Anyone who lives in a city is accustomed to seeing other people—usually lots of them. Remarkably, Edward Hopper lived and worked in New York and painted moments in which the settings are sparsely populated, if at all. And the people in his images are often absorbed in an inner world. They’re both part of and apart from the scene in which we see them.

A quick visit to the current New York exhibition of Hopper’s work attuned me to such moments. Now, it occurs to me, that’s what most of us h...