How would a robot tax work? Gates mentions taxing both the robot owners — likely corporations — as well as some other sort of direct tax. One could imagine a sales tax, perhaps, or not allowing businesses to fully deduct the cost of certain advanced machines or software. European lawmakers just rejected taxing robots to pay for social insurance programs. But as Gates’ comments suggest, the idea seems likely to keep popping up, especially as technology penetrates ever deeper into our working lives.

Opponents argue that such levies would kill progress. But the end result of robot taxes might be less the end of automation than, as Gates said, to “slow down the speed of that adoption somewhat to figure out, okay, what about the communities where this has a particularly big impact?” It’s an idea that has a counterpart in the debate about trade. Economist David Autor, who has extensively researched the 21st century’s “China trade shock” on American blue-collar workers, recently told The Washington Post that if “we knew how disruptive this would be, we would have wanted to do it more slowly.”