さよういん 作用因 LinksSentence search for 作用因Sentence search for さよういんKanji details for 作, 用 and 因Edit in JMdict Noun1. efficient cause (one of Aristotle's four fundamental types of answer to the question "why?")Philosophy, See also 質料因, See also 形相因, See also 目的因 Discussions Log in to talk about this word.