When it comes to counting, eleven and twelve are the odd men (well, numbers) out. In other languages, these numbers have some sort of uniformity with each other and the other numbers between 10 and 20. Take Spanish, where 11 is once, 12 is doce, and 13 is trece. French has a similar pattern (onze, douze, treize) and so does Italian (undici, dodici, tredici). Why are eleven and twelve so different from thirteen, fourteen, and the rest of the teens?
Our linguistic ancestor, Old English, called these numbers “endleofan” and “twelf,” which come from the Proto-Germanic “ainlif-“ and “twa-lif-.” “Lif” is the root of the verb, “leave.” Combined with the numbers “ain” and “twa,” those words literally translate to “one left” and “two left,” which describes how far the numbers are “over ten.” Makes sense, right? (We can also thank Old English for the mysterious “R” in “Mrs.”)
What doesn’t make sense is why the “lif” root didn’t catch on for other numbers, but that’s just the way the English number system evolved. People used 11 and 12 more often in daily life, so those pronunciations slowly became permanent parts of the language. While the other numbers between 10 and 20 eventually got their own form of “lif” (the suffix “-teen” actually comes from “ten”), 11 and 12 stayed pretty much the same.