The 10 Commandments of Detective Fiction

Monsignor Ronald Knox is best known to Sherlockians as the author of "Studies in the Literature of Sherlock Holmes," which he wrote in 1911. Vincent Starrett mentioned this essay at least three times in his "Books Alive" column in The Chicago Tribune.

But Knox was also a theologian, translator of the Bible, and mystery writer. He even wrote his own  10 Commandments of detective fiction.  I stumbled onto a blog post recently in which the writer was mercilessly critical and dismissive of this Decalogue. I think she missed the point that the list was every bit as tongue-in-cheek as Knox's writings about Sherlock Holmes. Keep that in mind as you read:

1. The criminal must be someone 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 must not himself commit the crime.
8. The detective must not light on any clues which are not instantly produced for the inspection of the reader.
9. The stupid friend of the detective, the Watson, must not conceal 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.

This list came to mind a couple of weeks ago during a meeting of the Tankerville Club, the scion society to which I belong. Our founder and Official Secretary recalled another meeting some years before during which a member of our group rather loudly declaimed Commandment No. 5. This was a source of embarrassment to the other members not only because it's racist, but also because the restaurant at which we were meeting was a Chinese one!

How many of these commandments are violated in the Canon? I'd say at least two -- numbers 1 and 8. Are there any other violations that I'm forgetting?