 4. With regard to liability for “double preventions” (where, for example, a defendant prevents a lifeguard from preventing another from drowning), usually there is a supposedly cause-based liability for the unprevented harm in such cases because a defendant preventing a preventer from preventing some harm is regarded as the cause of that harm. Yet sometimes (for double preventions amounting to the “allowings” as conceived by the centuries-old doing/allowing distinction) double preventions are treated just like omissions so that there is no legal causation and no liability except for those exceptional circumstances (the status, undertaking, and causing of peril exceptions) that exist for omission liability (Moore 2009a: 61–65, 459–460).