Predicate logic and the inferences we perform on it is an example of monotonic reasoning.
In monotonic reasoning if we enlarge at set of axioms we cannot retract any existing assertions or axioms.
Humans do not adhere to this monotonic structure when reasoning:
• we need to jump to conclusions in order to plan and, more basically, survive.
o we cannot anticipate all possible outcomes of our plan.
o we must make assumptions about things we do not specifically know about.

• Default reasoning
• Circumscription
• Implementations: Truth Maintenance Systems