  Many worlds interpretations (MWI) of quantum mechanics avoid the measurement
problem by considering every term in the quantum superposition as actual. A
seemingly opposed solution is proposed by modal interpretations (MI) which
state that quantum mechanics does not provide an account of what `actually is
the case', but rather deals with what `might be the case', i.e. with
possibilities. In this paper we provide an algebraic framework which allows us
to analyze in depth the modal aspects of MWI. Within our general formal scheme
we also provide a formal comparison between MWI and MI, in particular, we
provide a formal understanding of why --even though both interpretations share
the same formal structure-- MI fall pray of Kochen-Specker (KS) type
contradictions while MWI escape them.
