Existential bare plurals appear to have a plural meaning in affirmative contexts, but a singular meaning under negation.

(1)

  a. Mary saw zebras. ~> More than one.

  b. Mary didn’t see zebras. ~> Not even one.

I will present a novel theory of this phenomenon. Deviating from the conventional wisdom that competition with the singular indefinite is somehow involved, I argue that the facts can be conceived of in terms of the general trivalence of plural predication (“homogeneity effects”). In particular, both (1a) and (1b) have the third truth value when Mary saw exactly one zebra, just like (2a) and (2b) do when Mary read only some of the books.

(2)

  a. Mary read the books. ~> All of them.

  b. Mary didn’t read the books. ~> None of them.

This approach elegantly accounts for the behaviour of existential plurals using only independently motivated conceptual resources, and overcomes problems that have been raised for the competition-base accounts.