Common sense has been called the “dark matter of AI”—both essential and frustratingly elusive. That’s because common sense consists of implicit information—the broad (and broadly shared) set of unwritten assumptions and rules of thumb that humans automatically use to make sense of the world. For example, consider the following scenario:

A man went to a restaurant. He ordered a steak. He left a big tip.

If you were asked what he ate, the answer—steak—comes effortlessly. But nowhere in that little scene is it ever stated that the man actually ate anything. When Ray Mooney, the director of the Artificial Intelligence Laboratory at the University of Texas at Austin, pointed this out after giving me the same pop quiz, I didn’t believe him at first. “People don’t even realize that they’re doing this,” he said. Common sense lets us read between the lines; we don’t need to be explicitly told that food is typically eaten in restaurants after people order and before they leave a tip.

Computers do.