Quineans have taken the basic expression of ontological commitment to be an assertion of the form '∃ x φ', assimilated to theEnglish 'there is something that is a φ'. Here I take the existential quantifier to be introduced, not as an abbreviation for an expression of English, but via Tarskian semantics. I argue, contrary to the standard view, that Tarskian semantics in fact suggests a quite different picture: one in which quantification is of a substitutional type apparently first proposed by Geach. The ontological burden is borne by constant symbols, and truth is defined separately from reference.