  Apart from that, Diodorus' modalities are of a very different kind from Philo's. There is no modal expression hidden anywhere in his accounts. Instead, which Diodorean modality a proposition has depends wholly on the range of truth-values it has at present and in the future. For example, if a proposition is always true from now on, it is now both necessary and possible; if it is, from now on, sometimes true but not always, it is possible, but not necessary. Hence it is not the case — as is sometimes assumed — that for Diodorus, every proposition is either necessary (and possible) or impossible (and non-necessary). There are propositions that are contingent in the sense of being both possible and non-necessary, namely all those which will change their truth-value at some future time. The proposition ‘It is day’ is such a case.