Talk of “commitment” has an unfortunate connotation: it applies more naturally to persons than to theories. But Quine's criterion should be understood as applying to theories primarily, and to persons derivatively by way of the theories they accept (Quine 1953: 103). It would be more perspicuous to speak simply of the existential implications, or ontological presuppositions, of a theory. But ‘ontological commitment’ is well entrenched, and it would be pointless to try to avoid it.