[1] In information systems and artificial intelligence, where an ontology refers to a specific vocabulary and a set of explicit assumptions about the meaning and usage of these words, an ontological commitment is an agreement to use the shared vocabulary in a coherent and consistent manner within a specific context.
(Methods of Logic, 1950, p. 228)Another statement about individuals that appears “ontologically innocent” is the well-known Geach–Kaplan sentence: Some critics admire only one another.
Willard Van Orman Quine provided an early and influential formulation of ontological commitment:[4] If one affirms a statement using a name or other singular term, or an initial phrase of 'existential quantification', like 'There are some so-and-sos', then one must either (1) admit that one is committed to the existence of things answering to the singular term or satisfying the descriptions, or (2) provide a 'paraphrase' of the statement that eschews singular terms and quantification over so-and sos.
[9] Although Quine refers to 'ontological commitment' in this connection,[10] in his rejection of the analytic/synthetic distinction he does not rely upon the formal translation of any particular theory along the lines he has suggested.
In addition, the terms used to interpret the application of the theory are not simply descriptions of sensory input, but are statements in a context.
As Ryan puts it: "Rather than being divided between contingent synthetic claims and indubitable analytic propositions, our beliefs constitute a continuous range from a periphery of sense-reports to interior concepts that are comparatively theory-laden and general.
[15] Ontological parsimony can be defined in various ways, and often is equated to versions of Occam's razor, a "rule of thumb, which obliges us to favor theories or hypotheses that make the fewest unwarranted, or ad hoc, assumptions about the data from which they are derived.
[19] These ideas lead to the following particular formulation of Occam's razor: 'Other things being equal, if T1 is more ontologically parsimonious than T2 then it is rational to prefer T1 to T2.'
Inwagen suggested that Quine's approach provided useful tools for discovering what entities were ontological commitments, but that he had not been successful.
[25] However, this view has been attacked by Jonathan Schaffer, who has argued that truthmaking is not an adequate test for ontological commitment: at best, the search for the truthmakers of our theory will tell us what is "fundamental", but not what our theory is ontologically committed to, and hence will not serve as a good way of deciding what exists.
For example, Jody Azzouni suggests that "There is" does not make any kind of genuine existence-claim when it is used in a sentence such as "There are mice that talk".
Since the meaning of the existential quantifier in formal notation is usually explained in terms of its equivalence to English expressions such as "there is" and "there exist", and since these English expressions are not reliably ontologically committing, it comes to seem that we cannot be sure of our theory's ontological commitments even after it has been regimented into a canonical formulation.