Participants in the debate about `ontological commitment' would benefit from distinguishing two different ways of understanding the notion. If the question at issue is `what is said to be' by a theory or `what a theory says there is', we are debating `explicit' commitment, while if we ask about the ontological costs or preconditions of the truth of a theory, we enquire into `implicit' commitment. I defend a conception of ontological commitment as implicit commitment; I also develop and defend an account of existentially quantified idioms in natural language which sees them as implicitly, but not explicitly, committing. Finally, I use the distinction between two kinds of ontological commitment to diagnose a flaw in a widely-used argument to the effect that existential quantification is not ontologically committing.
The question of ontological commitment is the question of `what a theory says there is'. 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 the theory of ontological commitment remains in poor shape, and we lack consensus even with regard to the most basic questions: how should we give precise formulation to the notion of ontological commitment, and should we treat existentially quantified idioms as ontologically committing? Without agreement on foundational issues such as these, ontology is an impossible discipline, for unless we understand which sentences in the language of our theory may be used in ways which are ontologically committing, we cannot know whether theories put forward by would-be ontologists have the ontological significance they want them to have. Indeed, some would argue that the absence of agreement about ontological commitment shows that ontology is an impossible discipline. See for example H-J. Glock, `Does Ontology Exist?', Philosophy 77 (2002), pp.235-260. I take it that the establishment of a working theory of ontological commitment is a crucial prolegomenon for any metaphysician who believes that ontological debate is possible and desirable.
In this paper, I suggest answers to the two questions raised above. With regard to formulating the notion of ontological commitment itself, I distinguish two different ways of understanding the notion; once the distinction is made, it becomes apparent that only one of these conceptions of ontological commitment yields a theory of commitment that is of interest to the serious ontologist. With regard to the ontological commitment of existentially quantified idioms, I suggest that such idioms are committing in only one of the two senses I distinguish. Further, I claim that the distinction between two ways of understanding ontological commitment shows why a commonly-used argument against treating existential quantification as committing has no force.
*`Explicit' and `Implicit' Ontological Commitment
At first glance,...