Consider the range of theories and beliefs that people bring to bear when reasoning about illness. At a minimum, illness can be thought of in biological, social, psychological, moral/religious, and probabilistic terms. Various aspects of illness maybe understood to be embedded in a number of explanatory contexts or theories. Any one “fact” about illness may involve a number of theories. For example there are several (partial) explanations for why sick children do not go to school. There is a biological rationale: sick people may be contagious and so may contaminate others they contact. There is also a social prohibition. It is a social norm that sick people are released from certain obligations and enjoined to others: one gets to stay home and should avoid making others ill. There also may be a psychological rationale: sick people feel bad and weak and so do not want to go to school.

Conceptions of illness provide researchers an excellent opportunity to study children's understandings of different domains of experience. To what extent, for example, do young children distinguish biological from social or psychological aspects of illness experience? This question has taken on particular importance in light of ongoing debates about the development of biological knowledge. Susan Carey and colleagues (Carey, 1985a, 1995; Solomon et al, 1996) have argued that a differentiated notion of biology does not emerge until middle childhood. Other researchers suggest that some forms of biological knowledge are present much earlier (e.g., Simons and Keil, 1995; Wellman and Gelman, 1992).