Corridors is very simple and not very important to performing improv, but it’s a pet peeve of mine seeing people getting it wrong. As far as I’m aware, there isn’t a guide anywhere online for how to do corridors correctly, so let this be the definitive guide.
Once a group of improvisers knows how to do corridors, it makes it incredibly easy to do scenes in pairs. The most common use case is to quickly run though a bunch of scene-starts to warm up for a show or a rehearsal. When done correctly, corridors guarantees that everyone gets an equal amount of stage time without repeating the same pair twice. Here’s how I set it up for a new group:
Get into two uneven lines on either side of the stage.
The two people in the front of each line will do a scene.
When I call scene, both people will go to the back of the opposite line they came from.
Keep in mind which players were in the first scene. When they are in front again, everyone will have done exactly two scenes. As long as the lines are different lengths, everyone will have played with two different scene partners.
Variant 1: If everyone is just doing two scenes, you can tell them, “sit down after you’ve done two scenes.” The lines will magically even themselves out, and people don’t have to stand longer than they need to.
Variant 2: If you would like people to do more than two scenes, after everyone has done two scenes and everyone is back to their starting position, tell the person at the front of the shorter line to move to the back of the longer line. After this one shift, you can go through the corridors again like normal, and everyone will magically have two new scene partners. You can repeat this until there are no players remaining in the shorter line.
Which is the front of the line?
I’ve heard arguments for both the upstage side and the downstage side, but I am partial to making the front of the line on the upstage side. This forces players to make the conscious decision to play downstage, which students always struggle with. It might make more sense to flip it depending on the room you’re in though.
How do people get it wrong?
Most of the time, it’s people trying to rearrange themselves to vary up their scene partners. Inevitably this leads to people getting confused. Instead, if you’re following the rules, just trust in the magic of the corridors.
Explaining the Magic (warning: math)
You don’t need to know why corridors works out, as long as you remember the steps. Nevertheless, for the curious, this is why it works the way it does. If you follow the path the players take across the stage, it makes a figure eight pattern—essentially, a loop with a twist in it. Let’s number the players in the loop from 1 to p following the loop. Suppose there are s players in the shorter line. Then, in one loop through, the nth player will do scenes with the (n-s)th player and the (n+s)th player (looping back around if the numbers go below 1 or above p). As long as the lines are uneven, n-s and n+s are different numbers. The move explained in variant 2 keeps the loop intact but decreases s by 1. It is possible for s to be zero, but then people will be in scenes back to back.
Fun fact: With an odd number of people, if you start with the lines as close to even as possible, following variant 2 will eventually have every player do one (and exactly one) scene with each other person. With an even number of people, this is possible too, but it becomes a little more complex, so I’ll leave it as an exercise for the reader.