What counting in twenties means
A vigesimal system builds its number words around twenty, in the way a decimal one builds around ten. The usual explanation is the body: ten fingers and ten toes make twenty, so a person counting on every digit reaches twenty before starting again. This is a plausible origin, not a proven one. Languages do not record why their speakers chose a base, and many systems that use twenty also lean on ten and five, so they are mixed rather than purely vigesimal.
Several unrelated languages and language families show the pattern, which suggests the idea arose more than once. Three of the best known are Basque, Georgian and Yoruba, which are not related to one another.
Basque
Basque counts in twenties for its tens above twenty. The word for twenty is hogei, and forty is berrogei, which is generally analysed as meaning two twenties. Sixty is hirurogei, three twenties, and eighty is laurogei, four twenties. Numbers between the twenties are built by addition: thirty is hogeita hamar, which can be glossed as “twenty and ten”.
Basque is a language isolate, with no demonstrated relatives, so its system cannot be explained as inherited from a neighbour. Some neighbouring Romance languages show traces of twenty-counting as well, and how much contact shaped each is debated.
Georgian
Georgian, a Kartvelian language of the Caucasus, is probably the most thoroughly vigesimal of the group. Twenty is ots, forty is ormots (two twenties), sixty is samots (three twenties) and eighty is otkhmots (four twenties). The numbers in between are formed on the same plan: thirty is otsdaati, roughly “twenty and ten”, and fifty is ormotsdaati, “forty and ten”. The higher units, such as one hundred, have their own words.
The pattern is regular, so learners can predict the forms once they have the basic pieces. A speaker does not usually experience this as an exotic way of counting, just as an English speaker does not think about “teen” as meaning ten.
Yoruba
Yoruba, spoken mainly in Nigeria and Benin, also uses twenty as a building block, and adds a second device: subtraction. Many numbers are named by taking a smaller number away from a round one, so fifteen is formed as roughly “five from twenty”. Larger numbers, such as forty, are expressed in multiples of twenty. The result is a system in which a speaker may need to do a little arithmetic just to say a number, which is part of why Yoruba is a regular example in discussions of how number words are put together.
Yoruba shows that a base is not the only feature. How a language handles numbers in between, by addition, multiplication or subtraction, varies as much as the base.
The score in older English
English is a decimal language, yet it kept a word for twenty. A score is twenty, and the word is usually traced to a term meaning a notch or tally mark, which links it to the practice of marking groups of twenty on a stick when counting animals. The King James Bible gives a lifespan as “threescore years and ten”, meaning seventy. President Abraham Lincoln’s Gettysburg Address, in 1863, opens with “four score and seven years ago”, which is eighty-seven.
These phrases are best seen as survivals, not as evidence that English once counted in twenties. They sit alongside the other traditional counting units such as the dozen, and the score has largely faded from everyday speech.
Other vigesimal traces
French is the best-known European example in daily use, where eighty is quatre-vingts, literally four twenties; the details belong with French number names. Belgian and Swiss varieties often use decimal-style words for seventy and ninety instead. Danish is more strongly vigesimal: its word for fifty is usually explained as meaning two and a half twenties, and sixty is three twenties.
Beyond Europe, the Maya built a written system around twenty, as described under Maya numerals, and several other languages of the Americas count in twenties. Some Indo-European numerals have been argued to show twenty-counting traces, but opinions vary.
Why it matters
Vigesimal counting is a reminder that ten is not a law of nature. A base reflects habit, history and the body, and often a mixture of all three. Comparing languages shows how number words can encode different arithmetic, and that any one system can be learned and used with ease by the people who grew up with it.