Yoshiaki Okubo and Makoto Haraguchi
This paper presents a computational model for attacking legal arguments. Assume that, for a case with which we are concerned, an opponent side has constructed a legal argument based on analogical interpretation of a statute. In our model, the argument is attacked by pointing out the incoherence of the analogical interpretation of the statute. To examine such incoherence, we create a hypothetical case C' that is similar to the case in question, with the help of a Goal-Dependent Abstraction framework. Intuitively speaking, we create C' based on a similarity that is consistent with the similarity based on which the opponent's analogical interpretation has been made. Therefore, we can reasonably consider from the viewpoint of legal stability that the statute should be analogically interpreted to apply it to C' if we accept the opponent's interpretation. The incoherence of the analogical interpretation can be examined by finding a precedent in which the statute has been applied to C' based on complete interpretation. It should be noted that a legal argument based on complete interpretation of the statute has a conclusion that is opposite to that of the argument based on analogical interpretation. Therefore, if we find such a precedent, we attack the opponent's argument by pointing out the incoherence of interpretation of the statute and presenting a counterargument having the opposite conclusion.
Keywords: Legal argumentation, Incoherence of interpretation of statute, Similarity, Goal-Dependent Abstraction