The day that's in it

Today is Friday 13th.

As to why this day should be considered unlucky, Melancholicus heard an explanation from a friend of his some years ago—namely Alaisdir Ua Seaghdha—a gentleman of wide reading and intellectual acumen. This explanation does not occur on the Wikipedia page for Friday 13th, so it bears some repeating here.

If any of these orally recounted details should be faultily remembered, perhaps Alaisdir could post a correction.

The association of Friday 13th with ill-luck began after the Reformation. Prior to this great religious upheaval, Friday 13th was not considered unlucky at all—in fact quite the opposite. This was a particularly lucky day, indeed an auspicious day, since it combined two elements associated with good fortune: the sixth day of the week, and the number thirteen.

In the Middle Ages, thirteen was a lucky number since this represented the number of people present in the upper room at the Last Supper—Christ and His Apostles.

The sixth day of the week—Friday—was considered a lucky day, since this is the day on which the Redemption occurred.

So a day on which these two fell together was regarded as an exceptionally lucky day.

But after the Reformation, with the rejection of all things popish and the rejection likewise of what were considered “popish superstitions”, the association of Friday 13th with good luck came to an end. So eager were the Reformers to retreat from such superstitions that they created an alternative superstition of their own—that Friday 13th instead of being an auspicious day was rather a day of calamity and misfortune.

Owing to the dominance of Protestantism, at least in the English-speaking world, so it has remained ever since.