A “universal” prior is a probability distribution that assigns positive probability to every thinkable hypothesis, for some reasonable meaning of “every thinkable hypothesis”. A central example would be Solomonoff induction, in which the observations are a sequence of bits, the universal prior is “every possible computer program that generates bit sequences”, and every such computer program starts with a positive probability.
- Inductive prior
Some states of pre-observation belief can learn quickly; others never learn anything. An “inductive prior” is of the former type.