Many people have proposed representing facts about what is
``normally'' the case. One problem is that every object is abnormal
in some way, and we want to allow some aspects of the object to be
abnormal and still assume the normality of the rest.
We do this with a predicate ab standing for ``abnormal''. We circumscribe
. The argument of ab will be some aspect of the entities
involved. Some aspects can be abnormal without affecting others. The
aspects themselves are abstract entities, and their unintuitiveness is
somewhat a blemish on the theory.
The idea is illustrated by the examples of the following sections.