What makes a Christmas song Christmassy?

Temperature records for Los Angeles in the summer of 1945 are patchy, but 90 in the shade seems to have been the norm. It was during one such scorcher, presumably, that the songwriters Jule Styne and Sammy Cahn pulled up at a red light on the corner of Hollywood and Vine. Cahn suggested going to the beach. Styne had a better idea: ‘Let’s go write a winter song.’ Driving over to the offices of their publisher Edwin H. Morris, Cahn commandeered a typewriter, glanced out the window and typed the exact opposite of what he saw: ‘The weather outside is frightful.’ The Great American Songbook had acquired another Christmas classic.

And ‘Let it Snow!’ is no less classic – and all the more American – for omitting any mention of Christmas. That wasn’t obligatory (Mel Tormé’s ‘The Christmas Song’ was born in the same Californian heatwave). But in a melting-pot America, it made commercial sense. Many of the seasonal standards created during that glorious mid-century harvest of melody don’t mention Christmas at all – ‘Winter Wonderland’, ‘Jingle Bells’ – or, if they do, it’s a distinctly secular version: ‘White Christmas’, ‘Rudolph the Red-nosed Reindeer’. Authentically religious Christmas songs have had a chequered history since the baby boom, though rarely as bizarre as the 1976 Johnny Mathis hit ‘When a Child is Born’ – a melody that had previously featured in the Argentinean werewolf movie Nazareno Cruz and the Wolf (‘The doves, and the screams!’).

The less specific you can be, the broader the scope for royalties. The question, then, is what – in musical terms – constitutes an irreducible minimum of Christmas-ness? Leroy Anderson cracked it back in 1946. ‘Sleigh Ride’ was conceived (you guessed it) in a heatwave – the catchiest in a long series of impossibly tuneful encores that Anderson composed for the Boston Pops Orchestra.