How does the Celtic system of counting by twenties compare with counting systems in English and French?

The system of counting by twenties, known as a vigesimal system, is an innovation found in Celtic languages that is also present in several other languages, including English, French, Danish, and Basque.12

While modern English and French primarily utilize a decimal number system based on the number 10, both languages retain vestiges of the vigesimal system. In French, this is explicitly evident in the word quatre-vingts, which literally translates to "four twenties" for the number 80. In English, the base-20 influence survives in the term "score," famously used in the Gettysburg Address ("Four score and seven years ago") and historically in phrases like "three score and ten".132

Unlike these languages, where the vigesimal system exists as a remnant or innovation, the system is considered an old feature in Basque. In all these cases, the use of 20 as a base is often attributed to the inclusion of toes alongside fingers in early counting methods.23