The Department of Logic & Philosophy of Science Colloquium Series presents

"Explanation, Swamping, and the Principal Principle"
with Katie Elliott, Department of Philosophy, UCLA

January 24, 2014
Social Science Tower, Room 777
3:00-5:00 p.m.

There is no particular opinion about whether or not it will rain that we are rationally obliged to have if we are confident that there has been a change in atmospheric pressure, that there are heavy storm clouds, or even that we see rain approaching. But opinions about the /chance/ of rain (if we have any such opinions) rationally compel us to have a very particular credence that it rains (at least in ordinary cases). Elliott calls this aspect of the relationship between beliefs about objective chances and rational credences “swamping”: a rational agent’s credences in the chance of an outcome determine her credence in that outcome (so long as she only has admissible information). Swamping is a consequence of David Lewis’s “Principal Principle”. Roughly, Lewis’s principle states that if a rational agent believes some outcome to have a given chance of occurring, then her credence in that outcome is equal to that chance (so long as she has only admissible information). Lewis argued that any adequate theory of chance must explain why we ought to form our credences in accord with the Principal Principle. This has proved a difficult burden to meet, but an explanation of swamping is a step in the right direction. Elliott will argue that an agent’s rational opinions about what she calls “hypothetical explanations” swamp her other (admissible) evidence in precisely the way that an agent’s rational opinions about chances swamp her other (admissible) evidence. On her view, swamping is merely a special instance of a broader principle that relates rational opinions regarding hypothetical explanations with rational opinions regarding what they explain. This broader principle, and the explanatory role that objective chances play for rational agents, provide an explanation of swamping.  

For further information, please contact Patty Jones, or 949-824-1520.


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