Term brought into currency by C. B. Martin, and the Australian philosopher David Armstrong. The idea is that propositions cannot be ‘barely’ true. There must be something making them true: a fact, or substantial complex or state of affairs. The principle motivates substantial metaphysical and ontological searches for the ultimate nature of such complexes. It also gives rise to certain problems: for instance, what is the truthmaker for ‘unicorns do not exist’?