ABSTRACT
In this chapter, the author describes the inclusion problem studied by Albert Morf. The choice of the problem was largely determined by the key position of the inclusion problem in the book by Barbel Inhelder and Jean Piaget with its telling maturational title, The Early Growth of Logic in the Child. In the author's 1963 article in Acta Psychologica, he summarized his understanding of the experimental data and their interpretation in the Piagetian literature regarding the quantification of inclusion relations. The experiments were carried out with 60 5-year-old Amsterdam kindergarten pupils from a part of the city were families lived from lower to middle socioeconomic strata. In their first session the effects of teaching were measured by using both the same sort of materials and the purely verbal questions as used in Group I. The children had to discover the correct solution to the problems themselves.
