Acccuracy, Risk, and the Principle of Indifference

Prof Richard Pettigrew (University of Bristol (UK))

Richard Pettigrew, Reader in the Department of Philosophy at the University
of Bristol

Title: Accuracy, Risk, and the Principle of Indifference

Abstract:  In Bayesian epistemology, the problem of the priors is this:  How
should we set our credences (or degrees of belief) in the absence of
evidence?  The Principle of Indifference gives a very restrictive answer.
It demands that an agent with no evidence divide her credences equally over
all possibilities.  That is, she ought to adopt the uniform distribution.
In this paper, I offer a novel argument for the Principle of Indifference.
I call it the Argument from Accuracy.  It shares much in common with Jim
Joyce's ''nonpragmatic vindication of probabilism'' (Joyce 1998).  Joyce
showed that, for a broad range of accuracy measures, if an agent's credences
do not satisfy the axioms of probability, then there are credences that do
satisfy those axioms that are guaranteed to be more accurate.  In my
argument, I show that if an agent's credence do not satisfy the Principle of
Indifference, then, for a similarly broad range of accuracy measures, they
risk greater inaccuracy than they need to.

The talk is at 5.15 pm in the seminar room on the second floor of the
Lakatos building at the London School of Economics. All welcome!