In 1928, the following list of 20 Rules appeared in the September edition of The American Magazine. They were written by author S S Van Dine (1888-1939) - real name Willard Huntington Wright) - whose wealthy amateur sleuth Philo Vance remains one of the most pompous, pretentious, insufferable detectives in fiction (Some of Van Dine's contemporaries noted that the character was not unlike the author). However, he was hugely popular.
So here are the rules (I have removed some of the finer detail to reduce reading time. If you want to see the full thing, click here).
Twenty Rules for Writing Detective Stories
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.
4. The detective himself, or one of the official investigators, should never turn out to be the culprit.
5. The culprit must be determined by logical deductions - not by accident or coincidence or unmotivated confession.
6. The detective novel must have a detective in it; and a detective is not a detective unless he detects.
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.
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 seances, crystal-gazing, and the like, are taboo.
9. There must be but one detective - that is, but one protagonist of deduction - one deus ex machine.
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.
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.
12. There must be but one culprit, no matter how many murders are committed.
13. Secret societies, camorras, mafias, et al., have no place in a detective story.
14. The method of murder, and the means of detecting it, must be rational and scientific. That is to say, pseudo-science and purely imaginative and speculative devices are not to be tolerated in the roman policier.
15. The truth of the problem must at all times be apparent - provided the reader is shrewd enough to see it.
16. A detective novel should contain no long descriptive passages, no literary dallying with side-issues, no subtly worked-out character analyses, no "atmospheric" preoccupations. Such matters have no vital place in a record of crime and deduction.
17. A professional criminal must never be shouldered with the guilt of a crime in a detective story. Crimes by house-breakers and bandits are the province of the police department - not of authors and brilliant amateur detectives.
18. A crime in a detective story must never turn out to be an accident or a suicide.
19. The motives for all crimes in detective stories should be personal. International plottings and war politics belong in a different category of fiction.
20. And (to give my Credo an even score of items) I herewith list a few of the devices which no self-respecting detective-story writer will now avail himself of:
- Determining the identity of the culprit by comparing the butt of a cigarette left at the scene of the crime with the brand smoked by a suspect.
- The bogus spiritualistic seance to frighten the culprit into giving himself away.
- Forged finger-prints.
- The dummy-figure alibi.
- The dog that does not bark and thereby reveals the fact that the intruder is familiar.
- The final pinning of the crime on a twin, or a relative who looks exactly like the suspect.
- The hypodermic syringe and the knockout drops.
- The commission of the murder in a locked room after the police have actually broken in.
- The word-association test for guilt.
- The cipher, or code letter, which is eventually unravelled by the sleuth.
Okay, have you got all that? Good.
Then, in 1929, the British author and theologian Ronald Knox also made an attempt to create his own (mercifully) shorter Ten Commandments for Detective Fiction. They are that:
1. The criminal must be mentioned in the early part of the story but must not be anyone whose thoughts the reader has been allowed to know.
2. All supernatural or preternatural agencies are ruled out as a matter of course.
3. Not more than one secret room or passage is allowable.
4. No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
5. No Chinaman must figure in the story.
6. No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.
7. The detective himself must not commit the crime.
8. The detective is bound to declare any clues which he may discover.
9. The ‘sidekick’ of the detective - the ‘Watson’ - must not conceal from the reader any thoughts which pass through his mind: his intelligence must be slightly, but very slightly, below that of the average reader.
10. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.
I can think of murder-mysteries that break all 30 rules. And I broke a few myself with my book. But rules are made to be broken ... aren't they?