Why Does French Count in Twenties?
The Celtic and Medieval Origin of Vigesimal Counting
Updated 17 April 2026
If you have ever tried to learn French numbers, you have hit the wall at 69. Seventy is not "septante" as logic would suggest - it is "soixante-dix" (sixty-ten). Eighty is not "octante" but "quatre-vingts" (four-twenties). Ninety is "quatre-vingt-dix" (four-twenties-ten). You are doing arithmetic. Why?
The answer involves Celtic counting traditions, Roman conquest, medieval French, and a 19th-century standardisation argument that Belgium and Switzerland decided to ignore. The story is genuinely interesting.
The Celtic Base-20 Origin
The Gauls, Celtic tribes who inhabited what is now France before Roman conquest (around 50 BCE), used a vigesimal counting system - base-20 instead of base-10. Evidence for this comes from linguistic archaeology: the word for 80 in several Celtic languages means "four-twenties", not "eighty". Welsh still uses this today: "pedwar ugain" for 80.
Why base-20? Anthropologists suggest that early counting used both fingers and toes as counting aids. A base-20 system counts from 0 to 19 using all digits, then starts a new group. Base-10 (our standard) uses only fingers. Base-20 is found in several unrelated languages and cultures, suggesting it arose independently from the same physical constraint.
The Basques (in southern France and northern Spain) also use a vigesimal system, which predates both Celtic and Roman influence in the region, suggesting vigesimal counting was ancient and widespread in pre-Indo-European Europe.
Latin Arrives, But Doesn't Fully Displace Celtic
When Julius Caesar conquered Gaul between 58-50 BCE, Latin became the language of administration, commerce, and eventually daily life. Latin is a base-10 language: decem (10), viginti (20), triginta (30), quadraginta (40), quinquaginta (50), sexaginta (60), septuaginta (70), octoginta (80), nonaginta (90). These forms gave rise to septante, octante, nonante in some Romance languages.
Old French, which developed from Vulgar Latin between roughly 600-1100 CE, had both base-10 forms (septante, octante, nonante) and base-20 forms (quatre-vingts etc.) in use simultaneously. Medieval French texts show both systems. The base-20 forms appear to have been particularly persistent in the speech of the Frankish nobility and in northern France.
There is a hypothesis that the Celtic-influenced nobles who adopted Latin counted in twenties as a prestige marker - a way of distinguishing their speech from common Latin. Whether true or folk etymology, the base-20 forms survived and eventually dominated in French.
The 19th Century Standardisation and the Belgian/Swiss Divergence
By the 18th century, France had both systems in written use. Moliere used quatre-vingts. The Academie francaise, founded in 1635, had begun advocating for linguistic consistency. In the Revolutionary and Napoleonic periods, France undertook a massive standardisation of language to create a unified national identity. The vigesimal forms were chosen, perhaps because they appeared in more prestigious literary texts, perhaps because reforming them would have required changing too much existing material.
Belgium achieved independence in 1830. Switzerland had been a confederation since 1291. Neither country was subject to French standardisation edicts. Their populations continued using the forms they had grown up with - septante and nonante for 70 and 90. Switzerland's huitante and octante forms for 80 exist in specific cantons; Belgium kept quatre-vingts for 80, matching France, but diverged at 70 and 90.
The irony: Belgium and Switzerland ended up with the more Latin-derived, "logical" forms, while France retained the Celtic-influenced vigesimal ones. If the Academie francaise had chosen differently in the 19th century, French could have had septante, octante, nonante like its neighbours. The decision that locked in soixante-dix and quatre-vingts as standard was essentially political, not linguistic.
Vigesimal Systems Around the World
French is not alone. Other languages have vigesimal remnants or complete vigesimal systems:
Welsh
Extensive vigesimal system. 15 = pymtheg (five-ten), 50 = hanner cant (half-hundred), 70 = deg a thrigain (ten and sixty), 80 = pedwar ugain (four-twenties).
Danish
Uses halvtreds (50), tres (60), halvfjerds (70), firs (80), halvfems (90) - remnants of a vigesimal system. 70 = halvfjerds = "three-and-a-half twenties".
Basque
Fully vigesimal. 40 = berrogei (two-twenties), 60 = hirurogei (three-twenties), 80 = laurogei (four-twenties). Predates Celtic and Roman influence.
Georgian
Uses vigesimal counting above 20. 40 = ormoci (two-twenties), 60 = samoci (three-twenties), 80 = otxmoci (four-twenties).
Maya numerals
The Maya used a base-20 positional system for mathematics and astronomy - the most sophisticated vigesimal system in the ancient world.
The Modern Learner's Burden
This history explains why French numbers above 69 feel harder than Spanish, Italian, or German numbers. Spanish setenta (70), ochenta (80), noventa (90) are straightforward descendants of Latin. French's soixante-dix, quatre-vingts, quatre-vingt-dix require active decomposition and arithmetic.
For language learners, the key is accepting that this is not a quirk but a feature. French is doing arithmetic that other languages eliminated. Once you make peace with that and memorise the three patterns (soixante + teens, quatre-vingt + units, quatre-vingt + teens), the system becomes navigable. It never becomes as automatic as base-10, but it becomes manageable.
The drill on the 70-99 page is designed specifically to build the automaticity you need. Fifty successful recalls of each number is a reasonable target before they start to feel natural.