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Opinion - NATURE I volume 459 I 25 June 2009

SIR - In his Essay 'Is free will an illusion?' (Nature 459, 164–165; 2009), Martin Heisenberg suggests that belief in free will is supported by quantum events. However, the concept of free will may become confused if it is linked with an absence of determinism.

As an example, let us consider three schoolgirls, X, Y and Z, confronted with the proof of Pythagoras's theorem: X has a talent for mathematics and enjoys working out proofs; Y is weak in this domain and is unquestioning; Z has average ability but her decisions are capricious. The teacher instructs them to believe the theorem because it is correct. Y accepts it immediately, X first confirms for herself that the proof is valid, but Z (possibly influenced by a 'quantum event' in her brain) refuses to agree. Although the behaviour of X and Y is predictable and determined, given their personalities and abilities, Z's is not.

Heisenberg's suggestion would support the conclusion that only Z's decision was 'free'. But X could be judged as the one who made the really free (autonomous) decision. Y's decision is formally free, having been determined by her accepting nature, but it is undermined because it stems from the teacher's authority. Z's reaction is not free at all, because it was not determined by Z herself but by a random event in one or more of her brain cells.

In short, deciding freely does not imply a lack of determinism — rather, it is determined by central aspects of our personality: our long-term needs, the emotions accompanying their non-fulfilment, and our rational thinking about the means to satisfy those needs. Our decisions may therefore not be completely free, because they are not always exclusively determined by these central (core) factors. A person who stops smoking on rational grounds is freer than another who makes a decision to stop but fails to do so.

Quantum events have no relevance here: the question is whether we are influenced more by our core factors than by drives that are not rationally founded, such as habit, addiction or external pressure. Consciousness and the experience of positive or negative emotions could well play a part in our decisions: in my opinion, these are not epiphenomena — mere parallel events — but essential for bringing about determining factors that underlie our free will. This would not exclude a purely naturalistic explanation of the processes that we experience as consciousness.

Etienne Vermeersch

Nature volume 459, pages 1052–1053 (25 June 2009)