1 The reader must have equal opportunity with the detective for solving the mystery. All clues must be plainly stated and described.

      2 No wilful tricks or deceptions may be played on the reader other than those played legitimately by the criminal on the detective himself.

      3 There must be no love interest in the story. To introduce amour is to clutter up a purely intellectual experience with irrelevant sentiment. The business in hand is to bring a criminal to the bar of justice, not to bring a lovelorn couple to the hymeneal altar.

      4 The detective himself, or one of the official investigators, should never turn out to be the culprit. This is bald trickery, on a par with offering some one a bright penny for a five-dollar gold piece. It’s false pretenses.

      5 The culprit must be determined by logical deductions—not by accident or coincidence or unmotivated confession. To solve a criminal problem in this latter fashion is like sending the reader on a deliberate wild-goose chase, and then telling him, after he has failed, that you had the object of his search up your sleeve all the time. Such an author is no better than a practical joker.

      6 The detective novel must have a detective in it; and a detective is not a detective unless he detects. His function is to gather clues that will eventually lead to the person who did the dirty work in the first chapter; and if the detective does not reach his conclusions through an analysis of those clues, he has no more solved his problem than the schoolboy who gets his answer out of the back of the arithmetic.

      7 There simply must be a corpse in a detective novel, and the deader the corpse the better. No lesser crime than murder will suffice. Three hundred pages is far too much pother for a crime other than murder. After all, the reader’s trouble and expenditure of energy must be rewarded. Americans are essentially humane, and therefore a tip-top murder arouses their sense of vengeance and horror. They wish to bring the perpetrator to justice; and when “murder most foul, as in the best it is,” has been committed, the chase is on with all the righteous enthusiasm of which the thrice gentle reader is capable.

      8 The problem of the crime must be solved by strictly naturalistic means. Such methods for learning the truth as slate-writing, ouija-boards, mind-reading, spiritualistic séances, crystal-gazing, and the like, are taboo. A reader has a chance when matching his wits with a rationalistic detective, but if he must compete with the world of spirits and go chasing about the fourth dimension of metaphysics, he is defeated ab initio.

      9 There must be but one detective—that is, but one protagonist of deduction—one deus ex machina. To bring the minds of three or four, or sometimes a gang of detectives to bear on a problem is not only to disperse the interest and break the direct thread of logic, but to take an unfair advantage of the reader, who, at the outset, pits his mind against that of the detective and proceeds to do mental battle. If there is more than one detective the reader doesn’t know who his co-deductor is. It’s like making the reader run a race with a relay team.

      10 The culprit must turn out to be a person who has played a more or less prominent part in the story—that is, a person with whom the reader is familiar and in whom he takes an interest. For a writer to fasten the crime, in the final chapter, on a stranger or person who has played a wholly unimportant part in the tale, is to confess to his inability to match wits with the reader.

      11 Servants—such as butlers, footmen, valets, game-keepers, cooks, and the like—must not be chosen by the author as the culprit. This is begging a noble question. It is a too easy solution. It is unsatisfactory, and makes the reader feel that his time has been wasted. The culprit must be a decidedly worth-while person—one that wouldn’t ordinarily come under suspicion; for if the crime was the sordid work of a menial, the author would have had no business to embalm it in book-form.

      12 There must be but one culprit, no matter how many murders are committed. The culprit may, of course, have a minor helper or co-plotter; but the entire