If Kirkpatrick taught Lewis to think critically—to demand evidence for even the most casual assertions—Oxford introduced him to a wide horizon of ideas. Whereas Lewis’s hard-pressing mentor had helped him reinforce his atheism, a few associates at Oxford forced him to re-examine his belief in a universe without God. The pond up the hill from the Kilns, in which Lewis and J.R.R. Tolkien used to swim, and Lewis’s stepson, Douglas, sank a boat.