, Volume 18, Issue 2, pp 93–96 | Cite as

Conditionalization, A New Argument For

  • Bas C. van Fraassen


Probabilism in epistemology does not have to be of the Bayesian variety. The probabilist represents a person's opinion as a probability function; the Bayesian adds that rational change of opinion must take the form of conditionalizing on new evidence. I will argue that this is the correct procedure under certain special conditions. Those special conditions are important, and instantiated for example in scientific experimentation, but hardly universal. My argument will be related to the much maligned Reflection Principle (van Fraassen, 1984, 1995), and partly inspired by the work of Brian Skyrms (1987).


Convex Combination Prior Opinion Epistemic Situation Reflection Principle Orthogonal Family 
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  1. Skyrms, B.: 1987, 'Dynamic Coherence and Probability Kinematics', Philosophy of Science 54, 1–20.CrossRefGoogle Scholar
  2. van Fraassen, B.: 1984, 'Belief and the Will', Journal of Philosophy 81, 235–256.CrossRefGoogle Scholar
  3. van Fraassen, B.: 1989, Laws and Symmetry, Oxford: Oxford University Press.CrossRefGoogle Scholar
  4. van Fraassen, B.: 1995, 'Belief and the Problem of Ulysses and the Sirens', Philosophical Studies 77, 7–37.CrossRefGoogle Scholar

Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • Bas C. van Fraassen
    • 1
  1. 1.Princeton UniversityUSA

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