The only change that is required is the substitution of the word 'event' for the word 'duration.' Accordingly an abstractive set of events is any set of events which possesses the two properties, (i) of any two members of the set one contains the other as a part, and (ii) there is no event which is a common part of every member of the set.

Such a set, as you will remember, has the properties of the Chinese toy which is a nest of boxes, one within the other, with the difference that the toy has a smallest box, while the abstractive class has neither a smallest event nor does it converge to a limiting event which is not a member of the set.
Thus, so far as the abstractive sets of events are concerned, an abstractive set converges to nothing.

There is the set with its members growing indefinitely smaller and smaller as we proceed in thought towards the smaller end of the series; but there is no absolute minimum of any sort which is finally reached.

In fact the set is just itself and indicates nothing else in the way of events, except itself.

But each event has an intrinsic character in the way of being a situation of objects and of having parts which are situations of objects and--to state the matter more generally--in the way of being a field of the life of nature.