E.g., KB(bird) = bird(Tweety) ? ?x. (ostrich(x) ? bird(x)) ? ? ostrich(Sam) Task: Compute CIRC(KB; bird) Circumscription Axiom: ?bird*. ( KB(bird*) ? (?x.bird*(x) ? bird(x)) ) ? (?x.bird(x) ? bird*(x)) ) Magically choose bird*= x=Tweety ? ostrich(x) This is a formula that satisfies the constraints of the predicate bird in KB and whose extent is not smaller that the extent of bird. …. “Magic” is not a reasonable way to compute circumscription. For certain syntactically restricted KBs, there are systematic methods for computing circumscription.