Did you know that English is full of little unspoken rules? One of these strange rules happens in ablaut reduplication, which is the repetition of a word with a change in one of its vowels. Terms like criss-cross, Kit-Kat and sing-song are examples of this linguistic phenomenon.
But have you ever noticed that there’s a pattern to these phrases? Try saying them backwards: cross-criss, Kat-Kit, song-sing. It just doesn’t feel right. It turns out that there is a specific order to the vowels we use in these phrases. We always start with the “high” vowels and move progressively towards the “low” vowels. A high vowel, like the iin criss-cross, is formed when your tongue is closer to the roof of your mouth, while a low vowel like the o in sing-song is formed with your tongue in a lower position.
One theory of why we do this is because low vowels are closer to our mouth’s natural resting position, so it’s easier to start in an unnatural position and work our way back to normal. So the order of these phrases will always be I-A-O: sing sang song!
Ohio State University Department of Linguistics,Language Files: Materials for an Introduction to Languages and Linguistics (Ohio State University Press, 2016), 59–60.