The Logic of Trust

This thesis addresses two problems of trust:

1. Knowledge on Trust: If we are provided with information by a variety of individuals, whom we trust to different degrees, what is the best overall theory we can form from the information we are given?

2. Social Trust: If one does not have direct experience of an individual, how can one establish an initial degree of trust through the offices of society?

It addresses the first problem by developing a formal, mathematical and computational, model of Bonjour’s Coherence Theory of Knowledge, and the second by adapting abstract argumentation theory to reason about networks of relationships of trust and distrust between individuals. In developing the latter it develops a notion of generalised argumentation systems, giving their semantics via the Galois Connections induced by binary relations, and provides a general scheme of evaluation of these systems based on propositional model finding.
Throughout, some effort is made to set the work in the context of both theories of trust and of the day-to-day trust situations that one encounters in everyday life.