Contextuality and Random Variables

Abstract Contextuality is a property of systems of random variables. The identity of a random variable in a system is determined by its joint distribution with all other random variables in the same context. When context changes, a variable measuring some property is instantly replaced by another random variable measuring the same property, or instantly disappears if this property is not measured in the new context. This replacement/disappearance requires no action, signaling, or disturbance, although it does not exclude them. The difference between two random variables measuring the same property in different contexts is measured by their maximal coupling, and the system is noncontextual if one of its overall couplings has these maximal couplings as its marginals.