 In discussing future contingent statements in In Chapter 9 of De interpretatione, Aristotle says that what is, necessarily is when it is, but he then qualifies this necessity of the present with the remark that it does not follow that what is actual is necessary without qualification. If he meant that the temporal necessity of a present event does not imply that such an event necessarily takes place in circumstances of that type, this is an unsatisfactory ‘statistical’ attempt to avoid the problem that changeability as a criterion of contingency makes all temporally definite singular events necessary (Hintikka 1973). Another interpretation is that Aristotle wanted to show that the necessity of an event at a certain time does not imply that it would have been antecedently necessary. Aristotle discusses such singular diachronic modalities in some places (Met. VI.3; EN III.5, 1114a17–21; De int. 19a13–17) in which he seems to assume that the conditions which at t1 are necessary for p to obtain at a later time t2 are not necessarily sufficient for this, although they might be sufficient for the possibility (at t1) that p obtains at t2. Aristotle did not elaborate these ideas, which might have been his most promising attempt to formulate a theory of unrealized singular possibilities (for example  De int. 19a12–14. The importance of this model is particularly stressed in Waterlow 1982a; see also von Wright 1984; Weidemann 1986; Gaskin 1995.