 Carnap’s rejection of ontology, and metaphysics more generally, has been widely criticized from a number of different angles. One common criticism is that it relies on a too simplistic conception of natural language that ties it too closely to science or to evidence and verification. In particular, Carnap’s more general rejection of metaphysics used a verificationist conception of meaning, which is widely seen as too simplistic. Carnap’s rejection of ontology has been criticized most prominently by Quine, and the debate between Carnap and Quine on ontology is a classic in this field. Quine rejected Carnap’s conception that when scientists are faced with data that don’t fit their theory they have two choices. First they could change the theory, but stay in the same framework. Secondly, they could move to a different framework, and formulate a new theory within that framework. These two moves for Carnap are substantially different. Quine would want to see them as fundamentally similar. In particular, Quine rejects the idea that there could be truths which are the trivial internal statements, like “There are numbers”, whose truth is a given once the framework of numbers has been adopted. Thus some such internal statements would be analytic truths, and Quine is well known for thinking that the distinction between analytic and synthetic truths is untenable. Thus Carnap’s distinction between internal and external questions is to be rejected alongside with the rejection of the distinction between analytic and synthetic truths. On the other hand, Quine and Carnap agree that ontology in the traditional philosophical sense is to be rejected. Traditionally ontology has often, but not always, been an armchair, a priori, investigation into the fundamental building blocks of reality. As such it is completely separated from science. Quine rejects this approach to ontology since he holds that there can’t be such an investigation into reality that is completely separate and prior to the rest of inquiry. See his (Quine 1951). See (Yablo 1998) for more on the debate between Quine and Carnap, which contains many references to the relevant passages. The view on ontological commitment discussed in section 4.1., which is usually attributed to Quine, was developed as a reaction to Carnap’s position discussed in this section. Simply put, Quine’s view is that to see what we are committed to we have to see what our best overall theory of the world quantifies over. In particular, we look at our best overall scientific theory of the world, which contains physics and the rest.