Today’s Sunday Rerun takes up the question: What would Marshall McLuhan make of the smartphone? I wrote this in 2014, when the smartphone had displaced the laptop and desktop as our personal computer of choice but had not yet become our heart’s desire.

The lightbulb, Marshall McLuhan wrote at the start of his 1964 book Understanding Media, is an example of a medium without content. Walk into a dark room and hit the light switch, ...