i might have just discovered something?
superficial research is not showing me that anyone else has noticed this, so i just want to note this down
there are a whole bunch of indo-european languages which use 20 as a counting base for larger numbers, like quatre-vingts "four twenties" meaning 80 in French and trì fichead cat 's a seachd deug "three twenty and seventeen" meaning 77 in Scottish Gaelic
this phenomenon is simply not part of proto-indo-european and it does not appear in, for example, Hindi, which implies that it was a uniquely european-region innovation
check this out though, if you look at the extent of the Basque language (Euskara) in history, the only Paleo-European language group that still persists to this day, you will notice a pattern: all the IE languages which use 20 as a counting base all border Paleo-Basque territory
map description basically there's a halo that extends all the way from nearly Santander (Spain) on the west to beyond Andorra to the east, and from nearly Zaragoza (Spain) in the south all the way up to damn near Bordeaux (France) in the north, which means the Paleo-Basque ranged over that whole "elbow" area that pretty much which connects the Iberian peninsula to the rest of Europe - and probably beyond - this is a region around 400km by 600km
and as it turns out, the Basque (Euskaldunak) have had a vigesimal counting system all this time!
it seems reasonable to me that the paleo-Basque people - who long had their own well ingrained counting system and unique written numerals since antiquity - would be the ones that would impress upon the immigrants into Europe the use and practice of larger numbers and this filtered down into the subsequent languages until these other newly-minted European immigrants displaced the Paleo-Basque and other Paleo-European peoples
now you might be wondering about Danish, and we can see that no other Old Norse daughter tongues use this system - so it seems to me like they picked it up from their dealings with the Celtic people from the Gaelic to the Bretons, all of whom the Danes mixed with heavily while other Old Norse groups just did not - after all that is how we ended up with the Danelaw
if you are wondering why it affected French but not Spanish, it is almost certainly because French carries a strong substrate of Frankish - a language which existed in that region long before Latin did; while Spanish is mostly Latin and Arabic - both of which are newer to the area and thus did not pick it up those language features!
actually wait! i just found the tiniest mention of this theory on a Basque language learning site:
Basques have our own vigesimal numbering system. It is also used in other Celtic languages, perhaps as a remnant of a proto-Basque language that was widespread though large areas of Europe.
- Labayru
i bet the only research being done on this is by the Basques themselves, so, hopefully i will run across some Basque linguists who can fill me in on the details
related
this article is just shows that the Basque people of the BCE were literate and amazing artisans, and i found it while looking for evidence of the oldest attested example of the Basque miller numeral system, if you can find any info on its origins i would love to know!
and yes i am going to pretend that Resian does not exist because there just is not enough information available to me on it at this time to determine when or how it got there or if it is even from the same source
