MENTAL MODEL · M13295

Defeasible Reasoning

TechnicalHigh supportArtificial Intelligence

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Updated 2026-09-10

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INTRODUCTION

English translation pending.

CORE DEFINITION

When an argument is rationally compelling without being deductively valid, it is defeasible: the truth of the premises supports the conclusion, yet a case in which the premises are true and the conclusion false may still arise, so the support relation is provisional. Default inference, autoepistemic reasoning, and much legal reasoning have this character.

SCAFFOLDING EFFECT

psychology

Reduce cognitive load

- Default advancement: when information is incomplete, infer by default rule first, while presupposing the conditions under which it could be rebutted. - Belief revision: when new evidence appears, withdraw old conclusions according to their strength, keeping the belief set revisable.

anchor

Anchor fast decisions

Defeasible reasoning holds because the relation between premises and conclusion is not entailment but a default link of the form that it holds unless there is an exception. Default rules let us infer ahead while information is incomplete, while retaining the possibility of defeat by stronger contrary information, so the belief set can be revised with new evidence.

MINIMUM ACTION

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Practice this model in one real situation:

Determine whether the inference at hand is deductively necessary or a default inference, and make its defeasibility explicit. 2. List the exceptions and counterexamples that could defeat it, and check whether available information already rules them out. 3. When new evidence appears, re-evaluate the conclusion and withdraw it if necessary rather than clinging to it.

Check to track your progress (stored locally)

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Source support: Explicit

link
plato.stanford.eduhttps://plato.stanford.edu/entries/reasoning-defeasible/ZH · Explicit
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