The Ten Commandments of Detective Fiction

Roman Catholic Monsignor lays down the ‘fair play’ rules for crime writers

Ronald Knox was a priest as
well as a crime writer

Ronald Knox, the crime writer most remembered for writing the Ten Commandments of Detective Fiction, was born on this day - 17 February - in 1888 in the village of Kibworth Harcourt in Leicestershire.

Knox became a Roman Catholic priest and produced the Knox Bible, translating the Latin Vulgate bible into English using Hebrew and Greek sources. He was also a theologian, satirical writer and radio broadcaster.

The son of a Church of England clergyman who became a bishop, Knox was educated at Eton and Balliol College, Oxford.

He was ordained an Anglican priest and appointed chaplain of Trinity College, Oxford. During World War 1 he served in military intelligence.

When Knox converted to Roman Catholicism, his father cut him out of his will. Knox explained his conversion, which was partly influenced by the crime writer G K Chesterton, by writing two books about it. When G K Chesterton also became a Catholic he said he had been partly influenced by Ronald Knox.

After Knox became a Catholic priest, he wrote and broadcast about Christianity and other subjects. He became a Roman Catholic chaplain at Oxford University in 1926 and in 1936 was elevated to the title of Monsignor. He began writing classic detective stories while a chaplain at Oxford.

This was during what is now referred to as the Golden Age of Detective Fiction in the 1920s and 1930s and Knox was one of the founding members of the Detection Club.

A picture taken at a 1932 meeting of the Detection
Club, when G K Chesterton was president

This elite club was formed in 1930 by a group of British mystery writers that included Agatha Christie, Dorothy L Sayers and many other famous authors. Anthony Berkeley was instrumental in setting up the club and the first president was G K Chesterton.

The members of the Detection Club agreed to adhere to Knox’s Commandments in their writing to give the reader a fair chance of guessing who was the guilty party.

These ‘fair play’ rules were summarised by Knox in the preface to Best Detective Stories 1928-29, which he edited.

Knox’s Ten Commandments, or Decalogue, are as follows:

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.

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 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 which he may discover.

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.

10. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them.

According to Knox, a detective story ‘must have as its main interest the unravelling of a mystery, 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 Murder Room's edition of
Knox's first detective novel

As a matter of clarification, in the light of modern-day sensitivities, the reasoning behind rule number five is that magazine stories in 1920s so often portrayed criminal masterminds as being of Chinese ethnicity that it had become something of a cliché, one that Knox believed was best avoided.

Knox was a prolific satirical writer and wrote many essays and books about religion.

He also wrote some crime short stories and six detective novels: The Viaduct Murder (1926), The Three Taps (1927), The Footsteps at the Lock (1928), The Body in the Silo (1933), Still Dead (1934), Double Cross Purposes (1937).

Paperback editions of all six detective novels were published by the former Orion imprint The Murder Room in 2013 and are still available from Amazon and Waterstones.

He also contributed to three collaboration works by the Detection Club; Behind the Screen (1930), The Floating Admiral (1931) and Six Against the Yard (1936).

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