I should make a distinction between two kinds of readjustment in the case of a conflict with experience, namely, between a change in the language, and a mere change in or addition of, a truth-value ascribed to an indeterminate statement (i.e. a statement whose truth value is not fixed by the rules of language, say by the postulates of logic, mathematics and physics). A change of the first kind constitutes a radical alteration, sometimes a revolution, and it occurs only at certain historically decisive points in the development of science. On the other hand, changes of the second kind occur every minute. A change of the first kind constitutes, strictly speaking, a transition from a language Ln into a new language Ln+1.
Source: "Replies and Systematic Expositions," Schlipp, The Philosophy of Rudolf Carnap [Carnap63], p921
Contributed by: Zaady