This paper addresses the variation that the middle construction attests
cross-linguistically. In one class of languges middles behave as passives,
whereas in another class they pattern with unergative structures. My
proposal is that this variation is not accidental, and that it reduces to
variation in the morphosyntax of aspect. I put forward a semantic treatment
of middles as disposition ascriptions to a Patient/Theme argument. I then
show how the morphosyntax of the dispositional generic operator that is
argued to be present in such structures determines the syntactic behaviour
of middles. Genericity may be morphosyntactically encoded by means of
grammatical aspect, in particular in languages where such aspectual
distinctions as perfective/imperfective exist. The proposal is that the level
at which the generic operator is present correlates with the level at which
middles are derived. For instance, in Greek and French, genericity is
morphosyntactically encoded and middles are parasitic on passives. In
such languages, middles are derived in the syntax, in virtue of the availability
in the syntax of the relevant operator. In Germanic languages, by contrast,
aspectual distinctions are not encoded in the morphosyntax, and middles
are syntactically unergative. This is implemented in terms of a presyntactic
derivation.