https://en.wikipedia.org/wiki/Grammaticalization
Examples of full grammaticalization フランス語の未来形
An illustrative example of this cline is in the orthography of Japanese compound verbs.
Many Japanese words are formed by connecting two verbs, as in "go and ask" (行って聞く ittekiku?), and in Japanese orthography lexical items are generally written with kanji (here 行く and 聞く), while grammatical items are written with hiragana (as in the connecting て).
↑ 変 ？
Compound verbs are thus generally written with a kanji for each constituent verb, but some suffixes have become grammaticalized, and are written in hiragana, such as "try out, see" (〜みる -miru?), from "see" (見る miru?), as in "try eating (it) and see" (食べてみる tabetemiru?).