Abstract
Suppose a police car gives chase to some violent criminals, putting innocent bystanders at risk. The criminals have not threatened the police in any way; so we would not normally say that the police have been coerced into chasing. Nor are the police merely responding to natural circumstances, so they are not acting under necessity, in the usual sense. The case is different from one in which an ambulance speeds to hospital, putting innocent bystanders at risk, because the reason for the police speeding has to do with the unreasonable behaviour of others. Yet that unreasonable behaviour does not constitute threatening behaviour. How then should we describe what happened?