What appears to be true in one person's eyes may not be so in another's. When you tell a lie you know what you are doing, but when you are told a lie you do not necessarily recognise it as such. Why is the ability to tell the truth a uniquely human trait? What is the relationship between events or objects in the external world and the objects of our thoughts or the inner states produced by our brains? What makes the relationship between the inner and outer worlds possible? How does it come about? How is it put to the test? How does it evolve? How can we validate the equivalence between what we know of the world and its reality — except by communicating with language and by submitting our knowledge to critical discussion? Isn't this the very origin of science?

These are some of the questions that Jean-Pierre Changeux examines from a new angle, in the light of recent scientific research on the brain.

Following L'Homme neuronal, this is another major work by Jean-Pierre Changeux.

Jean-Pierre Changeux, a neurobiologist, is an honorary professor at the Collège de France and at the Institut Pasteur. He is a member of the French Academy of Sciences and the author of L'Homme artificiel (2007) and Raison et plaisir (1994), and the co-author of La Nature et la Règle (with Paul Ricœur, 1998) and Matière à pensée (with Alain Connes, 1989).