First-order conditional logic revisited

Nir Friedman*, Joseph Y. Halpern, Daphne Koller

*Corresponding author for this work

Research output: Contribution to conferencePaperpeer-review

8 Scopus citations


Conditional logics play an important role in recent attempts to investigate default reasoning. This paper investigates first-order conditional logic. We show that, as for first-order probabilistic logic, it is important not to confound statistical conditionals over the domain (such as `most birds fly'), and subjective conditionals over possible worlds (such as `I believe that Tweety is unlikely to fly'). We then address the issue of ascribing semantics to first-order conditional logic. As in the propositional case, there are many possible semantics. To study the problem in a coherent way, we use plausibility structures. These provide us with a general framework in which many of the standard approaches can be embedded. We show that while these standard approaches are all the same at the propositional level, they are significantly different in the context of a first-order language. We show that plausibilities provide the most natural extension of conditional logic to the first-order case: We provide a sound and complete axiomatization that contains only the KLM properties and standard axioms of first-order modal logic. We show that most of the other approaches have additional properties, which result in an inappropriate treatment of an infinitary version of the lottery paradox.

Original languageAmerican English
Number of pages8
StatePublished - 1996
Externally publishedYes
EventProceedings of the 1996 13th National Conference on Artificial Intelligence. Part 2 (of 2) - Portland, OR, USA
Duration: 4 Aug 19968 Aug 1996


ConferenceProceedings of the 1996 13th National Conference on Artificial Intelligence. Part 2 (of 2)
CityPortland, OR, USA


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