Propensity Theory proposes a foundational root theory encompassing quantum mechanics within a unified deductive framework. Starting from propensity as a fundamental ontological category, the theory explains all phenomena through a five-stage cycle of bond formation and dissolution. Numerical simulations across six quantum phenomena show agreement with established predictions. The theory also introduces Propensity Induction — a methodology for actively designing phenomena. Includes Author's Clarifying Notes on pluralistic realism and the genesis of information.