Participants in the debate on “ontological commitment” would benefit from distinguishing two different ways of understanding the notion. If the question at hand is "what a theory says" or "what a theory says exists", we are debating "explicit" commitment, whereas if we are asking about ontological costs or conditions prerequisites of the truth of a theory, we investigate the “implicit” commitment. I defend a conception of ontological commitment as implicit commitment; I also develop and defend a view of existentially quantified idioms in natural language that sees them as implicitly, but not explicitly, engaging. Finally, I use the distinction between two types of ontological commitment to diagnose a flaw in a widely used argument that existential quantification is not ontologically engaging. The question of ontological commitment is the question of “what a theory says exists.” . So much is familiar to any student of Quine. See Quine, “On What There Is,” repr. in his From a Logical Point of View (Cambridge: Harvard University Press, 1980), pp.1-19, especially p.15ff. Yet ontological commitment theory remains in poor shape, and we lack consensus on even the most fundamental questions: how should we precisely formulate the notion of ontological commitment, and should we treat idioms existentially? quantified as ontologically engaging? Without agreement on fundamental questions like these, ontology is an impossible discipline, because unless we understand which phrases of the language of our theory can be used in a way that is ontologically engaging, we cannot know whether the Theories put forward by potential ontologists have the ontological meaning they wish to give them. Indeed...... middle of paper ...... in all sentences which make ontological assertions about s but say of certain named objects that they are s. On some not unreasonable views of situational semantics, specifically, that sentences containing nouns are not disguised existential quantifications, and that there can be no truth expressed by a sentence of the form "a is a” where the noun a fails to refer. The theory cannot be true unless there are s, yet the theory contains no sentence like “There are s” that could count as an ontological claim about s. Although s is not one of the theory's explicit commitments, it is certainly true that the theory is committed to s in some sense, because if the theory is true then s must exist, and anyone who endorses the theory but does not believe not that Existence deserves to be criticized for not recognizing the ontological cost of its theory..