Abstract
The question of how concepts are formed was central for positivist and operationalist philosophers concerned to root scientific thought directly in experience. Although the positivist program has been abandoned, the current interest in the philosophy of scientific discovery shows the need for a theory of conceptual development. This paper offers a theory of how new concepts can arise, not by abstraction from experience or by definition, but by conceptual combination. Such combination produces a new concept as a non-linear, non-definitional amalgam of existing concepts. After proposing rules intended to account for a variety of mundane cases of conceptual combination, the paper presents several illustrations of how scientific concepts have arisen through combination.