ABSTRACT
It is no small thing to sketch the scientific Zeitgeist of a man whose publications cover almost three quarters of a century, who was himself for several years a professor of the history of science, and who wrote with clear sympathy about his father: ‘He did not like hasty judgements and he did not hesitate to defend a polemic when he saw the historical truth deformed.’ 1 I will nevertheless take a chance, which of course, in a short chapter like this, cannot be more than a rough sketch. It might resemble the bizarre lines of the constructivist painters Picasso and Braque, who worked largely in the same period as Piaget but who, remarkably enough, were convinced that they represented the true nature of the visible reality better than the realist painters (an intriguing relationship with the genetic constructivism of Jean Piaget, which I will come back to later in this chapter).
