Lewis has argued that impossible worlds are nonsense: if there were
such worlds, one would have to distinguish between the truths about their
contradictory goings-on and contradictory falsehoods about them; and
this--Lewis argues--is preposterous. In this paper I examine a way of
resisting this argument by giving up the assumption that `in so-and-so world'
is a restricting modifier which passes through the truth-functional
connectives. The outcome is a sort of subvaluational semantics which makes
a contradiction 'A and not-A' false even when both 'A' and 'not-A' are true, just as supervaluational semantics makes a tautology 'A and not-A'
true even when neither 'A' and 'not-A' are.