Coherence-based reasoning in Australian contract law adjudication with broad principles and detailed rules

Simon (1998; 2004) presented a psychological model of legal adjudication known as coherence-based reasoning. Coherence-based reasoning extends from a constraint satisfaction understanding of reasoning, and is typified by the presence of a coherence shift. The model has been successfully measured empirically using legal decision tasks (Holyoak & Simon, 1999). The current thesis explores coherence-based reasoning as an explanatory model within the context of complex contract law adjudication. The ecological validity of the model was examined in relation to multiple legal factors including legal expertise, dispute difficulty, decision confidence and legal utility. Coherence-based reasoning was demonstrated to be a suitable explanatory model for the reasoning process of judging real Australian contract law disputes. Particular interest was directed toward measuring the coherence shift, legal consensus and utility of deciding contract law disputes with systems of legal rules that differ on their level of specificity. Broad principles were compared to detailed rule law models in order to contribute empirical evidence to the ongoing jurisprudential debate regarding the optimal expression of contract laws in Australia. The results indicated that using broad principles to guide decision making produces greater decision consensus than using detailed rules, but only for disputes that are easier to decide. For harder disputes, the use of broad principles produced lower decision consensus than the use of detailed rules. Decision consensus among participants who used detailed rules to guide their decision making was moderate, and there was no difference in consensus between easier and harder disputes. For all levels of dispute difficulty and for all law models, a coherence shift was demonstrated and participants reported moderate to high levels of decision confidence.