Conceptions of psychological causality refer to the child's grasp of the other's motives and intentions as causes of behavior. The problems studied were (a) age differences in grasp of psychological causality during middle childhood, (b) the exploration of possible mediating abilities of a physicallogical nature accounting for such age differences and (c) relations between cognition of psychological causality and intentionality in moral judgment. The Ss were 175 children (88 boys, 87 girls), aged 6-12. Age and measures derived from conservation and verbal conceptualization items showed independent relations (all atp < .01) to a Motivation Index derived from responses to stories representing rudimentary analogues of defense mechanisms. The Motivation Index was also related to greater use of intentionality in moral judgment (p < .01). Girls scored significantly higher on the Motivation Index (p < .05). Higher motivation scores were obtained by higher scholastic achievers (p < .01). The results were discussed both in terms of cognitive processes common to the motivational and physical-logical test content and in terms of some degree of independence between these two types of cognitive content.There has been a marked research emphasis on the child's conceptions of physical causality (e.g., 3, 11, 15,19,20). By contrast there has been a more limited focus on the child's grasp of psychological causality: i.e., his interpretation of others' motives and intentions as causes of behavior [but see (1,4, 7, 8,25, 26)].The above consideration has stimulated the exploration of several problems.1. There is first a developmental problem. A question is whether performance differences in grasp of psychological causality arise in the ages between six and 1 1. During this age interval, according to Piaget (22), the child emerges from the preoperational period, moves into the concrete operational stage, and begins the formal operational stage. Are such profound developments in the grasp of physical reality accompanied by growth in the cognition of motive?2. There is a mediational problem. Aside from the raw association between age and performance on conceptions of psychological causality, are there mediating abilities of a relatively general nature which may account for the relations? Research bearing on such a mediational function might focus on (a) whether these abilities relate to motivational perception independently of age, and (b) whether control on such abilities renders nonsignificant the relation between age and motivational perception. Two kinds of ability might be candidates for such a mediational role.The first is conservation achievement, which relates to a concrete operational mode of thought. The latter for Piaget renders possible the child's grasp of the dispositional quality of the physical world: e.g., its conserved properties of mass and quantity. Would evidence of operational thought, as reflected in conservation performance, help to account for the developing child's grasp of psychological dispositions (e.g., th...