Beliefs, not facts about numbers
Nothing in a number makes it lucky or unlucky. What can be documented is that people in particular societies have treated certain numbers as welcome or as ill-omened, and that these habits leave visible traces: missing floors in buildings, premium prices for certain phone numbers, proverbs, and dates that people avoid for weddings or journeys. This article surveys some of those traces. It describes beliefs that people held, and in many cases still hold, without suggesting that the beliefs predict anything.
Two cautions apply throughout. First, a country is not a single mind; within any society some people take a superstition seriously, some treat it as a joke, and many have never heard of it. Second, the explanations attached to these customs are often later stories. Where the evidence is thin, it helps to say so.
Sound and spelling
The most reliably documented reasons for number preferences are linguistic. When a number word sounds like another word, the number can inherit that word’s associations.
In Mandarin Chinese, the word for four, sì, is close in sound to the word for death, sǐ, differing mainly in tone. Similar sound-alikes are reported for the Japanese and Korean readings of four, which is why four is sometimes left out of floor and room numbering in those countries, a pattern discussed under tetraphobia in East Asia. The Japanese reading ku for nine is also said to resemble a word for suffering, so nine is sometimes avoided too.
Eight works in the opposite direction. The Chinese word for eight, bā, sounds like fā, a word associated with getting rich or prospering, and the link is especially close in Cantonese. This is part of the wider set of Chinese number homophones that people read into digits, and it is a main reason eight is linked with eight and prosperity in popular belief. The Beijing Olympic Games opened on 8 August 2008 at 8:08 in the evening, a date and time widely understood to have been chosen with this in mind. The same logic explains the high prices sometimes paid for auspicious phone numbers and vehicle plates containing eights.
Thailand offers another sound-based favourite. The Thai word for nine is pronounced much like a word meaning to step forward, so nine is generally welcomed. That case is covered in its own article.
Memory, religion and history
Not all taboos are about sound. The best-known Western example, thirteen, is usually explained by stories rather than by language. Popular accounts point to a thirteenth guest at a meal bringing trouble, with the Last Supper and a Norse banquet story as common examples, but how far these stories explain the habit is uncertain. The wider folklore around unlucky thirteen is a topic in its own right. What can be observed today is the practical result: many buildings label floors so that no floor is numbered thirteen, and some airlines leave out a row thirteen. The floor itself still exists; only the label changes.
Italy has a different taboo, aimed at seventeen. The usual explanation is that the Roman numeral XVII can be rearranged into VIXI, Latin for “I have lived”, a phrase that implies “I am dead”. The anagram works only in Roman numerals, a reminder of how numeral writing can shape a superstition. Italy is also a case where thirteen is not feared in the same way. The Italian phrase “fare tredici” is commonly used for a big success, and it is usually linked to football pools that once asked players to predict thirteen results.
Days and dates
Some taboos attach to a day of the week or a date rather than to a bare number. In English-speaking countries the combination is Friday the 13th. In Greek and Spanish tradition, the unlucky day is instead Tuesday. A Spanish proverb advises neither marrying nor setting out on a journey on a Tuesday, and Greek tradition remembers a Tuesday as the day Constantinople fell in 1453. The day names in these traditions come from the seven-day week, which in many European languages is built on planetary and divine names, and that helps explain why weekday superstitions differ from place to place.
Favourites that come from pattern
Some lucky numbers seem to come from habits of counting and speech rather than from words that sound alike. Seven is a favourite in English, where “lucky seven” is a stock phrase. Seven in antiquity was already prominent, since many ancient cultures counted seven planets or days, though that history differs from the later English saying. Three is a favourite in storytelling: tales and speeches tend to arrive in threes, which folklorists have discussed as a pattern of narrative economy. Odd numbers were praised by Roman writers, including a famous line in Virgil, and they had a prior history in Pythagorean number philosophy.
In Turkish and Middle Eastern folk custom, the number forty marks periods after a birth or a death, and it also appears in sayings. In English, counting rhymes and nursery rhymes carry numbers that children learn long before they know any belief attached to them, even though some modern writers claim hidden meanings in them.
Why these beliefs persist
Researchers who study superstitions often note that such customs are cheap to follow. Skipping a floor label or avoiding a date costs little, and the habit passes easily from person to person. Business owners may also follow a custom because customers expect it, whatever the owners themselves believe. Numbers that look the same across languages can carry different meanings: four is feared in some East Asian settings and not in others, nine is welcomed in Thailand but is sometimes avoided in Japan, and thirteen is avoided in much of the English-speaking world but is treated as a sign of success in Italian football-pool slang.
For the reader, the useful lesson is how much of “luck” turns out to be language, calendar and history. A claim that a given number is lucky everywhere or unlucky everywhere is almost always a simplification. The more careful statement is narrower: in this place, in this period, people attached this meaning to this number, for reasons that can sometimes be traced and sometimes cannot.