Jean Piaget (9 August 1896 – 16 September 1980) was a Swiss developmental psychologist. He developed a programme of research he called 'genetic epistemology' which explored cognitive development. He produces a model of four main stages (with various subdivisions) of cogntiive development that all nornally developing humans follow. The fouth level, formal operations (seen as critical for abstract thinking about scientific concepts) usually only developed during adolescence. This theory has been very influential.
Piaget saw himself as a kind of naturlist, but studying organims that were human! He favoured a naturalistic approach to his research, but developed the clinical interview method as a compromise between observation and collecting data about children's thinking at a viable rate. His works include many examples of children's thinking (including animism, magical thinking, egocentric thinking…).
