  The Mohists refer to the objective ethical standard they seek as a fa (model, standard), a concept that plays a central part in their ethics and their views on language, knowledge, and argumentation or reasoning. Fa is among the key notions through which Mohism had an important influence on the late Warring States Confucian thinker Xunzi and his student Han Fei, leading representative of a style of realpolitik thought that later became known as the fa jia (school of fa, often translated as “legalism”). Fa have a dual role, providing both practical guidelines and justificatory criteria for judgment and action. In their action-guiding role, fa serve as guidelines or decision criteria that direct action and practical reasoning. In this respect, they are an important part of the Mohists’ explanation of how we learn language and ethical norms and of the cognitive processes by which we reason, form judgments, and act. In their justificatory role, on the other hand, fa may function as fundamental standards of correctness by which to justify actions and judgments.