Bench-Capon, Trevor; Atkinson, Katie
Abstract: Horty, Rigoni and Prakken have developed formal characterisations of precedential constraint based on dimensions and factors as developed in HYPO and CATO. We discuss these concepts and the relations between them and describe the current models of precedential constraint based on factors, and some criticisms of them. We argue that problems arise from ignoring the structure of legal cases that is provided by the notion of issues, and that seeing precedential constraint in terms of issues rather than whole cases provides a more effective approach and better reflects legal practice. The advantages of the issue based approach are illustrated with a concrete example. We then discuss how dimensions should be accommodated, suggesting that this is best done by seeing reasoning with legal cases as a two stage process: first factors are ascribed to cases and then factor based reasoning can be used to arrive at a decision. Thus precedential constraint can be described in terms of factors, dimensions being handled at the first stage. Both stages are constrained, in different ways, by precedents: we identify three types of precedent: framework precedents which structure cases into issues, preference precedents which resolve conflicts between opposing sets of factors within these issues, and ascription precedents which constrain the mapping from facts to factors.