Ad Hoc is 'For the purpose of...'

Three days had passed, and California's contribution to the Charles' tradition had not tampered with the Clock Tower's contents. He had found a Douay bible, and a Gideon's. The Gideon's was a donation from his corporate sponsor, and he treasured it. All he had to do to quote Latin NOW, was to look up the phrase he wanted in Gideon's and cite the self-same passage in the Douay. If he got caught, he had a plan: Put the Douay Translation right back in the library, but not where he had found it. He would put it in the History section. The only one who could POSSIBLY give him away was Dewey!