Resolving the question of the existence of ‘free will’ is considered by many as a hopeless task, given that the greatest minds have tried and failed to settle the matter over the last two and a half millennia.

Thus far, philosophers have been the protagonists, but more recently a few biologists and neuroscientists have weighed in. For a materialist, a neuroscientist and an evolutionist, accepting the existence of free will is a rare position and one worthy of special attention as it has become received wisdom to state that free will either doesn’t exist in a fully deterministic universe or that a much attenuated form of free will exists which is compatible with a predetermined universe. As a result, the advocacy for the existence of free will has frequently been the preserve of panpsychists, theologians and those interested in the mysterious and the supernatural.

Mitchell’s declared aim is to ‘naturalise the concept of agency’. He argues that the evolution of life involved more than just the novel arrangement of matter. Thus, even single-celled organisms are imbued with a degree of agency: they act within their environment in pursuit of their own goals, survival and propagation. More complex organisms with brains have reasons for their actions and, in the case of humans, can reflect upon these reasons.

Mitchell renames the hard and soft versions of determinism as ‘physical predeterminism’ (the idea that only one possible timeline exists) and ‘causal determinism’ (the idea that every event is necessarily caused by preceding events), respectively. A third category is ‘biological determinism’ (the idea that an organism’s actions are internally necessitated by its own physical configuration).

He dismisses physical predeterminism and biological determinism which leave no room for randomness by dictating that there can only be one possible future (and in the case of biological determinism by also ignoring the existence of agency). The real existence of randomness in complex systems, specifically in biological systems, provides decisive evidence against predeterminism. The random errors of DNA copying, which contribute to the variation that is acted upon by natural selection, are pivotal to the evolutionary process.

Nevertheless, Mitchell concedes that randomness does not in itself serve to demonstrate the existence of free will but it does provide ‘…a pervasive degree of indefiniteness that loosens the bonds of fate and creates some room for agents to decide which way things go’.

Mitchell makes a strong case against the reductionist position that events at the lowest level of organisation are causally comprehensive. In our view, this is one of the most important messages in the book.

This book should be of interest to reflective psychiatrists whether or not they have a prior interest in philosophical questions. Whether readers agree or disagree with the author’s thesis, they will come away from it better informed about their own position regarding a range of vitally important questions that go to the heart of what makes us human.