Ablaut Reduplication is a linguistic phenomenon where native English speakers unconsciously follow a grammar rule when using reduplicated words such as tick-tock and King-Kong. This rule, first spotted by Mark Forsyth, states that if there are three words, the order must be I, A, O. If there are two words, the first is I and the second is either A or O. This pattern is followed in every example of the English language.
The reason for this rule is based on the high vs. low vowel distinction, where the first vowel is always high, and the second is low. The difference between high and low vowels is based on the height of the tongue within the mouth when producing the sound.
High vowels are produced with the tongue positioned close to the roof of the mouth, while low vowels are produced with the tongue positioned further down towards the bottom of the mouth. Some examples of high vowels are the sounds in "bit", "beat", and "bat", while some examples of low vowels are the sounds in "bot", "boat", and "bought".
Furthermore, linguist Steven Pinker explains that “words that connote me-here-now tend to come before words that connote literal or metaphorical distance from “me” (or a generic speaker): here and there (not there and here), this and that, now and then, father and son, man and machine, friend or foe, Serbo-Croatian (among Serbs), Croat-Serbian (among Croats). The syllogism seems to be: “me” = high front vowel; me first; therefore, high front vowel first.