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The Rules of the Game

In the 1920s, Ronald Knox, Sherlock Holmes enthusiast and himself author of several detective stories, was engaged in trying to codify the ground rules of detective stories. Like others of his generation, he saw the genre as a kind of game – ‘a mystery whose elements are clearly presented to the reader at an early stage in the proceedings, and whose nature is such as to arouse curiosity, a curiosity which is gratified at the end.’

The ‘Ten Commandments of Detection’, laid down by Ronald Knox in 1928:

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.

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It was by no means the case that all earlier detective fiction had obeyed the rules formulated by Knox, and it was easy to find violations amongst writers of the time. But writers of detective stories during the ‘Golden Age’ would generally have agreed with the basic intentions behind these ‘Commandments’ – that is, would have agreed that what they were doing was creating ingenious puzzles and presenting them in ways that would keep readers guessing until the final elucidation of the crime. Later definitions of the classic detective story have not simply been based, of course, on the rules set out by Knox, but they have always taken account of the rule-bound and convention-bound nature of the genre. Julian Symons, for example, in Bloody Murder, includes in his definition of the detective story the following:

Plot. Based on a deception which may be mechanical (locked room), verbal (misleading remarks), concerned with forensic medicine…or ballistics. Book is constructed backwards from this deception, revelation of which is the climactic point…

Detective. May be professional or amateur…Always at the centre of the story’s action, most often the hero, and generally a keen observer who notices things missed by others.

Method. If the crime is a murder (it almost always is), method may be bizarre or misleading…Sometimes method may be highly ingenious, as in a locked room mystery, or itself puzzling…

Clues. An essential element. There will be perhaps a dozen of them in the story. The detective may explain their meaning at the time, or deductions may be left to the reader.

Characters. Only the detective is characterized in detail. Otherwise characterization is perfunctory, particularly after the crime when people become wholly subsidiary to the plot.

Setting. Mostly confined to what happened before the crime. Later plot and clue requirements take over and setting…fades.

Social attitude. Conservative.

Puzzle value. Generally high. The detective and the puzzle are the only things that stay in the memory.