Piaget, Jean (1896–1980), a Swiss psychologist, biologist, and philosopher. Piaget was a pioneer in the field of developmental psychology. He sought to understand the nature and origins of human knowledge by studying the intellectual development of young children. Using experimental methods, he demonstrated that children do not innately understand such concepts as space, time, ethics, or causality, but learn them as they interact with the world around them.

Piaget theorized that children develop logical thinking processes in a regular sequence, revising and correcting their version of reality as they discover new objects or experiences. For example, very young children do not look for an object that has been covered; for them, it has ceased to exist. Only later in their development do they understand that the object has a separate, real existence, even if they cannot see it.

Piaget was born in Neuchâtel, Switzerland. He received a doctorate in biology from the University of Neuchâtel in 1918, and spent most of his career at the University of Geneva (1929–71).

Among Piaget's many books are The Language and Thought of the Child (English translation published 1926); The Origin of Intelligence in the Child (1952); Biology and Knowledge (1971); and The Development of Thought (1977).