The Ronald Knox “Ten Commandments of Detection” (1928)

Bruce Sterling
3 min readAug 29, 2023
Ronald Knox

*Father Knox didn’t create these rules himself, ex cathedra; they came up in group discussions with other early detective-fiction professionals, but he codified and published them.

*I find three aspects of interest here.

*First, these are not technical rules or “tips” about writing effective entertainment fiction. Instead, they’re a social contract among authors and their audience, so that the “detection game” will possess “fair play.” It’s genre as a church culture, with ordained preachers supplying dependable services and keeping the pews filled with edified parishioners. There’s an atmosphere of intentional, conventionalized morality to it; it’s about virtue, faith, trust and justice.

*In a second interesting aspect, Father Knox’s rule-number-four formally removes any science fiction gadgetry. Obviously SF gadget-hacking must be somehow aligned with Detective locked-room hacking: they both scratch the reader’s “howdoneit” itches. They’re intellectual-paraliterary puzzles, as in “What is this, how does it work?” However, contemplating balky, gee-whiz technology and solving subversive crimes are generic rivals. They don’t get along, and so should be segregated.

*Third, in Knox Rule Five, “Chinamen” serve as standins for any or all alien social figures from any novum, fairyland, otherworld or counterculture where the story’s crime might not be clearly and properly judged as crime. Science fiction abounds with “chinamen” characters, but clearly you can’t have a sasquatch, changeling or a saucer-being in any proper detective story; that’s blatantly unfair and even offensive, like a Bible parable where Jesus has a 13th disciple with two heads.

*I’ve never written a detective story; I don’t read a lot of them; after studying this century-old manifesto, I appreciate the craft more, but I’m less tempted to ever try it. I’m grateful for this clearer understanding; another genre’s manifesto is not exclusionary or harsh and does not hurt my feelings; instead, it’s denominational. Colleagues in the detective, mystery or thriller line of work, they don’t need me, and I have little to offer them. They have their own peaked and ivied social centers and their own considered gospel; so let them depart hence in peace.


Ronald Knox, a Catholic priest, in 1928 proposed the following “Ten Commandments of Detection.”

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 follow.

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 upon which he may happen to light.

9. The stupid friend 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.