”10 commandments of Detective Fiction”
by Ronald Knox
Ronald Knox was an English Catholic priest and mystery fiction writer in the early 20th century. He belonged to the Detection Club, a society comprised of notable mystery writers like Agatha Christie, Dorothy Sayers (Lord Peter Wimsey), G. K. Chesterson (Father Brown), and E. C. Bentley. His novels include: The Viaduct Murder, Double Cross Purposes, Still Dead.
- The criminal must be someone mentioned in the early part of the story, but must not be anyone whose thoughts the reader has been allowed to follow.
- All supernatural or preternatural agencies are ruled out as a matter of course.
- Not more than one secret room or passage is allowable.
- No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
- No Chinaman must figure in the story.
- No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.
- The detective must not himself commit the crime.
- The detective must not light on any clues which are not instantly produced for the inspection of the reader.
- The stupid friend of the detective, the Watson, must not conceal any thoughts which pass through his mind; his intelligence must be slightly, but very slightly, below that of the average reader.
- Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.
*originally published in 1924 – reprinted with commentary in Literary Distractions in a chapter titled “Detective Stories” (180-198). In this chapter, Knox cites Christie for violating #1 and Conan Doyle for violating #4 & #8. It omits #10 all together (outlining only 9 rules).