Editing Ontological commitment (section)

===Ontological parsimony===
Whatever process one uses to determine the ontological commitments of a theory, that does not prescribe what ontological commitments one should have. Quine regarded this as a matter of [[epistemology]], which theory one should accept. "Appeal is made to [concerns of] explanatory power, parsimony, conservatism, precision, and so on".<ref name=Routledge/>

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."<ref name=Henke/> Glock regards 'ontological parsimony' as one of the 'five main points' of Quine's conception of ontology.<ref name=Glock/>

Following Quine,<ref name=QuineW/> Baker states that a theory, ''T'', is ''ontologically committed'' to items ''F'' if and only if ''T'' entails that ''F′''s exist.  If two theories, ''T<sub>1</sub>'' and ''T<sub>2</sub>'', have the same ontological commitments except that ''T<sub>2</sub>'' is ontologically committed to ''F′''s while ''T<sub>1</sub>'' is not, then ''T<sub>1</sub>'' is more parsimonious than ''T<sub>2</sub>''. More generally, a sufficient condition for ''T<sub>1</sub>'' being more parsimonious than ''T<sub>2</sub>'' is for the ontological commitments of ''T<sub>1</sub>'' to be a proper subset of those of ''T<sub>2</sub>''.<ref name=Baker/>

These ideas lead to the following particular formulation of Occam's razor: 'Other things being equal, if ''T<sub>1</sub>'' is more ontologically parsimonious than ''T<sub>2</sub>'' then it is rational to prefer ''T<sub>1</sub>'' to ''T<sub>2</sub>''.'  While a common formulation stipulates only that entities should not be multiplied beyond necessity, this version by contrast, states that entities should not be multiplied ''other things being equal'', and this is compatible with parsimony being a comparatively weak theoretical virtue.<ref name=Baker/>