with religious and ethical strictures. These commonly advocate that you ‘control yourself ‘. Most of the Ten Commandments are ‘do not’ orders.

How do our findings relate to the questions of when one may be regarded as guilty or sinful, in various religious and philosophical systems? If one experiences a conscious wish or urge to perform a socially unacceptable act, should that be regarded as a sinful event even if the urge has been vetoed and no act has occurred? Some religious systems answer ‘yes’… But any such urges would be initiated and developed in the brain unconsciously, according to our findings. The mere appearance of an intention to act could not be controlled consciously; only its final consummation in a motor act could be consciously controlled. Therefore, a religious system that castigates an individual for simply having a mental intention or impulse to do something unacceptable, even when this is not acted out, would create a physiologically insurmountable moral and psychological difficulty… 

Indeed, insistence on regarding an unacceptable urge to act as sinful, even when no act ensues, would make virtually all individuals sinners. In that sense such a view could provide a physiological basis for ‘original sin’!

Libet concludes:

My conclusion about free will, one genuinely free in the non-determined sense, is then that its existence is at least as good, if not a better, scientific option than is its denial by determinist theory. Given the speculative nature of both determinist and non-determinist theories, why not adopt the view that we do have free will (until some real contradictory evidence may appear, if it ever does). Such a view would at least allow us to proceed in a way that accepts and accommodates our own deep feeling that we do have free will. We would not need to view ourselves as machines that act in a manner completely controlled by the known physical laws.

Coyne and his allies misrepresent Libet’s findings. Libet concluded from his experiments that we do have free will — the ability to veto pre-conscious intentions — and he noted that the veto appeared to be freely chosen, without any neurophysiological evidence for neurophysiological determinism. 

Libet’s finding that there appear to be pre-conscious intentions that sometimes precede conscious intentions is unsurprising. We experience such intentions constantly. We walk from place to place without consciously thinking of the intricate details of the walk — the path, the coordination of muscles, etc. We often get where we’re going with remarkably little conscious attention to the process — think of how often you drive home from work without consciously thinking much about the route, or even about other cars, traffic signals, etc. When we type, as I am doing now, we typically don’t think about the individual motion of our fingers. In fact, performing a skillful act like typing or playing a musical instrument or driving requires that our actions be automatic and unconscious. That doesn’t mean that our typing or walking or driving is not freely chosen. It means that much of our deliberate behavior is the result of a combination of a free choice to act and an elaborate preconscious and unconscious system of intentions that enable the freely chosen act to happen efficiently. 

Libet proposes (based on his work) a common-sense model of free will: our unconscious is a bubbling sea of velleities. We freely choose the impulses we wish to enact by prescinding from a veto, and we freely choose the impulses we wish to suppress by vetoing the act. Libet found experimental traces of the unconscious impulses (the readiness potential) and experimental confirmation of the freely chosen veto (the conscious choice unaccompanied by corresponding electrophysiological activity). He even noted that his experimental results validated a particular traditional religious understanding of moral choice — that sin is in the act, which is freely chosen, not in the temptation, which can arise without our choice. He even proposed a neurophysiological model of original sin!

You may ask, at this point: why do Coyne and other materialists utterly misrepresent Libet’s experiments? Why would materialists cite the work of a researcher who scientifically confirmed free will, and even confirmed the traditional religious view of culpability? Why would materialists cite experiments that confirm the opposite of their claims? Perhaps materialists don’t understand the science, or perhaps they never bothered to try. 

Whatever their reason for misrepresenting Libet’s work, materialists’ invocation of research that validates free will is likely a consequence not of their acquaintance with the science itself (Coyne seems blissfully unaware of Libet’s actual experiments and conclusions), but a consequence of the metaphysical biases that materialists bring to the issue. You can see the same metaphysical bias and denial of the plain implications of the science in their denial of teleology in evolutionary biology. 

For materialists, it’s metaphysics first, and evidence later, if at all.

Image: Culture of rat brain cells stained with antibody to MAP2 (green), Neurofilament (red) and DNA (blue)/Wikicommons.

Michael Egnor

Senior Fellow, Center for Natural & Artificial Intelligence
Michael R. Egnor, MD, is a Professor of Neurosurgery and Pediatrics at State University of New York, Stony Brook, has served as the Director of Pediatric Neurosurgery, and award-winning brain surgeon. He was named one of New York’s best doctors by the New York Magazine in 2005. He received his medical education at Columbia University College of Physicians and Surgeons and completed his residency at Jackson Memorial Hospital. His research on hydrocephalus has been published in journals including Journal of Neurosurgery, Pediatrics, and Cerebrospinal Fluid Research. He is on the Scientific Advisory Board of the Hydrocephalus Association in the United States and has lectured extensively throughout the United States and Europe.