70, 80, 90 – quirks of the French language
Have you ever wondered why the French say “soixante-dix” (sixty-ten), “quatre-vingts” (four-twenties), and “quatre-vingt-dix” (four-twenties-ten) rather than simpler forms which would conform with the decimal system (like seventy, eighty and ninety) ?
This can be quite confusing for those who are new to numbers in French, particularly when someone is giving you a phone number like this one !
The modern French versions of the numbers 80 and 90 are actually relics from the Middle Ages, when France used a number system based on 20 rather than 10. With this system, once they were past twenty they used to say twenty-ten (30), two twenties (40), two twenties ten (50), three twenties (60) and so on, even going beyond a hundred. Saint Louis founded, for example, the “Hospice of the Quinze-Vingts” (of the 300). This system, known as “vicesimal,” was used by the Celts and the Normans, and it is likely that one or the other of these introduced it into ancient Gaul, geographically modern France.
By the end of the Middle Ages, however, the modern number forms of trente (30), quarante (40), cinquante (50) and soixante (60) came into common usage. Decimal forms of septante, octante, nonante also came into being for 70, 80 and 90 , but they were not commonly adopted. Why did the strange old forms for 80 and 90 persist, and a weird hybrid “soixante-dix” for 70? There’s no definite explanation – it’s French, after all!
What we do know is that it was in the seventeenth century, under the influence of Vaugelas and Ménage, that the Académie Française (guardians of the official French language) and authors of other dictionaries adopted the forms soixante-dix, quatre-vingts, quatre-vingt-dix for 70, 80 and 90 instead of the more “modern” introductions septante, octante, nonante. It should be noted, however, that the words septante, octante, nonante DO still appear in the Dictionnaire de l’Académie Française, the official French dictionary. Furthermore, these decimal versions are recommended in the teaching of maths and they even remain in spoken use in parts of the East and the Midi of France, as well as in Acadia. They are also official in Belgium and Switzerland (except for “octante” in Switzerland which has been supplanted by “quatre-vingts” and “huitante”). Nothing prohibits the peculiar “French” versions from being used in Belgium and Switzerland but they are perceived there as regional or antiquated, in contrast to their common usage in France.