The Born rule (also called the Born law, Born's rule, or Born's law) is a law of quantum mechanics which gives the probability that a measurement on a quantum system will yield a given result. It is named after its originator, the physicist Max Born. The Born rule is one of the key principles of quantum mechanics. There have been many attempts to derive the Born rule from the other assumptions of quantum mechanics, with inconclusive results; for example, while it has been claimed that Born's law can be derived from the Many Worlds Interpretation, the proofs have been criticized as circular. However, within the Quantum Bayesianism interpretation of quantum theory, it has been shown to be an extension of the standard Law of Total Probability, which takes into account the Hilbert space dimension of the physical system involved. The Born rule can, however, be derived in the ambit of so-called Hidden-Measurements Interpretation of quantum mechanics, by averaging over all possible measurement-interactions that can take place between the quantum entity and the measuring system.