Simplexity is the set of solutions that living organisms find so that despite complex natural processes the brain can prepare actions and project their consequences. These solutions are principles of simplification that enable an organism to deal with information and situations, while taking into account past experiences and anticipating future ones. Such solutions are not caricatures, shortcuts or summaries; they are instead new ways of addressing problems so that actions may be taken more quickly, more elegantly and more efficiently.

In a sense, the history of living organisms may be summed up by their remarkable ability to find solutions that avoid the world's complexity by imposing on it their own rules and functions. Thus the notions of simplexity and simplicity differ fundamentally: the former includes tension, a relationship and sometimes opposition between simplicity and complexity.

In other words, in a complex world, solutions are not simple because there can be no simple solutions — they are necessarily “simplex”.

Evolution has resolved the problem of complexity not by simplifying but by finding solutions whose processes — though they can sometimes be complex — allow us to act in the midst of complexity and of uncertainty. Nature can inspire us by making us realise that simplification is never simple and requires instead that we inhibit, select, relate and imagine, in order to act in the best possible manner.

This book introduces a new concept: simplexity, which may be defined as the means by which the brain prepares actions and anticipates consequences, despite the complexity of natural processes. Simplexity is a biological theory with many concrete applications: it shows how evolution has resolved the problems of complexity not through simplification but by favouring solutions — sometimes complex ones — that facilitate action.

Alain Berthoz is a professor at the Collège de France where he heads the Laboratory of Physiology, Perception and Action. He is the author of Le Sens du mouvement (1997) and La Décision (2003).