Default reasoning in natural language processing

In natural )a~gnage, as in other computational task domains it is impox~ant tc~ operate by default assumptions. First, m~my constraints re(tni~'exl h)r constraint propagation are initially tmspecified, Second, in highly ambiguous tasks such as text analysis, ambiguity can be reduced by considering more plansi-. hie scenarios first. Default reasoning is problematic for firstorder logic when allowing non-monotonic inferences. Whereas in monotonic logic facts can only be asserted, in non-monotonic logk: a system must be maintained consistent even as previously assumed defaults are being retracted.