Soixante-dix, quatre-vingts, quatre-vingt-dix? Why All the Trouble? We know in French, 70 is soixante-dix, 80 is quatre-vingts and 90 is quatre-vingt-dix, while in some other regions, people say septante(70), octante(80), huitante(80) and nonante(90). So why all the trouble? Let's have a look at the regions where septante(70), octante(80), huitante(80) and nonante(90) are in current use: Septante and nonante are commonly used in Belgium and Switzerland. The French speakers in Luxembourg use nonante, but no septante. People in Quebec use soixante-dix(60+10) much more than septante(70). I also heard that soixante-dix(60+10) was written in the French textbooks used in German district of Switzerland. Besides, in some areas of France and Italy, and also in some African countries invaded by Belgium in the history, people use septante(70) and nonante(90). That's probably how it is. I believe that the normal 70, 80 and 90 appeared in the languages before the complicated version did. So I've been curious where the trouble for us language learners was from? A book on French linguistics Q&R part explains the origin of soixante-dix(60+10) this way: How do children count? They count one by one, "One, two, three, four..." So when they got soixante-neuf(69), what's next? Soixante-dix(60+10) of course! Children may probably go on like this, "Soixante-dix(60+10)、soixante et onze（60+11）、soixante-douze(60+12)", and parents thus try to straighten them, but in vain. So they surrendered and gave up septante(70). Really? Are you kidding me?! So how do you expect me to understand this? French parents are the best ever?! Let's go on... So how about 80? Well, our ancestors used to do counting by carving gaps on a stick. One gap was counted as 20, so four gaps were 80. The "four gaps" was so popular that it survived. It has completely replaced traditional octante(80), huitante(80) here and driven them out to Switzerland. As for quatre-vingt-dix(90), it probably has the similar origin of Soixante-dix(60+10). So I threw away the crap. Here comes the official answer: In Middle Age, French were inclined to count twenty by twenty. Therefore, vint et dis(20+10), deux vins(2×20), and trois vins(3×20) exist in classic French. Later, trente(30), quarante(40), cinquante(50), soixante(60) came into being and started to compete with them, and won. But why they kept complicated 70, 80 and 90? Nobody knows. They were eventually preserved by L’Institut de France. So, nobody knows. The only explanation can be: Juste pour nous compliquer la vie!