三論宗之語。於者所依之義。佛之說法為教諦，所依之二諦為於諦。是依中論諸佛依此二諦說法之文而立。二諦義上曰：「論云：諸法性空，世間顛倒，思有為世諦。諸賢聖真知顛倒性空，為第一義諦。諸佛依此二諦說法，（中略）今正此一句，明依二諦說法，所依是於諦，說法是教諦也。」
All Buddha's teaching is 'based upon the dogmas' that all things are unreal, and that the world is illusion; a 三論 phrase.