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.