First published in 1999. This volume is the third of a series devoted to the first years of the child's development, the two others being concerned with the beginnings of intelligence and the child's construction of reality (La naissance de intelligence chez Venfant and La construction du réel chez Venfant). Although this book contains frequent references to the two other volumes, which deal with the same three children and study the relationships between their mental activities, it nevertheless constitutes in itself an independent and complete study