1. in the philosophy of science, the position that theories are not to be considered as either true or false but as instruments of explanation that allow observations of the world to be meaningfully ordered. This view is related to Machian positivism.

2. a theory of knowledge that emphasizes the pragmatic value, rather than the truth value, of ideas. In this view, the value of an idea, concept, or judgment lies in its ability to explain, predict, and control one’s concrete functional interactions with the experienced world. This view is related to pragmatism. [developed by John Dewey]

3. the view or attitude that the primary motivation for social interaction is the attainment of some positive advantage or good for the self, so that others are regarded and used as instruments in acquiring such advantage. —instrumentalist adj., n.