Controlled Natural Language in a Game for Legal Assistance

This paper addresses the design of an automated legal assistant capable of performing a logical analysis of legal documents and using natural language as a medium of communication with a human client. We focus on the interplay between natural language in which the legal document is expressed and the formal logic used for reasoning about it — ideally approached using a controlled natural language (CNL) together with an appropriately chosen logic for analysis and reasoning. In translating from CNL to logic, information about the CNL structure is lost. For example, the CNL might contain legal clause numbers, whilst the logic might not. This can lead to problems when for example the reasoning system discovers an inconsistency in the contract and needs to explain its whereabouts to the client. Below we discuss the issues affecting the choice of logic, arguing in favour of keeping certain structural information during formal analysis of legal documents to be able to refer to that structure when interacting with the user. We present a framework in which to experiment and seek solutions to these issues. Having identified a sufficiently restricted domain of application we also report on the development of a CNL to interact with a variant of the game Nomic — a game based on the notion of contract specification and amendment — and argue how this game provides an ideal platform to explore the use of structure information in the domain of legal analysis.