Carnap's theory of linguistic frameworks (and the distinction between internal and external questions which comes with it) is in many ways an appealing approach to philosophy. It offers us a way of explaining the special a priori status of mathematics and logic; it allows us to dismiss a great many metaphysical questions as pseudo-questions; and, unlike the Kantian picture, it can accommodate the radical changes in our ideas of space, time and causation that took place in the twentieth century.

We need to grasp this Carnapian picture if we are to understand the most prominent naturalist philosopher of the twentieth century: Willard van Orman Quine. Quine's naturalism emerges from his criticism of Carnap's philosophy. In particular, as we shall see, Quine raises serious questions about the different ways internal and external questions are supposedly settled according to Carnap.

Recall that, according to Carnap, within a framework an internal question (if it is empirical) is settled by appeal to empirical evidence; external questions, such as whether to adopt the thing-language, are settled by pragmatic considerations of simplicity, fruitfulness of the framework, etc.

Let us think about a piece of science conducted within the thing-language. Suppose I have some astronomical theory that predicts the motions of the planets. Let us say I am a nineteenth-century astronomer testing Newton's theory of gravitation. Newton's theory all by itself does not predict anything. I need to combine it with other claims.