 In … cases [of reduction in which the vocabularies of the two relata of the reduction relation differ], the distinctive traits that are the subject matter of the [reduced] science fall into the province of a theory that may have been initially designed for handling qualitatively different materials…. The [reducing] science thus seems to wipe out familiar distinctions as spurious, and appears to maintain that what are prima facie indisputably different traits of things are really identical. (Nagel 1961: 340)