 There are four historical modal paradigms in ancient philosophy: the frequency interpretation of modality, the model of possibility as a potency, the model of antecedent necessities and possibilities with respect to a certain moment of time (diachronic modalities), and the model of possibility as non-contradictoriness. None of these habits of thought, which were well known in early medieval times through the works of Boethius, was based on the idea of modality as involving reference to simultaneous alternatives. This new paradigm was introduced into Western thought in early twelfth-century discussions influenced by Augustine’s theological conception of God as acting by choice between alternative histories.