Looking at the dictionary, both 任せる and 任す seem to have the same meaning and they're both transitive verbs, so I wonder if there is any difference between them. Is there any situation where one of them is preferred over the other?

They seem to both have the meaning "to entrust ... to another". There are also some expressions listed for 任せる like 想像に任せる and 成り行きに任せる. Can they also be used with 任す?

And why are there even two variants in the first place? There are many pairs of verbs with the same structure where one of them is equal to the other except for ending with -eru and one of them is transitive and the other intransitive. So why can't one of them be intransitive?

  • Not 100% sure, but theres a common phenomenon, mostly related to the dialectical differences between eastern and western japan, where transitive verbs are conjugated differently in this way. For example, here in Hiroshima we say 見して instead of 見せて. You might hear 食べさす instead of 食べさせる, and so on... I would assume that this words are simply variants in the above way. However, its probably best to leave fixed expressions how they are, 伝わりやすいよね?
    – Lucas
    Commented Jun 22, 2021 at 23:31
  • I looked these two verbs up in two of my dictionaries. In one, for 任せる it referred the reader to the main entry as 任す; in the other, it was the other way around. I just looked in a third dictionary (yes, I have way too many dictionaries), and it also refers the reader to the other entry (任す to 任せる). All three dictionaries are Japanese language dictionaries from different publishers. None give any hint that the two variants are significant in any way. As to why, I don't have a clue.
    – A.Ellett
    Commented Jun 23, 2021 at 0:48

1 Answer 1


They are mostly interchangeable. 想像に任せる and 想像に任す mean the same thing. 任せた and 任した are the same, too. The godan version, 任す, sounds slightly more literary and uncommon to me. In particular, 任す almost never takes the imperative form (任せ!).

There are similar verb pairs, including:

  • 済ませる / 済ます
  • 巡らせる / 巡らす
  • 驚かせる / 驚かす
  • 寝かせる / 寝かす

See also: Could not understand why 命令形 (imperative form) is used in this sentence from 1Q84 book

  • Like short causative forms, 任す is not uncommon in Western dialects. It never occurred to me that it sounds literary but, if it does, it may be because it’s the older form.
    – aguijonazo
    Commented Jun 23, 2021 at 7:29

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