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効果, 有効, 効き目, 効力, 効能, 影響, and 作用 all have meanings than can roughly be
translated to "effect" or some variation of the word.

My understanding is:

  * 影響 and 作用 are the only ones that aren't strictly positive sounding
  * 作用 is typically used for natural/scientific effects, like chemical reactions or graviational laws
  * 効果 and 効能 are more like "effect" while 有効, 効き目, and 効力 are more like "effective"

But beyond this, I have a difficult time understanding when to use them
properly.
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2022-09-29T16:20:46.987
96409
2022-10-01T04:54:22.900
38831
question
word-choice nuances
How to use the various Japanese words involving effect
Your understanding seems fine.

  * **効能** [noun]: Refers to positive/expected effects of a therapy/medicine/onsen/etc.
  * **効き目** [noun]: Almost the same as 効能, but it is a wago (see [wago-and-kango](/questions/tagged/wago-and-kango "show questions tagged 'wago-and-kango'")) and tends to be avoided in academic contexts.
  * **効力** [noun]: Can be used in the same way as 効能 in therapeutic contexts, but mainly used in other contexts in the sense of validness/activeness, as in "the law is in _effect_ ", "the rule took _effect_ ".
  * **効果** [noun]: Almost the same as 効能 in therapeutic contexts. Also used in other contexts in the sense of illusion/tricks/decoration, as in "visual/audio _effect_ ".
  * **作用** [noun, suru-verb]: Tends to refer to direct effects at a more mechanical level (physics, physiology, etc). This is a neutral word that does not assume the effect is desirable. 副作用 ("side effect") is an important derivative word.
  * **影響** [noun, suru-verb]: Closer to "influence" rather than "effect".
  * **有効** [na-adj]: "Effective". The only na-adjective among these.

So "This drug is effective" can be translated as この薬には効能がある, この薬には効き目がある,
この薬には効果がある and この薬は有効だ. この薬には作用がある makes little sense unless this was said as
opposed to placebo.

Related:

  * [Difference between 影響 and 効果](https://japanese.stackexchange.com/q/76815/5010)
CC BY-SA 4.0
2022-10-01T04:54:22.900
96432
2022-10-01T04:54:22.900
5010
96409
answer