Temporal modality concerns the way according to which a fact originally associated with a time point or interval at a given granularity distributes itself over the corresponding time points at finer granularities or within the interval at the same level of granularity. We distinguish two basic temporal modalities, namely sometimes and always.
The sometimes temporal modality states that the relevant fact is true in at least one of the corresponding time points at the finer granularity for time points, or in at least one of the time points of the interval in case an interval is given. For instance: ``The light was on yesterday afternoon,'' meaning that it was on at least for one minute in the afternoon (assuming minute as temporal quantum).
The always temporal modality states that the relevant fact is true in each corresponding time point at the finer granularity. This is the case, for instance, of the sentence: ``The shop remained open on a Sunday in April 1990 all the day long'' with respect to the granularity of hour.
This issue is relate to attributes varying within their validity intervals.