##  [Belief Revision](/belief-revision-0) 

 Definition

The methodological process of incorporating new information into a belief set while maintaining consistency and minimizing unnecessary change; concerned with how to add, remove, or change beliefs coherently.

 

 

 

 

 

 





## Principle

Principle

Operations partition into expansion (add without checking consistency), contraction (remove a belief while losing as little else as possible), and revision (incorporate a new belief consistently by appropriate contraction); minimal change and epistemic entrenchment guide choices.

 

 

 

 

 





## Demonstration

Demonstration

An agent believes both p and q; upon receiving evidence ¬p, the agent must revise its belief set—either by retracting p and dependent beliefs or by modifying related assumptions—to restore consistency while preserving maximal remaining beliefs.

 

 

 

 

## Misapplication

Misapplication

Blindly accepting the most recent input or repeatedly oscillating between contradictory states without accounting for evidence strength or entrenchment, leading to unstable knowledge bases.

 

 

 

 

 





## Consequence

Consequence

Produces a coherent, updated belief set that reconciles new information with prior commitments while preserving as much prior information as possible, enabling rational adaptive behavior in changing environments.

 

 

 

 

## Reversal

Reversal

Radical replacement: discard all prior beliefs when new information arrives regardless of compatibility or evidential weight, sacrificing continuity for immediacy.

 

 

 

 

 





## Boundary

Boundary

Applies to belief sets formalized as logically closed sets of sentences or to structured epistemic states with ordering of beliefs; does not directly cover probabilistic updating procedures (though formal links exist) and excludes non-logical cultural or social belief change models.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Tension with simple nonmonotonic inference: both allow retraction of conclusions, but belief revision focuses on global coherence of belief sets under explicit change operations while nonmonotonic systems focus on local defeasible inference; also tension with Bayesian conditionalization over numeric credences.

 

 

 

 

 





## Synthesis

Synthesis

Belief revision is the principled set of operations—expansion, contraction, revision—applied to an agent's belief state to incorporate new information while preserving consistency and minimizing loss, governed by minimal-change criteria and belief ordering.