  In order to threaten realism, a version of underdetermination would thus have to assert that our postulated complete global theory of the world has empirically equivalent alternatives and that no translation from one theory to the other is possible. Since the predicates of the theory are its only non-logical vocabulary, this is equivalent to saying that we cannot obtain one from the other by reconstruing the predicates of the theory. Quine comments: “This, for me, is an open question.” (1975a, 327). Much of his subsequent discussion of underdetermination takes place in terms of the weaker idea that our theory might have empirically equivalent alternatives and that “we would see no way of reconciling [them] by reconstrual of predicates” (loc. cit, emphasis added; cf. also 1990a, 97).