Resurrecting Logical Probability

The logical interpretation of probability, or ``objective Bayesianism'– the theory that (some) probabilitiesare strictly logical degrees of partial implication – is defended.The main argument against it is that it requires the assignment ofprior probabilities, and that any attempt to determine them by symmetryvia a ``principle of insufficient reason' inevitably leads to paradox.Three replies are advanced: that priors are imprecise or of little weight, sothat disagreement about them does not matter, within limits; thatit is possible to distinguish reasonable from unreasonable priorson logical grounds; and that in real cases disagreement about priorscan usually be explained by differences in the background information.It is argued also that proponents of alternative conceptions ofprobability, such as frequentists, Bayesians and Popperians, areunable to avoid committing themselves to the basic principles oflogical probability.