Evaluates empirical studies on child development. Suggests that most such research consists of studies of a priori, nonempirical, logical relations between concepts, whose definitions guarantee the relationship studied. Argues that hypotheses are empirical if variables involved are semantically and logically independent. Research that is not based…

The pattern of parent-child correlations in adoption studies has long been interpreted to suggest substantial additive genetic variance underlying variance in IQ. The studies have frequently been criticized on methodological grounds, but those criticisms have not reflected recent perspectives in genetics and developmental theory. Here we apply…

Comments on the ideas espoused by Smedslund (PS 522 552) in this issue. Agrees to the idea of spending more intellectual energy in distinguishing between a priori and empirical hypotheses but emphasizes that concepts are not always accurate reflections of reality and that even empirical disconfirmation of an a priori hypothesis sometimes can…