Where Did “Thirty Days Has September …” Come From? Just about every elementary schooler learns the months of the year with an easy rhyme: “Thirty days has [or hath] September, April, June, and November. All the rest have 31, except February …” How exactly does it end? That depends on how you learned the poem, but the first lines continue to help us remember the idiosyncrasies of our calendar. (Rhymes or phrases that help you remember something are called mnemonics, named after the Greek goddess of memory, Mnemosyne.) Origin story This mnemonic helps us keep our months and days straight. But, where did it come from? The rhyme has been attributed to many different sources, including Mother Goose, but a Welsh scholar may have uncovered its earliest source. He claims that the poem actually dates back to 1425. However, the words have changed slightly. Originally, the poem read: “Thirty days hath November, April, June and September …” Since November and September rhyme and they have the same number of syllables, they can easily switch places in the poem. The usefulness of the rhyme continues even as its internal linguistic conventions change. We’d never say “hath” nowadays, so the poem has evolved to reflect our current variation of hath: has. Counting on the calendar This poem also obviously relies on the calendar staying the same. We’ve been using the Gregorian calendar (and its similar predecessor, the Julian calendar) for quite some time. Recently, though, an economist and an astrophysicist at Johns Hopkins University developed a new calendar that would not require a leap year and would make dates occur on the same day every year. They still have to think of a new rhyme. Can you think of other useful mnemonic devices that rely on rhyme and word play?