Since the first time I saw this occurrence I've been wondering how Japanese people conjugate the "ru" into a n" (ex: 邪魔すんな or なにしてんの?)

1 Answer 1


This is not a conjugation: this is an abbreviation or contraction that happens due to the sounds involved and the biomechanics of the shape of the mouth when articulating these sounds.

This is similar to the process by which English "do not you...?" becomes "doncha...?", or "did you eat yet?" becomes "jeechet?", or "I am going to..." becomes "I'm'a ...".

Note that, in Japanese, the ~る ending only collapses to ~ん when the conditions below are met:

  • the following sound starts with an //n//, such as な or の
    • For instance, you won't see すんひと as a contraction for するひと. The phonology is wrong, since ひと doesn't start with //n//.
  • the context is informal speech
    • For instance, you won't see すんの as a contraction for するの in formal writing, and you won't hear it in formal speech.
  • 1
    I might add one more condition. る tends to be collapsed to ん when the word that starts with /n/ is a particle such as those you listed, but not when it’s a normal noun. For example, テニスをする仲間 usually doesn’t become テニスをすん仲間.
    – aguijonazo
    May 17 at 0:33
  • @aguijonazo, interesting point, yes, it seems that way. Is this something we can say with certainty? May 17 at 0:38
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    It’s hard to draw the line. 中 seems to be a borderline case. すん中で certainly doesn’t sound so natural as すんな or すんの but doesn’t sound so corrupt as すん仲間, either.
    – aguijonazo
    May 17 at 2:17
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    Try saying 思ってるの? fast, and you'll realize it turns into 思ってんの very naturally. Kinda like how "I wanna" developed from "I want to." Say it fast, and it changes naturally.
    – dvx2718
    May 18 at 1:06

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