I got a letter from him written from Monte Cassino, saying that a few days after the Armistice, he had been taken prisoner by the Italians, but fortunately with his manuscript. It appears he had written a book in the trenches, and wished me to read it. He was the kind of man who would never have noticed such small matters as bursting shells when he was thinking about logic. ... It was the book which was subsequently published under the title Tractatus Logico-Philosophicus.