The most conspicuous feature of any past event is its apparent unreality. A past event does not exist now; it has vanished, passed away, disappeared; it is not present any longer. The alleged unreality of the past is probably the reason why the past itself is rarely an object of systematic philosophical inquiry. Its only feature seems to be a negative one: "to have ceased to exist" or "to have passed out of existence." What else can be said about it? There seems hardly any problem here at all.