Before revision: (the other being the Self-Indication Assumption (SIA)), states that: All other things equal, an observer should reason as if they are randomly selected from the set of all actually existent observers (past, present and future) in their reference class.
After revision: (the other being the self-indication assumption (SIA)), states that: All other things equal, an observer should reason as if they are randomly selected from the set of all actually existent observers (past, present and future) in their reference class.