Why does ~させる get to be an "official" auxiliary verb/conjugation form but ‘~入れる‘ doesn't?

Is there even such a thing as an “official” list actually? Or even an “auxilliary verb” in the first place, or is it just verbs that are commonly used as suffixes are classified post-facto as auxilliary after they reach a certain level of popularity?


This is more my impression than an authoritative answer, but I think an auxiliary verb should:

  • work with pretty much every verb to make a change in meaning that you can understand just from knowing meanings of the base verb and the auxiliary verb
  • be doing a basically grammatical job, like negation or indicating tense or making something passive or showing that an action is being done for somebody else

If you do a search for “Japanese auxiliary verbs” (or 助動詞 if you want Japanese resources) you will find plenty of resources discussing the topic, ranging from academic articles to lessons to discussions.

Tofugu has an article here: Kobun (Classical Japanese) and How To Use Helper Verbs

There is a list here: Appendix:Japanese auxiliary verbs - Wiktionary, the free dictionary and here: List: auxiliary verb - JapanDict: Japanese Dictionary