  If some version of underdetermination were true, how should we respond? This is an issue on which Quine has not merely changed his mind but vacillated, going back and forth between what he calls the “sectarian” and the “ecumenical” responses. The sectarian response is to say that we should not let the existence of the alternative in any way affect our attitude towards our own theory: we should continue to take it seriously, as uniquely telling us the truth about the world. (We are assuming that the two theories possess all theoretical virtues to equal degree; clearly Quine would say that if one theory were superior in some way then we would have reason to adopt it.) The ecumenical response, by contrast, counts both theories as true. In almost his last word on the subject he suggests that there may be little at stake since the “fantasy of irresolubly rival systems of the world” takes us “out beyond where linguistic usage has been crystallized by use” (1990a, 100f).