"For four and a half months in 1918 I was in prison for pacifist propaganda; but, by the intervention of Arthur Balfour, I was placed in the first division, so that while in prison I was able to read and write as much as I liked, provided I did no pacifist propaganda. I found prison in many ways quite agreeable. I had no engagements, no difficult decisions to make, no fear of callers, no interruptions to my work. I read enormously; I wrote a book, "Introduction to Mathematical Philosophy"... and began the work for "Analysis of Mind". I was rather interested in my fellow prisoners, who seemed to me in no way morally inferior to the rest of the population, though they were on the whole slightly below the usual level of intelligence, as was shown by their having been caught. For anybody not in the first division, especially for a person accustomed to reading and writing, prison is a severe and terrible punishment; but for me, thanks to Arthur Balfour, this was not so."