Back in 1929, Ronald Knox created the Decalogue or Ten Commandments of Detective Fiction, which authors of the Golden Age such as Agatha Christie, Dorothy L. Sayers and Ngaio Marsh largely adhered to. Although many of the rules are logical, some of them seem plain bizarre in 2015. So, are the Ten Commandments of Detective Fiction still relevant today?
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.
This is a rule which has been broken by Queen of Crime Agatha Christie amongst others and frankly it’s not getting the Ten Commandments off to a good start. If handled carefully, this is a device which can work extremely well.
Having an unreliable narrator is not the cop-out many would claim. There are a number of very viable reasons for using the device, including the narrator suffering from severe mental illness such as post-traumatic stress disorder, the narrator using the narration as a device (a nice twist on the concept) or plain obfuscation by the narrator. The latter is the least credible, but again it depends on the narrator’s reasons for doing so.
2. All supernatural or preternatural agencies are ruled out as a matter of course.
I personally lean towards agreeing with this, although I do often like to throw a paranormal aspect into my books (or, rather, my character Ellis Flint does as he’s often tempted by the lazy paranormal explanation when things are seemingly unexplainable).
The issue here is that by allowing the paranormal to be a viable explanation the author runs the risk of straying into deus ex machina territory, which in the world of detective fiction is pure laziness.
3. Not more than one secret room or passage is allowable.
This is a very odd rule. Secret anythings are risky, particularly if they’re held back right until the end when the mystery is revealed. I’m a fan of trickling all the information through to the reader so that when the mystery is revealed they could have quite easily figured it out for themselves — but, of course, I try to ensure that they don’t.
So should there be a limit on secret rooms or passages? No, of course not. Once they’re revealed they’re no longer secret and whilst they’re secret they should fall under the same rules of withholding clues that anything else would.
4. No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end.
The unwieldy scientific explanation is sure to bore the reader, particularly if it means they wouldn’t have been able to work it out for themselves without a PhD in Chemistry. Inventing your own poisons is also a bit of a con as far as I’m concerned, and again strays into deus ex machina territory.
5. No Chinaman must figure in the story.
I’m fairly sure I don’t need to explain why this rule is severely outdated.
6. No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right.
This is another rule I’m unsure of. Accidents can certainly be used, again as long as they don’t stray into deus ex machina territory. An abstract accident (one which doesn’t actually reveal the solution to the detective but instead leads him or her to some form of lateral thinking) is certainly permissible as far as I’m concerned.
As for intuition, Kempston Hardwick is certainly a man of intuition but I never let this stand alone. He might well often have inklings which lead him to investigate a certain area/person/aspect of the crime but this should not be a bad thing. After all, it’s how real detectives work and how real human beings operate.
7. The detective himself must not commit the crime.
This ties in heavily to rule 1 and is effectively built upon the bedrock of the device known as the unreliable narrator. Handled carefully (in the same manner as the general unreliable narrator device), this device is perfectly permissible and has been used to great effect by some of detective fiction’s biggest names.
8. The detective is bound to declare any clues which he may discover.
This is quite vague and ambiguous, but in general I’d tend to agree in terms of not withholding things from the reader (unless there’s a very good reason to do so and it’s handled very carefully. See Gillian Flynn’s Gone Girl for a masterclass in this).
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.
Two quite distinct rules here, I think. Firstly, the sidekick isn’t even necessary but is certainly very handy for a number of reasons (that’s a blog post for another day). In terms of withholding thoughts, I’d refer to rule 8.
With regards to the intelligence of the sidekick, there’s a very good psychological reason for having the detective’s intelligence being higher than average and the sidekick’s slightly lower. But how do you know the intelligence of your reader? Affinity with characters is the most important thing, and a lovable fool (like Ellis Flint) can add wonderful depth as a sidekick.
10. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.
‘Unless we have been duly prepared for them’ is the key here. Simply unveiling the twin/double line at the end without having set up the possibility beforehand strays into deus ex machina territory.
It’s a device I’ve used in one of my books before but the possibility and a big clue was firmly planted early on in the book, meaning that the reader could easily have formed the theory themselves, had they spotted the clue.