Belief revision and default reasoning : syntax-based approaches

Belief revision leads to temporal nonmonotonicity, i.e., the set of beliefs does not grow monotonically with time. Default reasoning leads to logical nonmonotonicity, i.e., the set of consequences does not grow monotonically with the set of premises. The connection between these forms of nonmonotonicity will be studied in this paper focusing on syntax-based approaches. It is shown that a general form of syntax-based belief revision corresponds to a special kind of partial meet revision in the sense of variants of logics for default reasoning. Additionally, the computational complexity of the membership problem in revised belief sets and of the equivalent problem of derivability in default logics is analyzed, which turns out to be located at the lower end of the polynomial hierarchy

Group peer disagreement

A popular view in mainstream social epistemology maintains that, in the face of a revealed peer disagreement over p, neither party should remain just as confident vis-a-vis p as she initially was. This ‘conciliatory’ insight has been defended with regard to individual epistemic peers. However, to the extent that (non-summativist) groups are candidates for group knowledge and beliefs, we should expect groups (no less than individuals) to be in the market for disagreements. The aim here will be to carve out and explore an extension of the conciliatory insight from individual peer disagreement to group peer disagreement; in doing so, I’ll raise and address three key problems that face any plausible defence of such a constraint