Plenty of today’s “Christmas carols” are unabashedly secular songs. So were many of the original Christmas carols, it’s just that their words were adapted to be overtly religious to celebrate Christian festivals. What we now call our sacred carols are typically festive, seasonal, and dancelike. Easter carols exist, but the most well-known sacred carols are for Christmas. The Christmas concert season often features other early music, too. Music that sounds “Christmassy” in part because our sacred carols are also largely early music.

The chaconne or passacaglia is one of these early-music tropes. There isn’t a fixed distinction between chaconne and passacaglia, or between these and other ground-bass forms (this is “ground” as in “foundational,” not as in we’re making sausage of the deep-voiced menfolk). But all describe a short bassline or chord progression repeated over and over … and over … again. The refrain of the carol “What Child Is This” (whose tune is also known as “Greensleeves,” and may or may not have originally been about a woman whose dress is green because she rolls around in the hay rather often), for example, uses a repeated romanesca progression. “What Child Is This” has a wistful, haunting character, and there’s no shortage of chaconnes in a minor key expressing lamentation (often with a bassline explicitly called a lament bass), but the chaconne seems to have descended from an impertinent, even “sexy” dance in 3/4 time.