“I’ll take the weather machine,” you say to him.

“Okay,” says Chet. “I’ll have it delivered first thing in the morning.

* * *

The next morning, there is a large package waiting for you. You open it to reveal your new weather machine. It has a few dings and scratches on it, but it still looks completely functional. You start to imagine all the things you could use it for.

You could create hurricanes and blow people miles away from their homes. You could create droughts until people are dying for water, and then drown them all with monsoons.

You examine the controls for the weather machine. They appear to consist of nothing but a single dial. The dial has two settings: “hot” and “cold.” No wonder you got it so cheap.

• Do you want to bring on the heat?
• Do you want to bring on the absence of heat?