Ronald Arbuthnott Knox (17 February 1888 – 24 August 1957) was an English priest, theologian and author of detective stories. He was also a writer and a regular broadcaster for BBC Radio. Knox went to Eton College, England, and went on to win several scholarships at Balliol College, Oxford. He was ordained an Anglican priest in 1912 and was appointed chaplain of Trinity College, Oxford, but he left in 1917 upon his conversion to Catholicism. In 1918 he was ordained a Catholic priest.

In addition to being a Catholic priest, theologian, broadcaster, essayist and translator, he also wrote six popular novels in the detective fiction genre. Knox was a student of this particular form of literature and, typical of his astute and powerfully analytical brain, he came up with his own Ten Commandments of Detective Fiction. Here they are:

Okay, this one is rather longwinded but it is logical. If you want your readers to be satisfied at the end, the criminal must be a character they have already met in the course of the book. Using a surprise hobo who has just drifted into town and decided to murder one of the local gentry is cheating. Knox was, of course, aware that this cheat was used in many of the fashionable crime magazines of the day, but found them just as abhorrent as we would do today.

Knox was much more subtle. Yes, the culprit must be a character in the story. But it must not be a character that the reader has had the chance to sympathize with. If the author pulls that trick, the reader feels cheated and is likely never to indulge the writer with any further book purchases. There are exceptions to this rule, nevertheless, as in the case of Agatha Christie’s brilliant “The Murder of Roger Ackroyd,” which was published in 1926. It didn’t hurt her sales one little bit. Evidently, Agatha had a different set of rules…

This is not fantasy we’re dealing with here. It’s real life – well, sort of. Readers are creatures of habit – aren’t we all? – and demand that the author play the game. Here there are no fairies, elves, ghosts, saints, angels, demons or trolls to clutter up the literary landscape. Just give us the facts, right? Except this is fiction and not fact. The novelist Stephen King seems to have done a creditable job of mixing straight fiction with fantasy (as did C.S. Lewis’s pal, Charles Williams). So why is the whodunit exempt? Possibly because, like the hobo in rule 1, it is a device that is too easy and, again, leaves the reader feeling cheated.

Here, Knox sounds peeved about the irritating way in which writers magically produce secret passages in old houses and trick switches in libraries that unlock secret doorways which swing out to allow the protagonist to pass on and discover the secret room. Too many of the thriller writers of the period produced this rabbit out of the hat. The word “secret” is key. Knox wants a straightforward mystery where the reader sees every hand that is played and there are no wild cards. The enjoyment is in guessing the culprit before the detective has revealed who it is, not in wildly surmising architectural anomalies and physical impossibilities.

This, again, would be too easy. Foisting a South-East-Asian weed, or a sinister contraption on the reader smacks of cheating. It is a device that is favored by the writers of adventure stories. John Buchan wasn’t above the odd mechanism or appliance. He used that to give Richard Hannay pause in “The Thirty-Nine Steps” and it didn’t really come off. It was a lazy technique that could have turned out much more convincing if there had been some human interaction, rather than a scene in which the red-faced hero struggles with wooden beams, gears and cogs for half an hour, while the nefarious criminal makes his escape.

Chinaman? What Chinaman? This harks back to the dying days of the British Empire when all sorts of foreign nationals were flooding into London to do commerce with the biggest power players on the planet. The Chinaman was regularly used as the evil mastermind character in the magazines of the day. In the 1920s the Chinese were seen as exotic, sinister and somehow not quite above board. Here they were infiltrating British society, selling their unfamiliar wares and slightly distasteful take on life to the masses in the great metropolis. They were trying to take over our lives, by Jove!

When you pick up any appliance, from a toothbrush to a garden hose, and find the words: “Made in China,” you have to ask yourself if things have changed significantly in a hundred years – including our attitudes.

The premise of all classic whodunits is that the reader must be presented with all the same facts that the detective has. The purpose of this is to give the reader an equal chance to solve the puzzle. Coincidences, chance happenings and bizarre hunches rob the reader of that sense of being just as smart as the hero of the piece, because they are the hand of external agency in a world we thought was a level playing field. Readers are sensitive to that in the same way that cryptic-crossword solvers are sensitive to being given a fair chance to complete the puzzle by being given fair clues.

In reality there is little room for this particular brand of shenanigan. Many detective novels are designed to be part of a series in which the detective solves crime after crime. If the culprit turns out to be the same person who is investigating, then the author has effectively shot him- or herself in the foot in terms of a putative sequel. It is true that the most convincing detective characters should also have their own faults and wrestle with their own demons. But the author must stop short of allocating blame for the main crime to the detective, otherwise what you end up with is a kind of moral anarchy in which the reader ceases to care about solving the crime.

This is a tricky one. As mentioned, the reader should have the same chance to solve the crime that the detective has. But to the same extent the author must have enough latitude that he or she does not have to telegraph each clue. Often the best way to introduce clues is as asides, or in minor conversations, or in apparently insignificant details arising that are quickly passed over. In that case, the reader really does know each clue, but not its immediate significance for the solving of the crime.

The Watson character’s purpose is to highlight the intelligence of the detective, ask the same questions that the reader is asking, and occasionally to summarize the investigation’s progress so far. The reason why he has to be dumber than the reader is to give the reader that superb sense of superiority that comes from being one step ahead of him. In a sense, the reader should be able to answer many of the questions that the Watson figure articulates.

These literary devices, by our time, have worn decidedly thin and smack of the lazy author who can’t resist pulling a fast one in order to solve chunks of the puzzle. Even if the author has prepared the reader for the appearance of the twin or double, the modern reader will experience a sense of letdown when the fact is revealed.

Virtually all of these “rules” have been broken by successful novelists who had the skill to hold the reader’s attention beyond the first few pages, through the ensuing story, right to the denouement. In fact, many of Knox’s rules seem superfluous, or at least partially inapplicable to modern day detective fiction. And yet, taken as a whole, they present us with the proposition that, in this particular genre, care must be taken over the telling, the explication and the execution of a story that is meant to be an entertainment which challenges the reader’s intellect and is worth the price on the cover of the book.