After defining semantical concepts like logical truth and related ones — Rudolf Carnap

"When I met Wittgenstein, I saw that Schlicks warnings were fully justified. But his behavior was not caused by any arrogance. In general, he was of a sympathetic temperament and very kind; but he was hypersensitive and easily irritated. Whatever he said was always interesting and stimulating and the way in which he expressed it was often fascinating. His point of view and his attitude toward people and problems, even theoretical problems, were much more similar to those of a creative artist than to those of a scientist; one might almost say, similar to those of a religious prophet or a seer. When he started to formulate his view on some specific problem, we often felt the internal struggle that occurred in him at that very moment, a struggle by which he tried to penetrate from darkness to light under an intense and painful strain, which was even visible on his most expressive face. When finally, sometimes after a prolonged arduous effort, his answers came forth, his statement stood before us like a newly created piece of art or a divine revelation. Not that he asserted his views dogmatically … But the impression he made on us was as if insight came to him as through divine inspiration, so that we could not help feeling that any sober rational comment of analysis of it would be a profanation."

"Science is a system of statements based on direct experience, and controlled by experimental verification. Verification in science is not, however, of single statements but of the entire system or a sub-system of such statements."

"The task of making more exact a vague or not quite exact concept used in everyday life or in an earlier stage of scientific or logical development, or rather of replacing it by a newly constructed, more exact concept, belongs among the most important tasks of logical analysis and logical construction. We call this the task of explicating, or of giving an explication for the earlier concept; this earlier concept, or sometimes the term used for it, is called the explicandum; and the new concept, or its term, is called an explicatum of the old one."

"A decisive difference between our method and Freges consists in the fact that our concepts, in distinction to Freges, are independent of the context."

"Yes, he is one of my heroes. I took a seminar from him under the GI bill after I got out of the Navy. It was not when I was an undergraduate. That was the only graduate course I ever took. It was on the philosophy of science, and it had a big influence on me. Later, when Carnap was giving the course in California, I persuaded him to have his wife tape record it. She typed it up and sent me the typed version. I edited it into a book called Introduction to the Philosophy of Science. That was the only popular book that Carnap ever did. All I did was edit it into language an average person could understand without knowing any math."

"It was Rudolf Carnap’s dream for the last three decades of his life to show that science proceeds by a formal syntactic method; today no one to my knowledge holds out any hope for that project."