Clues--what are they?

By following clues Sherlock Holmes can reconstruct a crime, a secret message, or even--if he works at it and is lucky enough--some law governing the workings of nature. What are they, these things we call clues? Why are they there? Why is it that they can lead us to things which initially we did not know?

Can we call just anything a clue? Criminals know that if they leave clues behind they run the risk of being caught. Can they, before they leave the crime scene, decree all clues to disappear?

Anyone who tries to play Sherlock Holmes will recognize the importance of clues. The word 'clue'--or some equivalent--they know is not a label we can apply to anything we please. Whether something is a clue in a particular case is a question with an objective answer. Indeed detectives distinguish between genuine clues and false clues (the practice at Sherlock Holmes's time was to call a false clue a blind). It is not a pleasant experience mistaking a false clue for genuine.

But what are they? What are clues? Why do they have this ability of leading us on, towards the truth?

Let's try to answer this question by going backwards; let's reason in the following way. Clues help us to reconstruct. To make things easier let us suppose the thing we want to reconstruct is not a crime but an ancient sailing ship. Some authors have mentioned this kind of sailing ship here and there but none has given a detailed account. In fact, so far as we know no one has come across even a single crude drawing. What should we do?

Naturally, the first thing we do is look for more information. We will scour books and museums and even archaeological sites to see what clues we can find, clues that will help us build this sailing ship.

What do we expect these clues to tell us if we should find any?
If we are to succeed in reconstructing this sailing ship, the clues we hope we will find will, eventually, have to tell us as many of the characteristics of this ancient sailing ship as we require. How big are these ships? How much can they hold? Can they go on the open sea or are they confined to shallow waters? We will have many questions like these and enough of them will have to be answered before we can go ahead and start building. This is of course a tall order, the reason why the chance of success in this kind of projects is seldom very high.

To build a sailing ship we need to know enough of its characteristics. A sailing ship is not a pile of timber with a piece of fabric thrown in. A sailing ship has a structure. Each kind of sailing ship has its own kind of structure with its own set characteristics. If we know enough of the characteristics of a sailing ship we can rebuild that kind of sailing ship. In the case of our sailing ship, there is no hope of our ever finding a blueprint. Because it is ancient we can find out its characteristics only through clues. Now the clues will not tell us directly what these characteristics are (because if they will, we will not call them clues) but eventually they will if they are to be useful at all.

So what are clues?

From our example we can see they are simply the characteristics of the structures we want to reconstruct, hidden behind some sort of disguise. We are using the word 'disguise' metaphorically to signify that clues do not tell us automatically what is behind them; we have to figure it out; we have to remove the disguise.

Which of course is usually the difficult part! But difficult or not, this is what clues are. They the characteristics of structures, disguised. This is the reason why by following them we can decipher secret messages. For those who send messages have to use a language. Now each language has its own structure with its own set of characteristics. For example, one of the characteristics of the English language is that of the twenty-six letters in the English alphabet E is the most frequently used. As we all know, this characteristic is often depended upon when deciphering English messages. In cracking the Dancing Men Cipher the first thing Sherlock Holmes did was to see which of the Dancing Men appeared most frequently in the intercepted messages. That Dancing Man is a clue. Behind it is the letter E.

Now just as a language has a structure, so does a crime. When a person is shot she falls. From the way she falls we can estimate the direction from which the shot comes. Thus it is that when Sherlock Holmes investigates a crime he will examine the crime scene carefully to see what clues he can find and basing on his knowledge of the characteristics of the various sorts of things he knows, figure out the meanings of these clues.

Scientists follow clues too. Why do the planets move around the sun in ellipses? Newton was able to work out mathematically that this is a characteristic of a universe governed by the theory of universal gravitation as he has formulated it, together with his three laws of motion.

In playing Sherlock Holmes we are trying to reconstruct structures we cannot see. To this end we have to follow clues because the clues are the characteristics of these structures, even though disguised.