Between Potentiality and Actuality: Probability as Structural Openness

This paper proposes a novel interpretation of probability, locating it neither solely in epistemic belief nor in empirical frequency, but in the structural openness of situations prior to actualization. Drawing on the classical distinction between potentiality and actuality, the paper argues that probability expresses the structural condition under which multiple outcomes remain possible before one becomes actual. The structural openness interpretation is distinguished from Bayesian, frequentist, propensity, and logical accounts, and a formal Structural Openness Principle is advanced. The paper further explores a quantum-like analogy to illustrate how probability reflects indeterminacy prior to determination, while maintaining philosophical independence from quantum physics. A concrete worked example demonstrates the interpretive advantage of the structural openness account for singular, non-repeatable events. Objections from epistemic, ontological, formalist, and pluralist perspectives are addressed. The proposed interpretation offers a unified account that resolves persistent difficulties in the philosophy of probability, particularly regarding singular events, the reference class problem, and the relationship between probability and becoming.