Causation is defined as a relation between facts: C causes E if and only if C and E are nomologically independent facts and C is a necessary part of a nomologically sufficient condition for E. The analysis is applied to problems of overdetermination, preemption, trumping, intransitivity, switching, and double prevention. Preventing and allowing are defined and distinguished from causing. The analysis explains the direction of causation in terms of the logical form of dynamic laws. Even in a universe that is (...) deterministic in both temporal directions, not every fact must have a cause and present facts may have no future causes. (shrink)