Principle of Indifference - Principle of Insufficient Reasoning

• is a rule for assigning epistemic probabilities
• this principle is at the heart of the classical inference

Principle of Indifference - Statement

• The principle of indifference states that 2 outcomes should have the same probability if they’re symmetric with respect to the factors that cause them
• The principle of indifference states that in the absence of any relevant evidence, agents should distribute their credence (or 'degrees of belief') equally among all the possible outcomes under consideration

Principle of Indifference - Relation to Other

• In Bayesian probability, the principle of indifference is the simplest non-informative prior
• In Frequentist probability, the principle of indifference is meaningless. Probabilities are relative frequencies rather than degrees of belief in uncertain propositions, conditional upon state information

Principle of Indifference - Example

In the die-rolling example, all 6 outcomes are symmetric because the only difference between them is in the side labels. Labels don’t physically affect the process in any way. So, any argument you can give for why a particular outcome is more likely than the others can also be used to argue for any of the other outcomes.