Abstract: The general claims of this paper are as follows. As a result of chaotic dynamics we can usually not know what the deterministic causes of events are. There will, however, be invariant forwards transition chances from earlier types of events, which we typically call the causes, to later types of events, which we typically call the effects. There will be no invariant backwards transition chances between these types of events. This asymmetry has the same origin and explanation as the arrow of time of thermodynamics.