One of the reasons numbers are so useful is that they’re predictable. The difference between 100 and 101 is the same as the difference between 101 and 102. The words we use for numbers are usually predictable too – twenty-three comes after twenty-two, and thirteen comes after… twelve? Eleven and twelve stick out like sore thumbs in our number system, but why?
The word eleven comes from the Old English endleofan, which comes from Proto-Germanic *ainalif. This word is a compound of the Proto-Germanic *ainaz meaning ‘one’ and *lif meaning ‘left over’ (i.e., after counting to ten), giving us the meaning 10 + 1. Twelve follows that same pattern, coming from Proto-Germanic *twalif from *twa ‘two’ and *lif, giving us 10 + 2.
Eleven and twelve are derived from these two words in most Germanic languages (like ellefu in Icelandic and twaalf in Dutch), and then switch to a different pattern. Interestingly enough, in Lithuanian (which is not a Germanic language but rather a Baltic language), numbers 11 to 19 are all formed using the ‘left over’ system, with trylika for ‘thirteen’, keturiolika for ‘fourteen’, and so on. This system probably came from Germanic some 1200 years ago, and has stood the test of time.
Confirming that eleven and twelve do mean the numbers after 10 is easy, but the reason the pattern of 1 and 2 left over doesn’t continue for the next seven numbers is still a mystery. A popular hypothesis is that at one point the Germanic spoken number system only went as far as ten, so anything over that was either ‘more’, or counted in a different way. For now, though, we’ll just have to live with the fact that we say ‘eleven’ instead of ‘oneteen’.
(Note: the * in front of Proto-Germanic words indicates that they are reconstructed words. Languages with no recorded history are reconstructed via a process of comparing their descendent languages, finding similarities, and using known facts about language change over time.)
