Statutor names an evolving Prolog program which is being developed as a knowledge-based tutoring system in the legal domain. The system utilises direct manipulation of graphical objects as a means of eliciting complex responses from the user and for providing graphical representations of complex answers to the user. It is a marriage of good interface practice and knowledge-based programming techniques which has presented a number of interesting prospects for tutoring. Perhaps the most interesting of these is the possibility of a dialog in which the student is asked to construct an argument in order to establish the truth of a particular proposition, the system then doing the same, and feedback and student modelling information being derived from a comparison of the two argument structures. This technique is not restricted in its significance to the legal domain but is applicable wherever knowledge of a subject matter can be expressed or tested by the construction of an argument. Finally, the system demonstrates the reusability of declarative knowledge by including additional modules (an expert system shall and an authoring system) with utilise the same knowledge bases as the main Statutor program itself.