Abstract :
Following Lewis, it is widely held that branching worlds differ in important ways from
diverging worlds. There is, however, a simple and natural semantics under which ordinary
sentences uttered in branching worlds have much the same truth values as they
conventionally have in diverging worlds. Under this semantics, whether branching or
diverging, speakers cannot say in advance which branch or world is theirs. They are uncertain
as to the outcome. This same semantics ensures the truth of utterances typically
made about quantum mechanical contingencies, including statements of uncertainty, if
the Everett interpretation of quantum mechanics is true. The ‘incoherence problem’ of
the Everett interpretation, that it can give no meaning to the notion of uncertainty, is
thereby solved.
