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Line 1: {{multiple issues\|{{~~Refimprove~~More citations needed\|date=October 2007}} {{Expert ~~subject~~needed\|Philosophy/Epistemology\|date=February 2009}}}} The '''propensity theory of probability''' is [[Probability interpretations\|one interpretation]] of the concept of [[probability]]. Theorists who adopt this interpretation think of [[probability]] as a physical propensity, or disposition, or tendency of a given type of physical situation to yield an outcome of a certain kind, or to yield a long run relative frequency of such an outcome.<ref name="Stanford">'Interpretations of Probability', [[Stanford Encyclopedia of Philosophy]] [http://plato.stanford.edu/entries/probability-interpret/]. Retrieved 23 December 2006.</ref> Line 22: A number of other philosophers, including [[David Miller (philosopher)\|David Miller]] and [[Donald A. Gillies]], have proposed propensity theories somewhat similar to Popper's, in that propensities are defined in terms of either long-run or infinitely long-run relative frequencies. Other propensity theorists (''e.g.'' [[Ronald Giere]] <ref>{{cite book \|author=Ronald N. Giere \|title=Studies in Logic and the Foundations of Mathematics \|chapter=Objective Single Case Probabilities and the Foundations of Statistics \|doi=10.1016/S0049-237X(09)70380-5 \|volume=73\|year=1973 \|pages=467–483 \|isbn=978-0-444-10491-5\|author-link=Ronald N. Giere }}</ref>) do not explicitly define propensities at all, but rather see propensity as defined by the theoretical role it plays in science. They argue, for example, that physical magnitudes such as [[electrical charge]] cannot be explicitly defined either, in terms of more basic things, but only in terms of what they do (such as attracting and repelling other electrical charges). In a similar way, propensity is whatever fills the various roles that physical probability plays in science. Other theories have been offered by [[D. H. Mellor]],<ref>{{cite book \|author=D. H. Mellor \|title=The Matter of Chance \|url=http://www.dspace.cam.ac.uk/handle/1810/183661 \|publisher=Cambridge University Press \|year=1971 \|isbn=978-0521615983}}</ref> and [[Ian Hacking]]<ref>{{cite book \|author=Ian Hacking \|title=Logic of Statistical Inference \|url=http://www.cambridge.org/catalogue/catalogue.asp?isbn=9781316508145\|publisher=Cambridge University Press \|year=1965 \|isbn=9781316508145}}</ref> Line 31: * The Principal Principle. Let C be any reasonable initial credence function. Let t be any time. Let x be any real number in the unit interval. Let X be the proposition that the chance, at time t, of A's holding equals x. Let E be any proposition compatible with X that is admissible at time t. Then C(AIXE) = x. Thus, for example, suppose you are certain that a particular biased coin has propensity 0.32 to land heads every time it is tossed. What is then the correct credence? According to the Principal Principle, the correct credence is .32. ==See also==

Propensity probability: Difference between revisions