The class-inclusion task: question form and distributive comparisons.

The class-inclusion task is regarded by Piaget as a measure of the child's mastery of the structure of hierarchical classification. Class-inclusion was improved by changing the wording of the question to conform to standard English usage. A theoretical argument is offered that the child's difficulties with this task derive from confusion of collective comparisons, in which properties of classes are compared, and distributive comparisons, in which properties of elements are compared. A grammatical constraint on expression of distributive comparisons--an element of a class cannot be compared to an element of an included subclass--is hypothesized to be overgeneralized to expressions referring to collective comparisons such as the class-inclusion task. This hypothesis accounts for the improvement in class-inclusion performance with changes in wording of the question and for the finding that young children's response to class-inclusion questions and to ungrammatical requests for comparison of an element of a class and an element of an included subclass are similar: the children respond readily but understand wrongly that the comparison involves coordinate classes.