One reason why causation interests us is because it is related to the important issue of human agency. When we act, we cause things to happen. We are the originators of new causal chains, or so we would like to think. Causation is not merely a theoretical problem, which concerns only philosophers; nor is it important just because some distant discipline depends on it. Rather, if human agency is causation, then the issue is one of immediate significance to every being who has ever done anything.