 Boethius developed the diachronic ideas as part of his criticism of Stoic determinism. If it is not true that everything is causally necessitated, there must be genuine alternatives in the course of events. Free choice was the source of contingency in which Boethius was mainly interested, but he thought in addition that according to the Peripatetic doctrine there is a real factor of indeterminacy in the causal nexus of nature. When Boethius refers to chance, free choice, and possibility in this context, his examples include temporalized modal notions which refer to diachronic prospective possibilities at a given moment of time. A temporally determinate prospective possibility may not be realized at the time to which it refers, in which case it ceases to be a possibility. Boethius did not develop the idea of simultaneous alternatives which would remain intact even when diachronic possibilities had vanished, insisting that only what is actual at a certain time is at that time possible at that time (cf. (3) above). But he also thought that there are objective singular contingencies, so that the result of some prospective possibilities is indefinite and uncertain ‘not only to us who are ignorant, but to nature’ (In Periherm. I, 106, 120; II, 190–192, 197–198, 203, 207). (For Boethius’s modal conceptions, see Kretzmann 1985; Knuuttila 1993, 45–62.)