Van Dine S.S. Twenty rules for writing detective stories

(Originally published in the American Magazine (1928-sep), and included in the Philo Vance
investigates omnibus (1936)
THE DETECTIVE story is a kind of intellectual game. It is more — it is a sporting event.
And for the writing of detective stories there are very definite laws — unwritten,
perhaps, but none the less binding; and every respectable and self-respecting
concocter of literary mysteries lives up to them. Herewith, then, is a sort Credo,
based partly on the practice of all the great writers of detective stories, and partly on
the promptings of the honest author's inner conscience.