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.
This book was something I wanted to read for two reasons. First, I've read a modest amount of Popper, and he was a big admirer of Carnap; second, I'm fairly sure I got directed to this book via Fr. Spitzer's book New Proofs for the Existence of God somehow. Once I tackled it, it became my own inadvertent introduction to symbolic logic. It will be interesting at some point to attack the subject again and see how the logical and semantic machinery of "language systems" has evolved and been adapted in the decades since.
As for the actual content of the book, Carnap sets up a necessarily tightly controlled complex of ideas about "language systems" and then lays out at great length, via steps that are really pretty simple even when the symbols get quite dense, a theory of inductive relationships that incorporates and extends the concepts of deductive logic. I certainly concentrated more on the text than on the symbols or, for that matter, the usually quite elementary examples. Toward the end you see his system start to produce the mathematical results you would expect to see in a probability & stats textbook. I'm satisfied with my level of comprehension of what he did, but I would hardly call myself qualified to judge whether he was successful. I certainly rarely if at all thought he went out on a limb and made unreasonable assumptions or jumps in logic that weren't explainable due to my unfamiliarity with the symbols, which are not the same ones that get used in modern programming or scripting and which I became only partly conversant with.