There is a nonmonotonic logic which: (i) is suitable for default
reasoning; (ii) came right from the beginning with an implementation; and
(iii) is more general than  other  approaches which have been
proposed recently. In fact this logic has been known for over 10 years now: 
it is Nute's defeasible logic. Despite these obvious advantages the logic is 
not in the mainstream of nonmonotonic reasoning, mainly because it has not 
been studied sufficiently as a formal system, and because its relationship
to other formalisms has not been studied up to now.</P>

<P>This paper seeks to change the perception of defeasible logic. In
particular, it presents the logic in a formal setting, derives several
properties, including representational results, and gives an
operational semantics. Finally the paper discusses some relationships
of defeasible logic to other default reasoning approaches.