Rudolf Carnap, a German-born philosopher and naturalized U.S. citizen, was a leading exponent of logical positivism and was one of the major philosophers of the twentieth century. He made significant contributions to philosophy of science, philosophy of language, the theory of probability, inductive logic and modal logic. He rejected metaphysics as meaningless because metaphysical statements cannot be proved or disproved by experience. He asserted that many philosophical problems are indeed pseudo-problems, the outcome of a misuse of language.
Carnap's meaning theory in this book with respect to what kind of it should be adopted is pragmatic as I have expected. But it seems that there is doubtful about the identity between intension and extension ,which he said. Discussing modal matter we must especially be careful about the distinction between de re and de dicto so called rather than intension and extension.