The free will fallacy: Libet’s error

Peter MolemanArticles, Complex systemsLeave a Comment

For a long time people have tried to link complex mental processes with specific brain processes. This often leads to misconceptions. One example of this is the idea that there is no such thing as free will. What does the concept of free will mean to us? That we decide for ourselves what we do and what we don’t, that we can choose. And that this is not decided by someone else, or by force of circumstances. The conviction that free will does not exist has gained momentum through Libet’s experiment.

Libet’s famous experiment

The experiment went as follows. Subjects were asked to perform a quick, abrupt flexion of the fingers and/or the wrist. They were free to choose when they did this. Therefore, if they lifted their fingers it was assumed to be of free will. Further, they could indicate when they had decided to lift their fingers. That appeared to be approximately 0.2 seconds before they performed the movement. Libet established that even before this, approximately 0.5 seconds before they carried out the movement, the preparation for the movement was visible in the brain. This was more than 0.3 seconds before they announced their decision to carry out the movement!
Libet determined this with an EEG ( ElectroEncephaloGram), which is a way to measure the electrical activity of the brain. In the premotor cortex (see Figure 2) you can see the readiness potential on the EEG: electrical activity that gradually increases till the moment of motion (Figure 1). This activity is assumed to indicate getting ready for the movement, which explains the name “readiness potential”. Libet observed the start of this activity more than 0.3 seconds before the subject indicated that he had taken the decision to carry out the movement. The preparation for the movement therefore begins before the subject has consciously decided to carry out the movement! The brain has a head start on free will!

Figure 1. Schematic graph of the “readiness potential” in Libet’s experiment

The baseline in Figure 1 shows the time, from 550 milliseconds before till just after the movement onset of the fingers at moment 0 (ms). The red line represents the strength of the EEG signal. The ascending limb starting at -550 milliseconds represents the RP (Readiness Potential). The start of the readiness potential (Rise of RP) preceeds the conscious wish to move (W) by more than 0.3 seconds.

Figure 2. External view of the human brain showing the primary motor cortex (M1) from where motor activity is directed, and the premotor cortex (PMA) where movements are prepared for, and where Libet measured the readiness potential.

Libet’s fallacy

It has taken nearly 40 years to establish that this is not a correct interpretation of the brain activity observed by Libet. The fallacy is to assume that that which takes place first is the cause of what follows. A classic example is, ” Every time after Critias has prayed at the temple of Zeus, he reaches home to find a bag of food on his doorstep. Therefore the appearance of food must be the result of his prayers”1 This does not seem very probable to us. However, the connection between the brain activity and the movement is somewhat more complicated than in the example with Critias, where the arrival of food and the praying are probably unrelated but occurring at around the same time. Whereas the brain activity – the readiness potential – does have a connection with the preparation for the movement. That makes Libet’s reading of a causal association easier to understand. But if the association is causal then this brain activity should always be followed by a movement. Appearantly Libet did not look into this. Only recently have adequate experiments been performed showing this not to be true. Readiness potentials are generated almost continuously in the premotor cortex, and only a few of these lead to an actual movement.

The brain does not decide before the test subject does

One must interpret this potential, shown in the figure as “Rise of RP”, very differently. The brain shows continuous activity which in this case has to do with the decision to lift the subject’s fingers. The preparation for the movement itself is a part of this. In many cases this does not lead to the actual decision to move, in which case the potential decreases, and increases again after a while. Only when the readiness potential reaches a particular threshold value is the movement actually initiated. That moment, the crossing of the threshold value, is approximately 0.2 seconds before the movement, which was exactly the moment when the subjects indicated their decision to carry out the movement2 This is the case in Libet’s experiment. A movement can also take place without a readiness potential preceding it; see Bold et al., which seems to further muddy the waters regarding the relationship between movement and the readiness potential..

Simple experiments and the free will

The conclusion that the brain is ahead of free will is incorrect. Libet’s experiment illustrates that a lack of understanding of complex dynamic systems can lead to erroneous conclusions about the working of the brain3Freeman already knew this 20 years ago, see References. Focusing on one single activity in isolation in an experimental situation can be very useful for our understanding of the workings of the brain, but this can not deliver conclusions about how the brain deals with complex mental processes in real life. Put differently: you cannot assume that research in a laboratory situation into the movement of fingers will provide meaningful information about the free will. Nor how the movement is causally associated with activity in specific parts of the brain. A word of caution: the recent research which I quote and which contradict interpretations of Libet’s findings, are also not to be seen as proof that free will does exist!


Bold J lyn, Mudrik L, Maoz U (2022): How are arbitrary and deliberate decisions similar and different?; in Maoz U, Sinnott-Armstrong W (eds): Free will: philosophers and neuroscientists in conversation. Oxford University Press, ISBN 978-0-19-757218-4, pp 165–174.

Maoz U, Sinnott-Armstrong W (eds.) (2022): Free will: philosophers and neuroscientists in conversation. Oxford University Press., ISBN 978-0-19-757218-4.

Seth A (2021): Being you: the inside story of your inner universe. Faber & Faber. Kindle Edition., ISBN 978-0-571-33773-6, Ch 11.

Schurger A, Hu P “Ben,” Pak J, Roskies AL (2021): What Is the Readiness Potential? Trends in Cognitive Sciences 25:558–570.

Freeman WJ (1999): Consciousness, Intentionality, and Causality. Journal of Consciousness Studies 6:143–172.

Libet B, Gleason CA, Wright EW, Pearl DK (1983): Time Of Conscious Intention To Act In Relation To Onset Of Cerebral Activity (Readiness-Potential): The Unconscious Initiation Of A Freely Voluntary Act. Brain 106:623–642.

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