Deductive coherence and norm adoption

This paper is a contribution to the formalisation of Thagard's coherence theory. The term coherence is defined as the quality or the state of cohering, especially a logical, orderly, and aesthetically consistent relationship of parts. A coherent set is interdependent such that every element in it contributes to the coherence. We take Thagard's proposal of a coherence set as that of maximising satisfaction of constraints between elements and explore its use in normative multiagent systems. In particular, we interpret coherence maximisation as a decision-making criterion for norm adoption. We first provide a general coherence framework with the necessary computing tools. Later we introduce a proof-theoretic characterisation of a particular type of coherence, namely the deductive coherence based on Thagard's principles, and derive a mechanism to compute coherence values between elements in a deductive coherence graph. Our use of graded logic helps us to incorporate reasoning under uncertainty, which is more realistic in the context of multiagent systems. We then conduct a case study where agents deliberate about norm adoption in a multiagent system where there is competition for a common resource. We show how a coherence-maximising agent decides to violate a norm guided by its coherence. © The Author 2009. Published by Oxford University Press. All rights reserved.