Modelling rhetorical legal "logic" - a double syllogism

This paper looks at legal reasoning from the point of view of the work of t he lawyer, rather than the law itself. In the case of Common Law systems, t his means a more flexible view of how tasks are divided between the humans and the computer system, with an emphasis on decision support rather than c omplete automation. A process-based model of the lawyer's work is proposed in the form of a double syllogism, which displays an aesthetically pleasing symmetry, but also a significant asymmetry in the role played by perceived precedents. This arises from the use of inductive, rather than deductive, reasoning. The potential complications arising from the issue of the percep tion of precedents are discussed in depth. The double-syllogism model is then considered in the light of CommonKADS te rminology and models. It is suggested that decision support systems using k nowledge-based techniques, as required to support lawyers working under Com mon Law jurisdiction, raise a stronger form of the interaction problem that is well known in knowledge-based systems. This means that such systems are not well catered for in the existing CommonKADS Organisational, Agent, Tas k and Communication Models. The double-syllogism model is suggested as a su pplement to CommonKADS in the development of such systems, at least until a more generic addition is available. (C) 1999 Academic Press.