Causal connections can be observed. We see events bringing about other events whenever things interact with one another. Seeing that two events are causally connected is nevertheless possible only relative to a rich background of causal knowledge. Causal knowledge, however, rests only partly on our apathetic observation of generically identical situations. It is mainly gained by active intervention into these situations and by manipulation of the processes in question. So knowledge of causality is achieved on the basis of two different kinds of observations: 1) whether events of the same sort as the actual events manifest the same invariant connection under circumstances that are generically different as well as similar to the actual circumstances; and 2) how the consequences become different in situations in which these types of events individually are subjected to control and intervention.