Polemic memorials (boyi 駁議) were a special type of memorial in which the submitter expressed critical views towards suggestions of others or decisions by the government. The original decision was "refuted and corrected" (bozheng 駁正). The word bo 駁 "impure colour (of a horse)" referred to the heterogeneous composition of such documents. Boyi-style critique was introduced by the Han dynasty 漢 (206 BCE-220 CE). In his book Duduan 獨斷, Cai Yong 蔡邕 (132-192) listed them as one type of memorials to the throne, the others being zhang 章, zou 奏, and biao 表. The submission of boyi critique was usually followed by a discussion between the highest court members.
One of the most famous documents of this type is Liu Zongyi's 柳宗元 (773-819) Bo fuchou yi 駁復仇議 from the Tang period in which he argues against Chen Zi’ang's 陳子昂 (661-702) memorial Fuchou yizhuang 復仇議狀. Of more recent date is Yan Fu's 嚴復 (1854-1921) text Bi Han 辟韓. There is, however, a whole collection of discussions on the state monopolies and related policies of the Han period, namely Huan Kuan's 桓寬 (early 1st cent. BCE) Yantielun 鹽鐵論.