反调（英语: polemic），又称 论战，是一个具争议性的逻辑论证，其意图是创建一个具体了解的真理，及指出相反立场的谬误。论战大多见于很有争议性的话题，该论证的方法或实践称为反调。一个经常写作反调文章，或者说话唱反调的人，是一个辩论者或争论者。原来的英语词是从希腊语: πολεμικός（英语拼音: polemikos）衍生出来的，意思是「好战的，敌对的」，而这个词又来自希腊语: πόλεμος（英语拼音: polemos），即「战争」。

A polemic /pəˈlɛmɪk/ is a contentious argument that is intended to support a specific position via attacks on a contrary position. Polemics are mostly seen in arguments about controversial topics. The practice of such argumentation is called polemics. A person who often writes polemics, or who speaks polemically, is called a polemicist or a polemic. The word is derived fromGreekπολεμικός (polemikos), meaning "warlike, hostile", fromπόλεμος (polemos), meaning "war".