[[A °nominal bears a force role if it serves to express the nonvolitional initiator of an event.]]
force (SEM) = a semantic role including participant roles for a participant that initiates an event but is not volitional (usually because it is not human), i.e. is not an agent. Example: in Lightning shattered the old tree, the lightning initiates the shattering event but is not an agent. (Section 6.1.2)