This chapter examines the dispute between Quine and Carnap about how to understand ontological commitment and what ontology to adopt. The central dispute is over Carnap’s acceptance of abstract objects, including numbers, properties, and propositions, which Quine characterizes in “On What There Is” (1948) as a form of Platonism. Carnap vigorously disagrees, responding in “Empiricism, Semantics, and Ontology” (1950, 1956). For him, commitments to these things are unproblematic consequences of accepting an optimal theoretical framework for doing science. Philosophers haven’t seen this because, he believes, they have approached ontology in an unscientific way.