Clue, n.: Something that serves to guide or direct in the solving of a mystery. Most predominately used in detective fictions to indicate the evidence through which a crime is solved.

Etymologically, clue (earlier clew) derives from the Indo-European gleu – to gather into a mass, from which we also derive the English words glue and clay. As a clew (the spelling used by Sir Arthur Conan Doyle in his Sherlock Holmes stories), the word more specifically refers to the collected mass of a ball of thread. Thread, clay, gluey mass; the question is how these seemingly unconnected roots and relations of the word clue might shed light on the particular mode of analytical or deductive thought utilized by both fictional detectives and people in their everyday lives.

The shift in meaning from a collected mass to something that serves to guide seems to first occur in early translations of the ancient Greek myth of Theseus in the labyrinth at Crete. In this story, the princess Ariadne gives the hero a clew, a ball of thread that Theseus unravels behind him in order to find his way back out of the Minotaur’s maze – the way detectives will later use clues to unwind the labyrinths of the criminal underworld and psyche.

The metaphor of clue as a thread is indicated in the first detective story, Poe’s “The Murders in the Rue Morgue,” when the detective Dupin displays his analytical powers by tracing back the thread of the narrator’s thought step for step. Though he uses this method of ratiocination to solve the titular murders, the clues provided for the solution of the crime are oddly presented all at once. As the genre developed, however, clues become increasingly deployed as a thread to follow, the discovery and interpretation of each clue leading the detective on to the next. This also leads to the conventional narrative structure of most detective stories, in which the revelation of the significant clues provides the key tangles or dramatic moments in the thread of the plot.

The etymological connection between clue and clay may at first seem obscure, but begins to make sense when considering the nature of clay as indistinct and malleable. In the earliest detective stories – from Poe and Doyle to the Golden Age of mystery fiction represented by Christie and Sayers – most clues were unfortunately too obvious or absurd. What the detective notices is what most pointedly stands out, what is peculiar, singular, outré – poisoned daggers, over-the-top costumes, grisly deaths. As the genre developed into the hardboiled American PI stories, there was a shift toward more realistic representations of the detective and their methods, as well as the way in which clues are deployed and discovered.

In the fictions of Hammett and Chandler, for instance, the key clues are often indistinct or subtle – a slight gesture or expression, a business card accidentally discovered in the victim’s pocket – and the detective is often unaware when a key piece of evidence comes to hand unless they are vigilantly observant. These are the kinds of marks left in the course of real crimes. Even more significantly, clues are malleable and thus require interpretation. There is no longer a clear 1:1 relationship between a clue and its significance for the crime. Instead clues become relevant in the way that they allow the known facts of the case to be molded into increasingly more convincing hypothetical solutions. This clay-like quality of clues also allows them to be misinterpreted or misleading. No longer is there a direct thread through a unicursal (single path) labyrinth, but a maze with those devious dead ends called red herrings.

While I am personally less familiar with the more recent trends in detective fiction – the police procedural made popular in such shows as CSI – they continue the realistic representations began in the hardboiled era, including now the legal processes necessary for successful criminal investigation. It is here that the clue as glue, and its original roots as a collected mass, again becomes relevant. In order for a given clue to be considered as evidence in a criminal case (the glue that holds the case together), a clue cannot be considered on its own. Rather, a case is constructed be gathering together enough evidence (properly interpreted) that amasses into an irrefutable argument describing the motives and methods behind the crime.

The representation of the legal process is, of course, far more realistic than the earliest depictions of deductive work. But while Poe’s description of ratiocination paints it as outré as the earliest uses of clues, outside the bounds of literature such rational analysis is actually quite commonplace. In light of the steps necessary to build a criminal case, any rational argument that is constructed through the gathering and weighing of evidence into a followable thread of thought – whether in investigative reporting or writing a school essay – could be seen as akin to detective work, or at least the deductive analytical power. Philosophically, there is a centuries-old assertion that we similarly observe and interpret causal evidence in order to make sense of the world around us on a daily basis – whether we’re looking out a window to see if we need to bring an umbrella, or when noting someone’s facial expression to determine their mood, each of these provides clues connecting events and actions.

I won’t rehash here the case against the analytical faculty – which ranges from complaints that no one really thinks like Dupin or Holmes to a misunderstanding that critical analysis is in some way divisionary. Wordsworth, for instance, called analytical reasoning “the brain that divides,” though the way in which we psychologically handle clues suggests instead it is the brain that pieces together and puzzles out. One significant argument that the etymology of clues in detective fiction may help us refute is that analysis demands proof in the form of physical or material evidence. If so, then deduction is an inappropriate technique for interpreting situations where no tangible proof is available, such as in questions of spirituality and belief. The assumption here is that clues can only be empirical; but another recent trend in mystery fiction – the supernatural detective story – suggests instead that there are types of evidence that are not scientifically verifiable, but still provide valid clues to the solution of both real crimes and metaphysical quandaries.

In short, for those who know how to look the world is full of clues of every color and stripe. And if we observe, gather, interpret, and follow their trails, who knows out of what labyrinths of uncertainty and doubt we might be led.

The defense rests its case.