I found the citation, from the introduction to The Caves of Steel. "Campbell had often said that a science-fiction mystery story was a contradiction in terms;

I found the citation, from the introduction to The Caves of Steel. "Campbell had often said that a science-fiction mystery story was a contradiction in terms; that advances in technology could be used to get detectives out of their difficulties unfairly, and that the readers would therefore be cheated. I sat down to write a story that would be a classic mystery and that would not cheat the reader—and yet would be a true science-fiction story. The result was The Caves of Steel. It appeared in Galaxy as a three-part serial in the October, November, and December 1953 issues, and in 1954, it was published by Doubleday as my eleventh book. There was no question but that The Caves of Steel was my most successful book to date. It sold better than any of my earlier books; it elicited nicer letters from readers; and (best proof of all) Doubleday smiled at me with greater warmth than ever before. Until that point, they wanted outlines and chapters from me before handing me contracts, but after that I got my contracts on my mere statement that I was going to write another book."