This article attempts to ''situate'' the various versions of constructivist theory by tracing their philosophical origins. Two of the constructivisms, schema and information-processing theory, represent traditional epistemologies and thus, by definition, are modernist in orientation. The remaining four constructivisms adopt a postmodern stance-which is to say they refute the assumptions that knowledge is primarily the property of individuals and that, if it is to have any claim on our allegiance, it must be the product of a foolproof inferential system. Each of these social constructivisms evidences a unique approach to the mind-world dilemma. Each also evidences a unique stance toward the ideal teaching-learning environment.