The technical apparatus of modal semantics--Possible worlds, World-Lines, Counterparts, Etc.--Continues to arouse suspicion among philosophers of various persuasions. A way to dispel at least some of the suspicion is to provide a naturalistic interpretation of the semantical machinery. My goal here is precisely that. More specifically, I provide a behavioristically acceptable interpretation of david lewis' counterpart theory. Reference to worlds and counterparts is construed in sober, Quinean terms. The result is a "metalinguistic" construal of counterpart semantics, And thus, Of modality. (...) Having shown that counterpart theory rests on no dubious philosophical assumptions, I briefly explore some of the metaphysical consequences of the resulting theory of modality. (shrink)