An internet search for ‘motivation’ produces thousands of hits. Clearly we are fascinated by what makes us tick, but despite the wealth of research there is no consensus. Robert West's Theory of Addiction is a bold attempt to unify our understanding of human behaviour and its pathological refraction that is addiction. As a Professor of Health Psychology, and prolific contributor to the literature on addictive behaviour, West is arguably the man for the job.

After considering the definitions of addiction, West rethinks how we appraise behavioural theories and asks us to use ‘observation of nature’ as a starting point. He argues for a Popperian stance, that a theory is wrong if a counter-example exists, then sets the scene for his own theory with an erudite review of the literature.

The reader is walked through the evolution of his theory before it is introduced as ‘PRIME theory’ (plans, responses, impulses/inhibitory forces, motives and evaluations); a hierarchical representation of the motivational system which serves well as a template for human behaviour despite the unwieldy schematics.

West blends PRIME with chaos theory in a Pythagorean attempt to understand behaviour in mathematical terms. He invites us to think of the motivational system as an epigenetic landscape with hills and valleys (Chreods) through which a ball (time) travels resulting in a number of potential future outcomes depending on its course. He acknowledges the metaphor in applying chaos theory to addictive behaviour and this book joins a growing discourse on the subject. The concept is user friendly and explains why addictions manifest so differently despite often similar underlying pathologies. A strength is that it allows for such variance, but as a result the theory becomes too inclusive for rigorous testing. My limited understanding of chaos theory left me wondering whether human factors such as the capacity for mentalisation might influence its relevance to psychiatric disorders.

In citing economic and neurophysiological theories, the author's intention is that other disciplines could add to the work. It would also be interesting to hear how PRIME interfaces with cultural and psychodynamic constructs. In the closing chapter, West applies his theory to addiction and suggests approaches for intervention that I would like to have heard more about, such as how one might detect an imminent Chreod bifurcation.

In the end I felt that, in addition to PRIME theory, the book had introduced a valuable representation of what could be called good psychiatric formulation. West encourages us to think differently about people and populations with substance use problems, and I now find myself wondering how my clients' epigenetic landscapes might be looking. The work is grounded in common sense and goes a long way towards explaining what the author calls the big observations (‘observation of people in their natural habitat or uncontested scientific evidence’), and it adroitly deals with the challenges inherent in postulating any unified theory of human behaviour. He leaves the way clear for future research and is ready to pass on the baton in the collective endeavour of incremental science.