French psychologist, philosopher, and naturalist.

Jean Piaget is universally known for his studies of the development of intelligence in children. Although he is one of the creators of child psychology as it exists today, psychology was for him only a tool of epistemology (the theory of knowledge). He identified his domain as "genetic [i.e., developmental] epistemology." He thus studied the growth of children's capacity to think in abstract, logical terms, and of such categories as time, space, number, causality, and permanency, describing an invariable sequence of stages from birth through adolescence. A prolific author, he wrote over fifty books and hundreds of articles.

Piaget was born in 1896 in the French-speaking Swiss city of Neuchâtel, the son of an agnostic medievalist and a religious mother with socialist leanings. After completing a doctoral thesis in natural sciences (1918), and studies in psychology and philosophy in...