It's easy to see Sherlock Holmes as a hard, cold reasoning machine: the epitome of calculating logic. And it's true. In many ways, the ideal Holmes is almost a precursor to the computer, taking in countless data points as a matter of course, analyzing them with startling precision, and spitting out a solution. But Holmes has one element that a computer lacks, and it is that very element that both makes him what he is and undercuts the image of the detective as nothing more than logician par excellence: imagination.

Imagination and intuition--in combination, of course, with good old logic--form the cornerstone of Holmes's successes in cases where others fail. These qualities help him see beyond the obvious and teach him where and how to look.

What happens with a lack of imagination?

Over and over, Holmes faults those who lack imagination. In "Silver Blaze," he dismisses Inspector Gregory's attempts at a solution to the mystery of the missing horse and murdered trainer, telling Watson, "Inspector Gregory, to whom the case has been committed, is an extremely competent officer. Were he but gifted with imagination he might rise to great heights of his profession. On his arrival he promptly found and arrested the man upon whom suspicion naturally rested."

What does Gregory, with all his competence, immediately do? Arrest the most likely suspect, without further thought. True, the most likely suspect may end being the actual perpetrator of the crime; but how will Gregory know, if he fails to imagine other, less obvious alternatives? Absent imagination, he jumps the gun.

In "The Adventure of the Norwood Builder," Holmes faults Lestrade just as he faulted Gregory. When Lestrade has finished his reasoning on the case, he asks the detective, "Is not all this obvious?" To which, Holmes responds, "It strikes me, my good Lestrade, as just a trifle too obvious. You do not add imagination to your other great qualities, man, but if you could for one moment put yourself in the place of this young man, would you choose the very night after the will had been made to commit your crime?"

Just like Gregory, Lestrade grasps for the most ready solution, the obvious way to go about the case. But in neither instance does the obvious approach cover the necessary facts - and in Lestrade's case, it seems to go against what we know about basic human nature (Would someone really kill a man who has just willed him all of his money, the very same night the will is created? Holmes's skepticism is well warranted).

A lack of imagination can thus lead to both faulty action (the arrest or suspicion of the wrong man, in both instances explored here) and to the lack of proper action (looking for the actual culprit). If only the most obvious solution is sought, the correct one might never be found at all.

And what happens in its presence?

On the flipside, Holmes pays one of his rare compliments to Inspector Baynes, in "The Adventure of Wisteria Lodge," when he comments that, "You will rise high in your profession. You have instinct and intuition."

What did Baynes do differently from his Scotland Yard counterparts? He anticipated human nature instead of dismissing it, arresting the wrong man on purpose with the goal of lulling the real criminal into false complacency. And in this anticipation lies one of the main virtues of an imaginative approach, one that goes beyond simple logic in interpreting facts and instead uses that same logic to create hypothetical alternatives: things that might occur given a certain action (the complacency of a criminal if he thinks someone has already been arrested for the crime) and things that might have occurred given the facts at hand.

For an example of the latter, we turn once more to "Silver Blaze." When Holmes and Watson fall upon the track of the missing horse, Holmes remarks, "See the value of imagination. It is the one quality which Gregory lacks. We imagined what might have happened, acted upon the supposition, and find ourselves justified. Let us proceed." Holmes and Watson would have never fallen upon the proper track had they not first imagined where that track might lie, using logic to create a hypothetical scenario that, at the time they created it, had no facts other than reason and intuition to support it.

The candle and the tacks: An instance of imagination at work

In both instances--the drawbacks of a lack of imagination and the benefits of its presence--the experimental psychology literature bears out Holmes's insight.

Take this classic study, created by the Gestaltist Karl Duncker and originally published in Psychological Monographs in 1945. You are led into a room with a table. On the table are three items: a box of tacks, a book of matches, and a candle. Your assignment: attach the candle to the wall. How do you proceed?

If you are like over 75% of the participants, you may try one of two routes. First, you might try to tack the candle onto the wall. You'll quickly find that method to be futile. Or, you might try to light the candle and use the dripping wax to attach it to the wall, foregoing the box of tacks entirely (after all, you might think, it could be a distracter!). Again, you'd fail. The wax is not strong enough to hold the candle and your contraption will collapse. What now?

For the real solution, you need some imagination. Some people see it at once; others see it after faltering through unsuccessful attempts; and others fail to solve it at all without some outside help. Here's the answer: take the tacks out of the box. Tack the box to the wall. Light the candle. Soften the bottom of the candle with a match, so that the wax begins to drip into the box, and place it inside the box. Run out of the room before the candle burns low enough to set the box on fire. Voilà.

Why don't so many people see that alternative right away? They, like Gregory or Lestrade, go at once for the most natural or most obvious solutions. Tacks? Surely you must tack the candle. Or, wax melts, so why not use it to stick the candle directly to the wall (that's slightly more creative, I grant)? The majority of people in this situation do not see that something obvious--a box of tacks--might actually be something less obvious: a box and tacks.

It's what's known as functional fixedness. We tend to see objects the way they are presented, as serving a specific function that is already assigned. The box and tacks go together as a box of tacks. The box holds the tacks; it does not have another function. To go past that and actually break the object into two component parts--Ah, I don't have three objects, I actually have four to work with--takes an imaginative leap (note that Duncker came from the Gestalt school and so was studying precisely this question, of our tendency to see the whole over the parts).

Indeed, in follow-ups to Duncker's original study, one experiment showed that if the objects were presented separately, with the tacks sitting beside the box, the percentage of people who solved the problem rose dramatically. Ditto with a simple linguistic tweak (and that's a lesson for another time: the importance of the language we use to think in how we actually do think): if participants were primed, prior to encountering the candle problem, with a series of words connected with "and" instead of "of," as in a box and tacks, they were much more likely to see the solution. And, even if the words were just underlined separately, as five items (candle, book of matches, and box of tacks), participants were also much more likely to solve the problem.

It's in the absence of those external nudges in the right direction of thought that people can get lost. Then, they have to provide the nudges on their own - and it is here that imagination is required (note a similar effect in the famous pendulum problem: without a push, the solution remains out of reach for many, but given the right prime…).

Imagination is often the mother of truth

Imagination allows us to see things that aren't so, be it an escaped horse that we never saw escape, a tyrant hiding just beyond the reach of the law, or a box of tacks that can also be a simple box. In other words, it lets us see what might have been and what might be even in the absence of firm evidence. When all of the details are in front of you, how do you arrange them? How do you know which are important? Logic gets you part of the way; imagination, the rest.

Holmes gets to the very heart of the matter in "The Valley of Fear," when he admonishes Watson that, "there should be no combination of events for which the wit of man cannot conceive an explanation. Simply as a mental exercise, without any assertion that it is true, let me indicate a possible line of thought. It is, I admit, mere imagination; but how often is imagination the mother of truth?" Therein lies its power.

[Photo credit: Inspector Lestrade arresting a suspect. From the Sherlock Holmes story "The Cardboard Box." Original caption was, "He held out his hands quietly." By Sidney Paget (1860-1908) (Strand Magazine) [Public domain], via Wikimedia Commons]

Previously in this series:

Don’t Just See, Observe: What Sherlock Holmes Can Teach Us About Mindful Decisions

Lessons from Sherlock Holmes: Paying Attention to What Isn’t There

Lessons from Sherlock Holmes: Cultivate What You Know to Optimize How You Decide

Lessons from Sherlock Holmes: Perspective Is Everything, Details Alone Are Nothing