I think for physical books it's much easier to make money with a copyleft license, so it does weaken the argument for allowing closed source books. I would sti

I think for physical books it's much easier to make money with a copyleft license, so it does weaken the argument for allowing closed source books. I would still personally choose a permissive CC equivalent of a BSD license though (CC BY 3.0), if only because I want other people writing books with permissive CC licenses to be able to incorporate my material. Also, for a closed textbook, a publisher might want to take a couple chapters out of my book, or 10 of the images, and I'm not okay with limiting the amount of quoting.