Difference between 任せる and 任す?


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?




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](https://japanese.stackexchange.com/q/86612/5010)




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](https://japanese.stackexchange.com/q/86612/5010)

