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How to Think Like Sherlock Holmes: Deduction from the Facts, with Maria Konnikova, psychologist
For Holmes, deduction doesn’t mean deduction in the formal logic sense. So when we use deduction in the Holmesian sense, all it means is, let’s take the information that we have and let’s see where this information leads us. So, what can we do given everything that we’ve observed, given everything that we’ve seen, given everything that we’ve played around with in the brain attic? What does that tell us? For Holmes, this means going through different possibilities and eliminating them one by one until you are left with the possibility that is the one that is most likely to be true.
Deduction seems to be the easiest part of the process because you’ve already done all the hard work. You’ve already observed, you’ve already put in so much effort, so it’s seems like the problem should just be apparent at that time. But deduction is, in reality, very difficult because our minds like to deduce before we do.
One of the things that we’re very, very good at is telling ourselves stories. So we take information and we build narratives right away. We don’t even realize we’re doing it. We see something and right away we think, oh, I know how this got here; I know why it’s this particular object, I know what’s going to happen. You don’t realize you’ve told an entire story based on something you’ve seen. But your mind has already done that. And it’s incredibly difficult to realize that and then to take that story that you’ve told and separate it from the actual object and to say wait, wait, wait, for instance, all I’m seeing is a wine glass. I’m not seeing anything about that wine glass other than, there’s a glass of wine.
The reason I say wine glass is because wine glasses are used in one of the Holmes stories. Watson sees wine glasses and right away tells himself a story about how there were three people and two of them poured the remains of the third glass away. He has this entire narrative that has nothing to do with the physics of wine or with the reality of the evidence. But he tells himself that and to him that’s proof that there were three people in the room.
But what Holmes does is say, wait, wait a second; all we know is that there are three glasses of wine, but now let’s examine what is actually in the glass. Let’s step away from your narrative of three people, and so let’s see these just as wine glasses. And what he’s then able to tell is that only two of the glasses were used and the third glass just contains the remains that people put in, in order to try to make it look like there was a third person.
Counter the tendency to construct narratives by keeping track of the objective facts.
One of the things we can do to try to avoid this tendency to build narratives is to write things down, to try to create a list of what are the objectives facts. So what do I know? Let me sit down and let me write everything down. And then if I write it down, maybe I can see, maybe that will help me separate what is fact from what isn’t. So something that might have seemed like it was a fact in my head, might no longer be quite as factual once I put it on paper.
And if you don’t want to write it down, this is one of Watson’s essential functions for Sherlock Holmes. Holmes talks through everything to Watson because as he’s talking through it, logical flaws, these holes that wouldn’t be apparent were he to just think them, suddenly became clear because Watson questions him. Watson asks, well, why are you doing this? Why are you thinking this? Why are we going to go here? Why aren’t we going to go here? And Holmes must always explain. And so that helps catch the things that he wouldn’t catch otherwise. So in that sense, Watson is essential. And we can all have a Watson. You can always talk through something to someone else, or even to yourself, if no one else is available. People might think you’re a little bit crazy if they see you talking to yourself, but it’s a small price to pay for being able to think more clearly.
Distinguish between the improbable and the impossible.
Holmes often makes a distinction between the improbable and the impossible. In one story he says, “When you’ve eliminated the impossible, whatever remains, however improbable, must be the truth.” And what he means by that is that something that might seem incredibly unlikely, if you’ve eliminated all other possibilities, no matter how unlikely it is, you have to trust that it’s the right thing because if you trust your thought process and if you trust what got you to that final point, you can’t be afraid of going to that final point.
In Holmes’s case this sometimes takes very strange proportions. For instance, someone who people presumed was dead for the duration of the story is alive. And you seem to have the body, you seem to have the dead person; how in the world can a dead person be alive? If that’s the only remaining possibility, no matter how improbable it is, you have to accept it as being the possibility. And Holmes sometimes will discover that the person we thought was the dead person is really another dead person who happens to look a lot like him. Or maybe the person wasn’t dead at all.
We’re very scared of things that don’t seem like they’re likely. And it’s a bias that is pretty deeply ingrained in our minds. And so this particular mantra, I think, is important to keep repeating, that the improbable doesn’t mean that it’s impossible.