Family therapists are being exhorted to adopt a social constructionist epistemology and to abandon science as a valid form of knowing. Epistemological objections to science are usually directed at ‘positivism’, an outmoded view that is largely discredited among practising scientists. Contemporary science, is rather, constructionist, differing from other constuctionist approaches only in ways of arbitrating between world views. Criticisms aimed at science apply to all forms of discourse, including family therapy. I conclude that science has failed family therapy at the practical, not the philosophical level.