Borges suggested that the classic sort of detective story belonged to the genre of fantasy, not of realism, though it comes from intelligence and not from mere imagination. This genre is not realistic, because it rests on the assumption that crimes are detected by observation and reasoning, rather than by tip-offs and confessions, as happens in reality. The detective in these stories is like a sort of chess grand master, who guesses all the steps that have led the adversary - the killer - to make his lethal move, and counteracts him: checkmate. His clairvoyance leaves us amazed and a little annoyed, like a sleight-of-hand trick. But it also produces a mental pleasure that has something addictive to it.
The best protagonist of an intellectual tour-de-force, however, is not the spectacularly infallible sleuth, but the modest, grey, sharp-eyed observer, whose perspicacity nobody suspects and whose personality appears contemptible, such as Chesterton's Father Brown or the disheveled Colombo. We cannot, and would not, ever dream of disparaging the brilliance of Sherlock Holmes, of course - but even his admirers find him just a little oppressive, even laughable. E. C. Bentley, a great friend of Chesterton (who dedicated The Man Who Was Thursday to him), wrote Trent's Last Case to question the pure use of intelligence in a genre that is intelligent par excellence. Chesterton himself of course, but also Agatha Christie and Dorothy L. Sayers, considered this novel - never translated into Spanish, as far as I know - as the best of the best, because it reasonably questions the passion for reasoning.
For Borges, the detective story's vocation of intelligence favors an implicit metaphysical aspect, which he developed in Death and the Compass. After all, philosophy itself is a sort of murder investigation, which inexorably has to be undertaken by the victim himself: Who will kill me - time, nature, God - or will it be suicide? However, the evolution of the genre has blurred its character as an intellectual charade, shifting it into a field that is far less abstract, and unpropitious to speculation: that of sociology.
It all began with the American style of noir novel, begun by Edgar Wallace and culminating in Dashiell Hammet and Raymond Chandler. Deep down, these are not so much detective stories as adventure classics, in which the beasts and pirates of yesteryear have been replaced by gangsters in the asphalt jungle. Ambushes, shoot-outs and fistfights gradually displace the calm of pure reasoning. What holds our attention is not the mechanism of the crime and the identity of the perpetrator, but the social conditions that underlie it. The old uncertainty fades, because we now know that whoever does the killing, the culprit is always the same: capitalism.
The latest addition to the genre is the trend to tourism. Newer crime novels may be lacking in originality, but never in scenery. They happen in India, South Africa, Israel and Scandinavia. They also practice time-tourism, and we have seen detectives who live in the age of Nero, or Darwin. I have read an intrigue that is cleared up by Newton, and another by no less than Dante Alighieri.
I am sorry to say that the manners of the criminals, and above all their capacity to intrigue, have gained little by all these frills. But what we lose in quality we gain in quantity. Agatha Christie kept us riveted with one murder, but now we need the killing of a whole family in each chapter or we start to yawn. All killers are serial killers, who work on an assembly-line basis. But we veteran fans yearn for the deceptive tranquility of the cottage setting, the furtive hand that drops arsenic in the teacup, the mental challenge of those writers who, like the devil in Macbeth, could lead us down false paths with the true words.