Defeasibility in Research on AI & Law

In AI & law, defeasible reasoning has been the subject of much research starting from the end of the 1980s. Much of this work focuses on defeasible argumentation (for a survey, see Prakken and Sartor 2015). The possibility of using negation by failure to model defeasible reasoning and burdens of proof in the law was suggested by Sergot et al. (1986). The issue of defeasibility in legal reasoning was first identified by Thomas Gordon (1988, 1995), who later developed the Carneades system into a computable framework for defeasible reasoning (Gordon, Prakken, and Walton 2007).
Hage (1997) proposed the idea of rule application as a general pattern for defeasible reason, where rules deliver their consequences only when they are shown to be both valid and applicable (applicability meaning, in Hage’s terminology, the rule’s antecedent conditions are satisfied). In his framework, a legal rule works as an exclusionary reason, such that arguments applying the rule defeat arguments based on excluded reasons (but they may be defeated by arguments based on other reasons).
Prakken and Sartor developed the first model of defeasible reasoning in law which includes reasoning with (defeasible) rules and with priorities among such rules (Prakken and Sartor 1996). The model has been extended to cover the burden of proof (2009), and has been applied to various aspects of legal reasoning, such as reasoning with precedents (Prakken and Sartor 2008). Prakken has developed the idea of prioritised argumentation in several technical contributions (Prakken 2010, Prakken and Modgil 2011).
The idea of legal reasoning as defeasible argumentation has also been developed by Loui and Norman (2005), who have analysed the way a single defeasible legal inference may result from the compression of various inference steps, and may be attacked by unpacking it and addressing these steps.
Bench Capon (2003) has developed the idea of value-based argumentation, namely, the idea that preferences between arguments are determined by the values endorsed by the audience to which the arguments are directed. Bench-Capon and Sartor (2003) have studied how alternative defeasible theories (sets of premises) can be constructed to explain cases, and how they may be prioritised.
Governatori et al. (2004) have shown how defeasible argumentation can be captured by using defeasible logic, in the manner originally proposed by Nute (1994). Extensions of defeasible logic have been used to capture different aspects of legal reasoning, such as the timing of legal effects (2005) and changes in the law (Governatori and Rotolo 2010).
Finally, I should mention the rich research line on the use of defeasible legal argumentation in the evidence domain and its connections with other approaches to evidence (see Verheij et al. 2016).