THE 300th birthday of Jean-Jacques Rousseau falls next week, and it is only proper to wish him a happy one. He had a few choice words to offer on the theme of happiness — the sort associated not with fleeting social pleasures but with “nothing external to ourselves, nothing if not ourselves and our own existence.”

In 2010, two Harvard psychologists, Matthew Killingsworth and Daniel Gilbert, performed a study that used an iPhone app to ask volunteers, at random moments, what they were doing and how happy they were. They discovered that we spend most of our lives not thinking about what we are doing at that moment, whether it’s shopping, eating or, in particular, working. No matter how enjoyable or unenjoyable the activity we’re engaged in is, this gift for distraction comes at a psychic cost: “a wandering mind,” they wrote in the journal Science, “is an unhappy mind.”

No one seemed to remark on the incongruity of scientists’ using a technology that, in studying their subjects’ inability to focus, interrupted their focus.

The paradox would not have been lost on Rousseau, who believed we were happy only in our original state of nature — before the advent of technology and society. It was not that our thoughts did not yet wander but rather that there simply were no thoughts, wandering or otherwise, knocking about inside our heads. Our soul, “agitated by nothing,” gave itself up entirely to “the sentiment of its present existence without any idea of the future.” Our first ancestors stood Descartes’s axiom on its head: I don’t think, thus I truly am.