Consider now Quine's insight, on which the quantifier account is based, that it is bound variables rather than singular terms that carry ontological commitment. To implement this insight, Quine simply eliminated singular terms from the language. But suppose one wanted to be able to apply the quantifier criterion to theories containing singular terms. One could instead switch from standard first-order predicate logic to free logic. In free logics, because one cannot in general derive the existential generalization ‘∃x φ(x)’ from ‘φ(t)’, for singular term ‘t’, singular terms fail to carry ontological commitment. Arguably, then, an inclusive, free logic provides the ideal logical environment for applying the quantifier account.[17]