以ㄧˇyǐ子ㄗˇzǐ之ㄓzhī矛ㄇㄠˊmáo，攻ㄍㄨㄥgōng子ㄗˇzǐ之ㄓzhī盾ㄉㄨㄣˋdùn

比喻以對方的觀點、理論來反駁對方。語本《韓非子·難一》：「楚人有鬻楯與矛者，譽之曰：『吾楯之堅，物莫能陷也。』又譽其矛曰：『吾矛之利，於物無不陷也。』或曰：『以子之矛，陷子之楯何如？其人弗能應也。』」

英lit. use sb's spear to attack his shield (idiom, derived from Han Feizi 韓非子); turning a weapon against its owner, fig. to attack an opponent using his own devices, hoist with his own petard