Why

Chapter 8. Explanation

What does it mean to say that this caused that?

After a series of sleepwalking episodes, a man living in Kansas visited a sleep disorder clinic to find out what was wrong with him. A little over a month later, he was diagnosed with non-REM parasomnia, a sleep disorder that can lead to strange behaviors like walking or eating while asleep, with no memory of these incidents. Two months after the diagnosis, his medication dosage was increased, and two days later he was arrested and charged with killing his wife.¹

Accidental killings by parasomniacs are rare, but could this be one such instance? Some of the evidence suggested this could be so. Before the arrest the man made a 911 call where he spoke strangely and seemed confused about what had happened, making it seem that perhaps he was still asleep, given his history. On further examination, though, many of the features common to violence during sleepwalking were absent. He’d been arguing with his wife (but usually there’s no motive), he was not near her (proximity is usually necessary), and he used multiple weapons (when just one is more likely). Ultimately, it turned out to be a case of murder.

The key point is that just because parasomnia can cause murder and both parasomnia and murder were present here does not mean that the parasomnia must have caused this particular killing.

When we ask why something happened—why a riot started, why two people got into a fender bender, why a candidate won an election—we ...