When scientists or the everyday Joe ask whether quarks exist, they are asking what Carnap calls an internal question . When philosophers ask whether quarks exist, they are generally asking what Carnap refers to as an external question . Internal and external questions, although phrased in exactly the same way, turn out to be very different questions. A new framework is presumably built whenever one wishes to talk about a new type of entity. Internal questions are questions that ask whether something exists within a given framework.
External questions are questions about the existence of the entire type of entities.
As Carnap says, internal questions are to be answered by empirical investigations. To recognize something as a real thing or event means to succeed in incorporating it into the system of things at a particular space-time position so that it fits together with the other things recognized as real, according to the rules of the framework. In other words, to accept quarks as real means to be able to fit them into the list of things that pass the tests within one's lingustic framework. The acceptance of quarks as real does not entail that the person believes that there is a world of real things - it simply means that he is committed to a certain way of speaking, and that that way of speaking happens to commit him to affirming that quarks exist. Philosophers, Carnap believes, like to ask entirely different questions - they like to ask about the metaphysical reality of entire types of things.