Non-monotonic reasoning allows conclusions to be retracted when new information is introduced. It is used to model plausible reasoning where defaults may be overridden. For example, it is typically true that birds fly, so we could conclude that Tweety flies since Tweety is a bird. However, if we are later told Tweety is a penguin, we would retract the conclusion that Tweety flies since penguins do not fly despite being birds. Non-monotonic reasoning resolves inconsistencies by removing conclusions derived from default rules when specific countervailing information is received.

1. GANDHINAGAR INSTITUTE OF TECHNOLGY
Department of Information Technology
Logics For Non-monotonic
Reasoning
Student Name(Enroll No): Shaishav Shah(170120116094)
Name of Faculty: Prof. Anirudhdha Nayak
AI(2180703)

2. Non-monotonic Reasoning
• A non-monotonic logic is a formal logic whose
consequence logic is not monotonic.
• Logic is non-monotonic if the truth of a
preposition may change when new information
(axioms) is added.
• Allows statement to be retracted.
• Used to formalize plausible (believable)
reasoning.

3. Example 1
– Birds typically fly. Tweety is a bird.
– Tweety (presumably) flies.
• Conclusion of non-monotonic argument may not
be correct.

4. Example 2
– If Tweety is a penguin, it is incorrect to conclude
that Tweety flies.
(incorrect because, in example 1, default rules when
case-specific information was not available.)
• All monotonic reasoning are concerned with
consistency.
• Inconsistency is resolved, by removing the
relevant conclusion(s) derived by the default rules,
as shown in the next example.

5. Example 3
• The truth value(true or false), of prepositions such
as “Tweety is a bird” accepts default that is
normally true, such as “Birds typically fly”.
– A conclusion is derived was “Tweety flies”.
• When an inconsistency is recognized, only the
truth value of the last type is changed.

6. Thank You