AGM Postulates
Where K is a belief state, K*A represents the set of
beliefs resulting from revising K with new belief
A.
- (K*1) K*A is closed under logical
consequence.
- (K*2) A belongs to K*A.
- (K*3) K*A is a subset of the logical
closure of K ∪ {A}.
- (K*4) If ¬A does not belong to K,
then the closure of K ∪ {A} is a subset of
K*A.
- (K*5) If K*A is logically inconsistent,
then either K is inconsistent, or A is.
- (K*6) If A and B are logically
equivalent, then K*A = K*B.
- (K*7) K*(A & B) is a
subset of the logical closure of K*A ∪
{B}.
- (K*8) If ¬B does not belong to
K*A, then the logical closure of
K*A ∪ B is a subset of
K*(A & B).
Supplement to Defeasible Reasoning
Stanford Encyclopedia of Philosophy