We Live By a Unit of Time That Doesn’t Make Sense

Days, months, and years all make sense as units of time—they match up, at least roughly, with the revolutions of Earth, the moon, and the sun.

Weeks, however, are much weirder and clunkier. A duration of seven days doesn’t align with any natural cycles or fit cleanly into months or years. And though the week has been deeply significant to Jews, Christians, and Muslims for centuries, people in many parts of the world happily made do without it, or any other cycles of a similar length, until roughly 150 years ago.

Now the seven-day week is a global standard—and has come to dominate our sense of where we stand in the flow of time, according to David Henkin, a historian at UC Berkeley. His new book, , traces the evolution—and analyzes the curious staying power—of what he lovingly refers to as