A book that presents for the first time the clinical method in detail. Piaget analyses the explanations children give to certain phenomena (such as birth, matter, night, rain and other natural phenomena) as well as the various kinds of indifferentiations specific to children up to the age of 7 (sleep-reality, out-in, moral and physical need, sign and thing, etc.). In this work, child psyche is characterized by realism, artificialism and animism.