Defeasible Reasoning

A Defeasible Reasoning is a Reasoning Argument that is rationally compelling but not deductivelly valid.

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• Example(s):
  • An reasoning argument in which the premises are true but the conclusion is false.
  • Autoepistemic Reasoning.
  • …
• Counter(s):
  • Analogical Reasoning,
  • Logical Reasoning.
• See: Automated Reasoning, Scientist, Premise, Logical Consequence, Material Conditional, Deductive Reasoning, Mathematical Logic, Philosophical Logic, Inductive Reasoning, Problem of Induction, Science, Abductive Reasoning, Wikt:Cogent.

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References

2018

• (Wikipedia, 2018) ⇒ https://en.wikipedia.org/wiki/Defeasible_reasoning#Overview Retrieved:2018-11-3.
  • In logic, defeasible reasoning is a kind of reasoning that is rationally compelling, though not deductively valid.
  • Defeasible reasoning is a particular kind of non-demonstrative reasoning, where the reasoning does not produce a full, complete, or final demonstration of a claim, i.e., where fallibility and corrigibility of a conclusion are acknowledged. In other words, defeasible reasoning produces a contingent statement or claim. Other kinds of non-demonstrative reasoning are probabilistic reasoning, inductive reasoning, statistical reasoning, abductive reasoning, and paraconsistent reasoning. Defeasible reasoning is also a kind of ampliative reasoning because its conclusions reach beyond the pure meanings of the premises.

    The differences between these kinds of reasoning correspond to differences about the conditional that each kind of reasoning uses, and on what premise (or on what authority) the conditional is adopted:

    • Deductive (from meaning postulate, axiom, or contingent assertion): if p then q (i.e., q or not-p)
    • Defeasible (from authority): if p then (defeasibly) q
    • Probabilistic (from combinatorics and indifference): if p then (probably) q
    • Statistical (from data and presumption): the frequency of qs among ps is high (or inference from a model fit to data); hence, (in the right context) if p then (probably) q
    • Inductive (theory formation; from data, coherence, simplicity, and confirmation): (inducibly) "if p then q"; hence, if p then (deducibly-but-revisably) q
    • Abductive (from data and theory): p and q are correlated, and q is sufficient for p; hence, if p then (abducibly) q as cause
  • Defeasible reasoning finds its fullest expression in jurisprudence, ethics and moral philosophy, epistemology, pragmatics and conversational conventions in linguistics, constructivist decision theories, and in knowledge representation and planning in artificial intelligence. It is also closely identified with prima facie (presumptive) reasoning (i.e., reasoning on the "face" of evidence), and ceteris paribus (default) reasoning (i.e., reasoning, all things "being equal").

2017

• (Koons, 2017) ⇒ Robert Koons (2017). "Defeasible Reasoning". In: The Stanford Encyclopedia of Philosophy (Winter 2017 Edition), Edward N. Zalta (ed.).
  • QUOTE: Reasoning is defeasible when the corresponding argument is rationally compelling but not deductively valid. The truth of the premises of a good defeasible argument provide support for the conclusion, even though it is possible for the premises to be true and the conclusion false. In other words, the relationship of support between premises and conclusion is a tentative one, potentially defeated by additional information. Philosophers have studied the nature of defeasible reasoning since Aristotle’s analysis of dialectical reasoning in the Topics and the Posterior Analytics, but the subject has been studied with unique intensity over the last forty years, largely due to the interest it attracted from the artificial intelligence movement in computer science. There have been two approaches to the study of reasoning: treating it either as a branch of epistemology (the study of knowledge) or as a branch of logic. In recent work, the term defeasible reasoning has typically been limited to inferences involving rough-and-ready, exception-permitting generalizations, that is, inferring what has or will happen on the basis of what normally happens. This narrower sense of defeasible reasoning, which will be the subject of this article, excludes from the topic the study of other forms of non-deductive reasoning, including inference to the best explanation, abduction, analogical reasoning, and scientific induction. This exclusion is to some extent artificial, but it reflects the fact that the formal study of these other forms of non-deductive reasoning remains quite rudimentary.

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