Although originally published in France in 1951 this English translation was not published until 1975. The book supplements the authors’ previous publications on the development of thought in the child and is the result of two preoccupations: how thought that is in the process of formation acts to assimilate those aspects of experience that cannot be assimilated deductively – for example, the randomly mixed; and the necessity of discovering how the mental processes work in the totality of spontaneous and experimental searchings that make up what is called the problem of ‘induction’. Induction is a sifting of our experiences to determine what depends on regularity, what on law, and what on chance. The authors examine the formation of the physical aspects of the notion of chance; they study groups of random subjects and of ‘special’ subjects; and they analyse the development of combining operations which contributes to determining the relationship between chance, probability, and the operating mechanisms of the mind.