Labyrinth

Prompt: Closed Doors

Today’s prompt got me thinking about all kinds of closed doors. I even asked Michael what he thought of when he imagined a closed door. He had some compelling ideas - doctors offices and airports and such. But as I pondered what to write, I kept coming back to a riddle that I saw on an episode of classic Who. It was an episode starring the Fourth Doctor, played by Tom Baker (the one with the scarf). The episode features a common riddle often called “knights and knaves” (or just “Two Doors, Two Guards”), in which the hero faces a particular puzzle that goes something like this:

The hero is trapped in a labyrinth. In order to escape, the hero faces two options; two identical closed doors, or sometimes two identical paths through the woods. One door (or path) leads to freedom, the other leads to death. With “The Pyramids of Mars” serial of Doctor Who, the Doctor’s companion is caught in a trap. There are two buttons; one button will release her, one button will kill her. But in each iteration of this scenario, there are also two guards - one who only speaks truth (the “knight”), and one who only speaks lies (the “knave”). In order to solve the puzzle, the hero may ask only one question in order to figure out which door/button/path to follow.

I admit, if I faced this scenario without already knowing the answer to the puzzle, I would spend an embarrassingly long time (days, weeks?!) pondering which door to open. The simple thing, to ask which door leads to freedom, would yield two different answers depending on which guard you asked. Asking which door leads to death would also result in a different answer from each. You don’t know which is telling the truth or lying.

[Pause here if you want to take a moment to figure out the riddle on your own.]

The solution to the riddle is to ask, “Which door would the other guard tell me leads to freedom?” The truthful guard would know that the other guard would lie, so he points to the door that leads to death. The lying guard would still lie and say that the truthful guard would also point to the door that lead to death. Now, regardless of which one answered your question, both the guards would point to the same door, and you can choose the opposite door, knowing it leads to freedom.

Even seeing them work through it in the episode, I had to pause and think for a while before I understood the puzzle. I saw that episode only once, so it must have made an impression to resurface when I faced a prompt about closed doors nearly ten years later.

Luckily, real life rarely has me facing life or death riddles. I don’t know the moral of this story, but I know that in real life, when faced with a problem, it never hurts to ask clarifying questions.