If Sophia is ignorant about the color of a marble, the Principle of Indifference requires her to assign equal probability to each color in the partition.

Subjective probability theory models ignorance with respect to a proposition \(A\) by assigning probability of .5 to \(A\) and its complement \(\neg A\). More generally, an agent with subjective probability Pr is said to be ignorant with respect to the partition \(\{A_{1},\ldots,A_{n}\}\) if and only if \(\Pr(A_{i}) = 1/n\). The Principle of Indifference requires a doxastic agent to distribute her subjective probabilities in this fashion whenever, roughly, the agent lacks evidence of the relevan