Intuitively, if two event mentions are related to the same set of events, it is likely that the two event mentions refer to the same real world event, even when their word forms and local contexts are distinct.
we merge event clusters if their event mentions are tightly associated (i.e., having the same dependency relations) or loosely associated (i.e., co-occurring in the same sentential context) with enough (i.e., passing a threshold) other events that are known coreferent.