Why is the number 13 considered unlucky?
Currently 13 is considered to be an unlucky number. However, I am told it used to be — and in some earth-worshipping, i.e., pagan, religions still is — a lucky and magical number. Consequently there were 13 months and 13 zodiac signs (the Gemini twins had separate identities). Knowing how Christianity and other god-as-a-man-based religions were prone to say that what the pagans (Earth-and-god-as-a-woman) considered good was bad, I wonder if this was the case with the number 13. And why was 13 singled out of an infinity of numbers in the first place? Also, if the number 13 is so bad, why is it reflected so many times on the U.S. $1 bill — 13 levels in the pyramid, 13 stars, 13 arrows, 13 stripes, 13 leaves, and 13 olives? Is it because of the original 13 colonies?
Thirteen stripes, 13 colonies … nah, it's just coincidence. The matter of how 13 came to be a numerological pariah, on the other hand, is an interesting story. While your rap about the pagans is a little off the wall (Thor the feminist?), you're right about one thing: 13 hasn't always been considered unlucky.
Though I wasn't able to do as thorough a study of crosscultural number significance as I would have liked — the Straight Dope Field Survey Team preferred to be read to from The Cat in the Hat — what I've seen suggests that in ancient times 13 either was considered in a positive light or, more commonly, wasn't considered at all. I note, for example, that the Gnostics of the early Christian era totted up 13 Conformations of the Holy Beard. The significance of the Holy Beard is not entirely clear to me, but I gather it's something you wanted on your side. Thirteen was also once associated with the Epiphany by mainstream Christians, the Christ child having received the Magi on his thirteenth day of life.
But 13's stock dropped like a rock in the middle ages. The proximate cause of this apparently was the observation that Judas, the betrayer of Jesus, made 13 at the table. Other great medieval minds, I read here, pointed out that "the Jews murmured 13 times against God in the exodus from Egypt, that the thirteenth psalm concerns wickedness and corruption, that the circumcision of Israel occurred in the thirteenth year," and so on.
Pretty thin excuse for maligning a number that never meant any harm, you may think. I agree. We must inquire further, and if we do we conclude that while open hostility to 13 may be relatively recent, folks have had their suspicions about it for quite a while. Thirteen is a prime; primes have always attracted attention (compare 7). What's worse, 13 is one past 12, the dozen, almost universally regarded as a perfect number, signifying harmony and all good things. Thirteen, by contrast, is a number of transgression, taking matters one step too far, turning harmony into discord.
A bit of a stretch? Maybe. But consider how often 13s seem to intrude on our tidy arrangements of 12. In many a twelvemonth, to use an old term, there are 13 full moons, and a woman on a 28-day menstrual cycle will be "unclean," as Leviticus has it, 13 times a year. The moon has long been a female symbol, and the full moon, (male) chroniclers tell us, is when (female) witches fly. I hesitate on that evidence alone to ascribe triskaidekaphobia to the fell hand of the patriarchy. But 13's bad reputation may have more to do with fear of women, witchcraft, and disorder than is commonly supposed.