Incommensurability in cognitive guise

Philosophers and historians of science have made the claim that successive scientific theories are incommensurable, that is, that many or all of their concepts fail to coincide. This claim has been echoed by cognitive psychologists who have applied it to the successive conceptual schemes of young children, or of children and adults. This paper examines the psychological evidence for the claim and proposes ways of reinterpreting it which do not involve imputing incommensurability. An alternative approach to understanding conceptual change is suggested, according to which novel concepts are introduced against a background of shared concepts, rather than as part of incommensurable conceptual schemes.