This paper deals with a series of semantic contrasts between the copula "be" and the preposition "as", two functional elements that both head elementary predication structures. It will be argued that the meaning of "as" is a type lowering device shifting the meaning of its complement NP from generalized quantifier type to property type (where properties are conceived as relations between individuals and situations), while the copula "be" induces a type coercion from (partial) situations to (total) possible worlds. Paired with van der Sandt's 1992 theory of presupposition accommodation, these assumptions will account for the observed contrasts between "as" and "be"
