Events and action can happen or occur. They often have fairly definite temporal but indefinite spatial limits. A given event or action is only partially present at a given time, for example the French Revolution was not wholly present at the moment of the Tennis Court Oath. A part of an event or action can constitute an independent event or action at a given time. Unlike objects, entities in this class often have causal relationships. Several events or actions can occur simultaneously at the same spatial point. Entities that participate in events and actions are called objects.