Father Ronald Knox's List

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In Best Detective Stories for 1939 Father Ronald Knox published his "Ten Commandments for Detective Fiction." Knox was a detective story critic, fan, writer, and a founding member of The Detection Club (a group of British mystery writers), so he knew whereof he spake. He was not entirely serious; he knew that there are more than ten rules and that they can all be broken. But to a Roman Catholic priest, the idea of Ten Commandments was ineluctable.

I've just done an update of the list for the modern writer/reader in The Writer magazine, but they didn't have space to print the original.

Knox's list is usually reprinted in abridged form, but here is the original with all the surrounding verbiage:

What is a detective story? The title must not be applied indiscriminately to all romances in which a detective, whether professional or amateur, plays a leading part. You might write a novel the hero of which was a professional detective, who did not get on with his wife, and therefore ran away with somebody else's in chapter 58, as is the wont of heroes in modern novels. That would not be a detective story. 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.

And here, for my own part, I would draw a very clear line of demarcation between detective stories and 'shockers'. Shockers are not in the true sense mystery stories at all; they do not arouse a human instinct of curiosity. Suppose that I go into a night - club, where a fascinating woman with green eyes drops her handkerchief near me in passing out, and, as I politely stoop to pick it up, whispers to me 'For God's sake keep clear of 568 Cromwell Gardens, and, if you are ever set upon by thugs on the stairs of the Down Street tube station, remember to ask them for the counter - sign of the Pink Spot' - all that, which is the practically invariable opening of what I call shockers, does not genuinely excite curiosity. It is not a mystery; it is simply an obvious lie. People would not say that kind of thing to me, and I should not take the trouble to go all the way to Cromwell Gardens if they did. We know at once that the woman is an adventuress, probably a quite innocent adventuress who is being compelled by a threat of blackmail to subserve the purposes of villains; that there is a gang of international crooks at work, determined to put an end to the peace of Europe by giving away English state secrets to an unknown foreign power. We are certain beforehand that the motives of the villains will be entirely inhuman, the actions of the hero and heroine rash to the verge of idiocy; that the complications to which we are introduced at the beginning will not be explained at the end, because by that time the reader will have forgotten all about them, and probably the author as well. All this is not a detective story.

The true essence of a detective story - I am thinking for the moment of those which occupy a whole volume; we will come to the short story later on - is that in it the action takes place before the story begins. Of course, it is well to have some kind of introduction which brings the main characters on to the stage, and gives us some touch of their quality. Indeed, it seems to me a weakness in Mr. Freeman Wills Croft that he usually presents us at the very outset with the body of a total stranger - he has missed at once all his chance of evoking our human sympathy; nor does it improve the situation when we discover later on in the book, as we are apt to do, that it was really a totally different total stranger all the time. But in the third chapter, at latest, of a detective novel the curtain should suddenly go up on a crime, preferably a murder, already committed, ripe for investigation. The real action of the book is now over; incidents may still occur, but the horror and violence are already at an end before the great detective appears on the scene. The story derives its excitement only from the danger of the criminal getting off scot free, or of some innocent person being condemned in his place. It will be seen, therefore, that the detective story differs essentially from every other type of fiction. For the interest of the ordinary romance centres in the question, 'What will happen?' - unless you include the modern sex novel, where the interest centres in the question, 'Will anything ever happen?' But the interest of the detective romance centres in the question 'What has happened?' It is a hysteron - proteron in the Homeric manner.

Ordinary romance was invented, one would think, by a wearied historian, who, finding himself (like most historians) unable to give a true account of the past, and willing (unlike most historians) to confess his inability, sat down to write a kind of literature in which all his characters behaved exactly as he wanted them to, because they had no existence outside his own brain. Whereas one would suppose the first writer of detective fiction to have been a scientist, who, giving up the riddles of his own craft, which either defied explanation or opened out fresh vistas of problems demanding fresh explanations, determined to set himself a problem which he could solve, because he and no other was responsible for the inventing of it. Ordinary fiction appeals to the synthetic in our natures, detective fiction to the analytic; ordinary fiction works forwards from the conditions of the plot to its consummation, detective fiction backwards from the consummation to the conditions.

It seems a pity that somebody cannot invent a kind of crook film in which the crime will be enacted in front of the camera exactly as it took place, but will be turned into a mystery by the simple expedient of releasing the film backwards. So highly specialized a form of art will need, clearly, specialized rules. And the detective author, alone among authors, cannot even in this libertine age afford to break the rules. The moderns will attempt to write poetry without rhyme or metre, novels without plot, prose without sense; they may be right or wrong, but such liberties must not be taken in the field of which we are speaking. You cannot write a Gertrude Stein detective story. For the detective story is a game between two players, the author of the one part and the reader of the other part. The reader has scored if, say, half - way through the book he has laid his hand on the right person as the criminal, or has inferred the exact method by which the crime was perpetrated, in defiance of the author's mystifications. The author on his side counts the victory, if he succeeds in keeping the reader in a state of suspended judgment over the criminal, or complete mystification over the method, right up to the last chapter; and yet can show the reader how he ought to have solved the mystery with the light given him.

As with the acrostic, as with the cross - word competition, honourable victory can be achieved only if the clues were 'fair'. Thus, when we say that the detective story has rules, we do not mean rules in the sense in which poetry has rules, but rules in the sense in which cricket has rules - a far more impressive consideration to the ordinary Englishman. The man who writes a detective story which is 'unfair' is not simply pronounced guilty of an error in taste. He has played foul, and the referee orders him off the field. I laid down long ago certain main rules, which I reproduce here with a certain amount of commentary; not all critics will be agreed as to their universality or as to their general importance, but I think most detective 'fans' will recognize that these principles, or something like them, are necessary to the full enjoyment of a detective story. I say 'the full enjoyment'; we cannot expect complete conformity from all writers, and indeed some of the stories selected in this very volume transgress the rules noticeably. Let them stand for what they are worth.

I. 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. The mysterious stranger who turns up from nowhere in particular, from a ship as often as not, whose existence the reader had no means of suspecting from the outset, spoils the play altogether. The second half of the rule is more difficult to state precisely, especially in view of some remarkable performances by Mrs. Christie. It would be more exact to say that the author must not imply an attitude of mystification in the character who turns out to be the criminal.

II. All supernatural or preternatural agencies are ruled out as a matter of course. To solve a detective problem by such means would be like winning a race on the river by the use of a concealed motor - engine. And here I venture to think there is a limitation about Mr. Chesterton's Father Brown stories. He nearly always tries to put us off the scent by suggesting that the crime must have been done by magic; and we know that he is too good a sportsman to fall back upon such a solution. Consequently, although we seldom guess the answer to his riddles, we usually miss the thrill of having suspected the wrong person.

III. Not more than one secret room or passage is allowable. I would add that a secret passage should not be brought in at all unless the action takes place in the kind of house where such devices might be expected. When I introduced one into a book myself, I was careful to point out beforehand that the house had belonged to Catholics in penal times. Mr. Milne's secret passage in the Red House Mystery is hardly fair; if a modern house were so equipped - and it would be villainously expensive - all the countryside would be quite certain to know about it.

IV. No hitherto undiscovered poisons may be used, nor any appliance which will need a long scientific explanation at the end. There may be undiscovered poisons with quite unexpected reactions on the human system, but they have not been discovered yet, and until they are they must not be utilized in fiction; it is not cricket. Nearly all the cases of Dr. Thorndyke, as recorded by Mr. Austin Freeman, have the minor medical blemish; you have to go through a long science lecture at the end of the story in order to understand how clever the mystery was.

V. No Chinaman must figure in the story. Why this should be so I do not know, unless we can find a reason for it in our western habit of assuming that the Celestial is over - equipped in the matter of brains, and under - equipped in the matter of morals. I only offer it as a fact of observation that, if you are turning over the pages of a book and come across some mention of 'the slit - like eyes of Chin Loo', you had best put it down at once; it is bad. The only exception which occurs to my mind - there are probably others - is Lord Ernest Hamilton's Four Tragedies of Memworth.

VI. No accident must ever help the detective, nor must he ever have an unaccountable intuition which proves to be right. That is perhaps too strongly stated; it is legitimate for the detective to have inspirations which he afterwards verifies, before he acts on them, by genuine investigation. And again, he will naturally have moments of clear vision, in which the bearings of the observations hitherto made will become suddenly evident to him. But he must not be allowed, for example, to look for the lost will in the works of the grandfather clock because an unaccountable instinct tells him that that is the right place to search. He must look there because he realizes that that is where he would have hidden it himself if he had been in the criminal's place. And in general it should be observed that every detail of his thought - process, not merely the main outline of it, should be conscientiously audited when the explanation comes along at the end.

VII. The detective must not himself commit the crime. This applies only where the author personally vouches for the statement that the detective is a detective; a criminal may legitimately dress up as a detective, as in the Secret of Chimneys, and delude the other actors in the story with forged references.

VIII. The detective must not light on any clues are not instantly produced for the inspection of the reader. Any writer can make a mystery by telling us that at this point the great Picklock Holes suddenly bent down and picked up from the ground an object which he refused to let his friend see. He whispers 'Ha!' and his face grows grave - all that is illegitimate mystery - making. The skill of the detective author consists in being able to produce his clues and flourish them defiantly in our faces: 'There!' he says, 'what do you make of that?' and we make nothing.

IX. 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. This is a rule of perfection; it is not of the esse of the detective story to have a Watson at all. But if he does exist, he exists for the purpose of letting the reader have a sparring partner, as it were, against whom he can pit his brains. 'I may have been a fool,' he says to himself as he puts the book down, 'but at least I wasn't such a doddering fool as poor old Watson.'

X. Twin brothers, and doubles generally, must not appear unless we have been duly prepared for them. The dodge is too easy, and the supposition too improbable. I would add as a rider, that no criminal should be credited with exceptional powers of disguise unless we have had fair warning that he or she was accustomed to making up for the stage. How admirably is this indicated, for example, in Trent's Last Case!

This Decalogue is, I suspect, far from exhaustive; no doubt but my reader is all agog to add a few more prohibitions to the list. Rules so numerous and so stringent cannot fail to cramp the style of the author, and make the practice of the art not difficult only, but progressively more difficult. Nobody can have failed to notice that while the public demand for mystery stories remains unshaken, the faculty for writing a good mystery story is rare, and the means of writing one with any symptom of originality about it becomes rarer with each succeeding year. The game is getting played out; before long, it is to be feared, all the possible combinations will have been used up.

Senor Capablanca has recently appealed for a brighter chess, with a larger number of squares on the board. But in what conceivable way are we to enlarge the horizons of this far more intriguing game, the solving of detective problems? What step of progress can we make, but will land us either in technicalities or in impossibilities? Even the exterior setting of the thing is in danger of becoming stereotyped. We know, as we sit down to the book, that a foul murder has almost certainly been done at a country house; that the butler will have been with the family for sixteen years; that a young male secretary will have recently been engaged; that the chauffeur will have gone away for the night to visit his widowed mother. If life were like the detective stories, it would be almost impossible for the father of a chauffeur to insure his life on any terms. We know that the victim, if he is a man, will have been killed either in the shrubbery or in his own study, with a wound at the back of his head; if she is a woman she will be found dead in her bedroom, with an overdose of sleeping - draught to account for it all.

We know that at least three members of the house - party will have been wandering about the passages in a suspicious manner during the small hours. We know that some piece of writing has been left, usually on a blotter or on the next telegraph form, which is to throw light on the business, or else dust in the reader's eyes; and so on. If I walked into the detective - story house, I believe I should be able to find my way about it perfectly; it is always more or less the same in design - an embarrassing one, because the bedrooms all open out of one another. But far more serious than this monotony of setting is the growing difficulty, for the author, of finding ways in which he can deceive his reader without either breaking the rules, or using gambits which have been used ad nauseam before. I forget where it is that Mr. Bernard Shaw describes the growth of naval armaments as a senseless and unending competition between the theory of attack and the theory of defence. A spends money on torpedoes, and B has to spend money on torpedo - destroyers; B invents a new form of mine, and A has to lay down a new type of minesweeper. So it is with batting and bowling in cricket; so it is with serving and returning serves in tennis; attack and defence improve alternately, under the stress of mutual competition.

And so it is with the great detective game; the stories become cleverer and cleverer, but the readers are becoming cleverer and cleverer too; it is almost impossible nowadays to think out any system of bluff which the seasoned reader will not see through. Thus, in the old days, when a woman was found very uncomfortably bound to a chair, with her mouth gagged, and possibly only just recovering from the effects of an anaesthetic, we used to suppose, not unnaturally, that she had been tied up like that by villains. Now we assume as a certainty that she is in league with the villains, and all the tying - up business was merely a plant; we have had the old bluff worked off on us so many times that it fails to take us in. Again, when the room is found covered with fingermarks or the lawn with foot - prints, we know at once that these are false clues, arranged by the criminal so as to throw suspicion on an innocent person.

That overdose of chloral has long ceased to have any mystery for us; there will be a half - empty bottle of it by the bedside, and the stomach of the deceased will be a mass of chloral, but we know for a dead certainty that the murder was effected somehow else, and the chloral introduced into the system by a special process - after death as likely as not. The dead man found in the grounds was not murdered in the grounds; he was murdered miles away, and the corpse was brought there in a motor. The moment we come across any mention of a scapegrace brother who is supposed to have died in Canada, we know that he did not really die; he is going to reappear, either as the villain or as the victim, and will be mistaken for the original brother every time. The fact that there were signs of a struggle in the room always means that there was no struggle, and the furniture was deliberately thrown about afterwards; the fact that the window was left open is proof positive that the crime was committed by somebody living in the house. All messages which come over the telephone are fake messages; people who are overheard telephoning in their rooms have never really taken the receiver off.

The possession of a good, water - tight alibi is perhaps the surest mark of the real criminal; the man who has wandered aimlessly about the streets of London for three and a half hours without meeting anyone who could swear to his identity is no less certainly innocent. Gone, too, are the old familiar tests by which, in the Victorian days, we used to know the good characters from the bad. Neither age nor sex is spared; the old country Squire, who is a J.P., and has for years held his head high among his neighbours, so good, so kind, so charitable - watch him! The heroine, even, the friendless and penniless female who looks up with such appealing eyes into the face of the detective's friend, may quite possibly be a murderess; provocation she has had, it may be, but there is no question that she handled the blunt instrument in a workmanlike manner. The only person who is really scratch on morals is the aged butler; I cannot off - hand recall any lapse of virtue on the part of a man who has been with the family for sixteen years. But I may be wrong; I have not read all the detective stories.

It is possible that we shall get, before long, into a stage of double bluff, when the author will make his heroes look like heroes and his villains look like villains in the certainty that the over - ingenious reader will get it the wrong way round. Indeed, I did myself once write a story in which the curate was perfectly innocent and the dark, sinister man committed the murder; but I was before my time, and the public thought it inartistic. Before long, no other form of concealment will be possible; and we cannot proceed from double bluff to treble bluff and so on indefinitely; the thing would become merely tiresome.

If this danger of stagnation threatens the full - dress detective novel, it threatens, a fordori, the 'short' detective story. The short story must always take an honourable place in detective fiction; it is the medium which has given us some of the best Holmes literature, and the whole cycle of Father Brown. But it labours under an obvious disadvantage as compared with the full armchair performance. There are three questions which may call for solution in any criminal mystery - Who did it? Why did he do it? How did he do it? The short story has sufficient elbow - room to deal with the question of method - how did the man come to be murdered when he was sitting alone in a hermetically sealed room? How was the victim persuaded to walk over the edge of the cliff? How were the lumps of coal substituted for the rubies in a registered parcel on its way between London and Paris? - and so on. It is far more difficult to create, in such short compass, a genuine doubt as to the motive with which the crime was done, or the identity of the criminal. It is difficult even for a Chesterton to introduce us to half - a - dozen characters whose allotted span of life is a bare thirty pages, and tell us enough about them to make the spotting of the criminal a logical possibility. And that is the reason, I suppose, why some of the most conscientious writers (such as Mr. Cole and Mrs. Christie) always seem to be at their best when they have a whole volume at their disposal for developing a single theme.

The short story, then, will ordinarily deal with a mystery of method; and it is precisely here that the possibilities are most in danger of exhaustion, precisely here that originality is most difficult. Some of the stories in this collection deal, ingeniously enough, with the question of identity, but I do not think there is one of them which really keeps the reader on tenterhooks of excitement wondering who did it. I have an uneasy suspicion that the day of the old, 'straight' detective episode is done; that there can be no more murders in the Rue Morgue which can baffle the Surete, because it has all been done before and there is nothing new under the sun; that Dr. Roylott will never persuade another step - daughter to sleep in the room with the ventilator, nor any charitable coppers fall into the bowl of Neville St. Clair. Professor Moriarty, he is dead; all our friends are lapped in lead - or am I too pessimistic? Anyhow, there is a marked tendency in the stories which compose this collection to strike out new lines of treatment, to desert the stereotyped formula prescribed, we thought, once for all by Sir Arthur Conan Doyle. Not one of them makes any real attempt to introduce a Great Detective, with outlandish characteristics and a habit of snubbing everybody all round - time was when we regarded such a figure as indispensable; a fortiori, not one of them includes a Watson.

Mrs. Christie goes further; she presents us with a mystery which is solved by the stupidest member of the party, who happens to have special knowledge of the technicalities bearing on the point. In the whole collection you will find, I fear, no honest lens - and - forceps work, except perhaps in 'The Late Edition'. That sort of thing seems to be out of favour with the magazines. Ingenuity tends to replace mystery; 'Under a Thousand Eyes', for example, has the materials rather than the make - up of a mystery story. Yet all the stories (I hope it will be admitted) are detective stories in the broader sense; not one but proclaims in some new form the old, optimistic slogan of humanity, 'Murder will out'.

The true detective fan is constantly asking himself, I take if, the following question: 'Have I now arrived at the point in this story at which I ought to stop, put the book down, light a fresh pipe, take a turn round the garden, and try to solve the mystery for myself before I read on further?' If he decides on such a course of action too soon, he will make the mistake, a capital mistake according to Holmes, of theorizing ahead of his data. If he decides on it too late, he will find that the author had already started explaining things, and victory is thus robbed of its bloom. I am venturing, therefore, to suggest here the points in the various stories at which, so it seems to me, the reader may profitably devote himself to the task of solution. I need hardly say that since I was reading the stories in the way of business I did not attempt this method, and doubtless I shall be wrong in many cases. But those who read this introduction first - alas, how few people there are who read the introduction first! - will perhaps be grateful for being given this chance of exercising their ingenuity.

I shall give in each case a cue, the last few words of a sentence; on reaching those words let the reader switch his eyes off the page at once, for fear of finding out too much before he attempts the solution for himself. In 'Trial by Ordeal', there is no caesura. The same is true of 'A Race for Life'. In 'The Artificial Mole' stop at ' he had been too clever for us'. In 'The Secret of the Mountain', at '.. shut his eyes in order to go over'. In 'The Master Touch', no caesura. In 'Through the Window', at '... Which - as there was nothing more that could be done - it was'. In 'The Poison Bottle', at the words '... Look at the papers'. In 'The Tuesday Night Club', at '... Will you speak first? he said'. In 'The Diary of Death', stop at 'his eccentric friend's promise'. In 'Under a Thousand Eyes', no caesura. The same is true of 'Mr. Leggatt leaves his Card'. In 'Who killed Castelvetri?' stop before paragraph III. (But there is not much satisfaction to be got here.) In 'The Late Edition', at '.. or are you stopping here?' (But the reader will probably have guessed before this.) In 'The Night of the Garter', stop at the words '... No one will ever see the “Luck” of Rappley again, he said'. In 'The Sign of Seven', at '... Die as yourself, you swine!' In 'Drops that Trickle Away', at '.. she was left penniless'. In 'An Artist in Crime' stop, if you will, at '... Just in his spare time you know'. But this is not a formal mystery story. In 'Blackman's Wood' it is impossible to mark any precise caesura. In 'Overwhelming Evidence', at '... The punishment of the true evil - doers had been brought about'. (But you will have guessed earlier.) In 'The Langdon Case', stop at '.. reprieved on the score of insanity'.

But I must say no more. It is not for the anthologist to crush, heavy - handed, all the juice and sweetness out of the flowers he has garnered before the bouquet is handed over. More especially, when he deals with such frail blooms as mystery stories, that yield their scent but once, and then, desiccated, lose all save a botanical interest. When I was about to read one of the greatest detective novels of our time, my present collaborator said to me, 'I wonder if you will think it fair?' - no more than that; and I, greatly to be pitied, solved the problem at the first sentence. I will be silent, and let the reader cut the pages for himself with the sharper edge of his own intelligence.

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A Lord Darcy novel
Mystery - Moriarty
The 4th in the "Moriarty" series
Third in the "Professor Moriarty" series

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