法律推理领域中的形式逻辑及其不可取代性

The Role,Limits and Irreplaceability of Formal Logic in Legal Reasoning

在法律推理领域,形式逻辑能够阐明、评估法律推理的有效性,增进人们对法律推理的性质与结构的理解,指导法律推理活动。形式逻辑的限度主要表现在:在人们做出法律推理的过程中,它只能提供推论规则,不能提供推理的前提;在人们评估法律论证的过程中,它只能用来评估论证的形式,而不能用来评估论证的内容。形式逻辑不能完成的这两个任务分别由法律方法论与非形式逻辑来承担。但是,不论是法律方法论,还是非形式逻辑,都不能像一些学者设想的那样取代形式逻辑。这在根本上是因为:对于法律推理来说至关重要的推论规则只有在区分推理的形式与内容的前提下才能构造出来,并且只有在一个形式逻辑系统内才能得到检验。只有充分意识到形式逻辑的不可取代性,才能更好地促进它与相关学科在法律推理领域中的协作,从而有效地推动法律推理的理论创新与实践进步。

The role of formal logic in the field of legal reasoning has been questioned ever since Justice Holmes famously declared that“the life of law is not logic but experience”.In recent years,researchers of legal methodology represented by Karl Engisch and Chaim Perelman have tried to embed logic into the study of methodology,believing that logic is an integral part of legal methodology or legal argumentation theory,and calling it“substantive logic”or“legal logic”.The non-formal logic represented by Stephen Toulmin’s argumentation theory even tries to replace formal logic with the so-called“jurisprudence logic”.These claims come from the lack of a clear and systematic understanding of the role and importance of formal logic in legal reasoning.In the field of legal reasoning,formal logic plays an important role in clarifying and evaluating the validity of legal reasoning,deepening the understanding of legal reasoning and guiding legal reasoning activities.Formal logic,of course,is not a panacea;it can neither provide the premises of legal reasoning nor assess the content of legal arguments.But on the one hand,formal logic should not be criticized for not being able to do these things because these tasks should not be undertaken by formal logic,but by legal methodology and informal logic.On the other hand,legal methodology and informal logic cannot replace formal logic.The fundamental reason why legal methodology cannot replace formal logic is that the methodological rules provided by the former and the inferential rules provided by the latter are two distinctive kinds of rules of different natures,and they play different roles in the process of legal reasoning.Through the analysis of the structures,types and schemes of legal argument,informal logic can reveal what issues may be closely related to the argument evaluation,thereby helping us to find the corresponding domain knowledge to assess its content.The systematic understanding of common types of argumentation and their structures will also help us to carry out legal reasoning by constructing and evaluating pro-arguments and con-arguments.However,since it can be used neither to judge whether the premises are true or not nor to judge whether the premises necessarily lead to a conclusion,it cannot replace formal logic either.Since the inferential rules,which are essential to legal reasoning,can be constructed only on the precondition of distinguishing between the form and content of reasoning and can be tested only in a system of formal logic,formal logic plays an irreplaceable role in the field of legal reasoning.Only by fully realizing the functions and limits of formal logic,especially the irreplaceable nature of formal logic,can we better promote the cooperation between formal logic and related disciplines in the field of legal reasoning and thereby effectively promote the theoretical innovation and practical progress of legal reasoning.