This is part of a very old tradition of divination based on natural phenomena - and in particular based on numbers found in nature. The focus on a magpie may reflect early divine aspects of the bird. Some see in name as originally “Morgana’s Pie,” a reference to a powerful female deity who was the basis of the Arthurian character Morgan le Fey, but that etymology is not universally accepted.

Originally there were many variants of the rhyme, although they all tended to hang together with regard to basic approach. The following are two excerpts from my Introduction to Folklore addressing the magpie rhyme in particular and the use of numbers and divination in general:

Many people regard various natural phenomena as indicators of future events. The flight of birds, the internal organs of animals, the appearance of the new moon at the beginning of a season, the movement of smoke from a fire, or any number of other things could be used to predict the future. The Roman science of augury took this form of divination to an extreme, but the folk have always sought signs from nature to indicate the future.

Interpretations of events in the world are often opportunistic in that someone divining the future may see significance in odd occurrences, without particular significance identified in the local folklore. Other subjects of divination are clearly defined by oral tradition. The Irish and some places in Britain, for example, regard the number of magpies first seen in the morning as an indication of how the day will proceed. The Irish have a rhyme, which has been recorded with several variations, that recites the possibilities: “one for sorrow, two for joy,” and so on for indications of everything from luck to poor business dealings. Cornish-born historian A. L. Rowse (1903-1997) recorded the rhyme as “one for sorrow, two for mirth; three for a wedding, four for a birth.”

And a second excerpt:

The ancient idea that Yule is the time for predicting the future is behind the notion of the song “The Twelve Days of Christmas.” Modern Americans often misunderstand the twelve days of Christmas, frequently regarding them as the last shopping days before the holiday. In fact, they are the days that begin with Christmas and end on January 6, Epiphany. According to tradition, this was the period that spanned the birth of Jesus and the adoration of the Magi. In America, the twelve days have shifted from a time of celebration to one of preparation. Christmas Day serves as the climax rather than the beginning. Even the wise men now appear on Christmas Eve in most American traditions.

The song “The Twelve Days of Christmas” has meaning now lost to most people. For example, the number of gifts the song describes is no accident. There is, of course, only one gift – the partridge in a pear tree – on the first day, but as anyone knows who has sung the song, the number of gifts quickly escalates. Thus, there are three gifts on the second day – two turtledoves and yet another partridge. There are six gifts on the third day and so forth until seventy-eight gifts appear on the twelfth day. The gifts from all the days total 364, one for each day of the year (minus one).

This is more than a clever trick placed subtly in the carol. European folk culture traditionally viewed the twelve days of Christmas as the time when one could predict the future. Each day represents one of the months of the coming year. By watching the weather or performing magic on any given day, one was able to forecast the nature of the corresponding month in the following year. The number of gifts in “The Twelve Days of Christmas” apparently draws on the belief that the Christmas season magically reflects the following year.

Yet another tradition surrounding this carol is the role it once occupied as a game. As an Irish farmer from County Clare told a folktale collector in 1940, one child hands another a bucket of turf asking “What’s that?” The recipient then answers, “Two ducks and a fat hen,” passing it back with the same question, which is answered with an additional three items. The first one to fail reciting the items in order loses. This sort of game appears to be behind the carol “The Twelve Days of Christmas,” which retains a humorous quality.