The numbers that surprise learners
French counts regularly up to sixty: trente, quarante, cinquante, soixante. Then the pattern changes. Seventy is “soixante-dix”, sixty-ten. Eighty is “quatre-vingts”, four twenties. Ninety is “quatre-vingt-dix”, four twenties and ten. A number like 99 is “quatre-vingt-dix-neuf”, four twenties, ten and nine.
The arithmetic works in a way that is easy to check: 4 x 20 = 80, and 80 + 10 + 9 = 99. The puzzle is why a language descended from Latin, which counted in tens, has a strand of counting in twenties.
Belgium, Switzerland and elsewhere
Not every French speaker uses these forms. In Belgium, speakers use “septante” for 70 and “nonante” for 90, which are regular tens: seven tens and nine tens. Belgian French still says “quatre-vingts” for 80, so the system there is mixed. In French-speaking Switzerland, “septante” and “nonante” are also standard, and for 80 several cantons say “huitante”, while others, including Geneva, use “quatre-vingts”. “Octante” is an older form that is sometimes reported in regional use. The Aosta Valley in Italy is also reported to use forms of this kind in its French.
So the forms that look unusual in Paris are not universal. The regular series, based on Latin “septuaginta”, “octoginta” and “nonaginta”, is old and was once used in France too. Medieval French texts include forms such as “septante” and “nonante”, and the shift to the twenties-based forms happened over time. In the seventeenth century, grammarians in France discussed which forms to prefer, and the vingt-based forms became standard in Paris. That is a general outline, and the exact dating differs between sources.
The vigesimal element
A system that counts in twenties is called vigesimal. In French it is limited to the numbers from 60 or so to 99, and some older forms went further. Medieval French used expressions like “six-vingts” for 120 and “quinze-vingts” for 300, meaning six twenties and fifteen twenties. The best-known survival is the “Quinze-Vingts” hospital in Paris, founded in the thirteenth century and traditionally described as housing 300 blind residents, fifteen twenties. The name stuck long after the counting form fell out of ordinary use.
Where did the twenties come from? There are several proposals, and none is certain.
- One is a Celtic origin. Gaulish, the Celtic language spoken in Roman Gaul before Latin took over, may have counted partly in twenties, in the way that Welsh and Irish had vigesimal elements. A Celtic influence on French is an appealing idea, though evidence for the details of Gaulish numerals is thin.
- Another is Norse influence. Scandinavian settlers, from whom the Normans partly descended, arrived in northern France in the tenth century, and Danish today uses counting in twenties for some tens. A Norse source is sometimes proposed to explain why the forms are especially associated with northern French.
- A third view is that it was a combination, or a development within French itself, helped by the practical convenience of counting goods in twenties.
Scholars still discuss all of these. It is more honest to say that the origin is uncertain than to name one cause as proven.
Similar systems elsewhere
French is not alone. Danish counts 60 as “tres”, short for three twenties, and 80 as “firs”, four twenties, and its 50 is “halvtreds”, an older expression meaning half-way to the third twenty. Welsh has traditional counting with twenties alongside a newer decimal system, and Irish has older vigesimal forms as well. Basque and Georgian are non-Indo-European languages known for counting in twenties, an arrangement known as base twenty counting.
English keeps a trace in the word “score”. “Four score and seven” means 87, and the phrase is a reminder that older English once counted in twenties, a habit that survives among the traditional counting units. The reason such systems arise is unclear, though the ten fingers and ten toes have long been suggested. Compare the idea behind body counting systems, where parts of the body serve as a counting scale. As always, such links are suggestions and not documented causes.
How the written forms work
A few rules help with reading the written numbers. In “quatre-vingts” the final “s” appears when nothing follows, so that 80 is “quatre-vingts” while 81 is “quatre-vingt-un” without the “s”. Since a spelling reform in 1990, hyphens are recommended throughout compound numbers, though older forms without them are still seen. In France, 71 is “soixante et onze”, with “et”, while 81 is “quatre-vingt-un”, without it, which is one of the small irregularities learners have to memorise.
Why the forms persist
Standard French in France has kept the vigesimal forms for several centuries, and there is no sign that they will be replaced. Education, publishing and national norms reinforce them. In Belgium and Switzerland, on the other hand, the regular forms remain in use alongside the national standard, which means that two systems coexist inside one language. Speakers usually understand both.
The case shows how a number system can differ even between regions that share a written language, and how little the surface of a language tells you about its arithmetic. French is a Latin-descended language that counts partly like a Celtic or Scandinavian one. Whether that is a trace of other languages or a development of its own, the system is a good example of the way number words change over time.