> Remarkably, Wittgenstein was in occasional correspondence with English friends throughout the war. He records letters from Russell, John Maynard Keynes, and especially David Pinsent, a Cambridge contemporary whom he loved and thought of constantly.

That does seem almost shocking. How does that even work? I would have thought that if an active service military personnel tried to mail something from the front to an enemy country, it would surely be intercepted and thoroughly examined and/or stopped. Would each side send letters through some mutual acquaintance in some neutral country? Did the Austo-Hungarians not have censors on military communication? Did the already alienated author of so many numbered cryptic statements ever fear he would be investigated as a spy?