[Roaming through methodology. IV. Causality]

If a factor A is often followed by an event B, it may erroneously be concluded that one causes the other. Actually B may have been brought about by a factor C (the true cause), A being only an epiphenomenon of C. If factors other than C (for example D or E) can cause the same effect B, none of those factors is a necessary cause. Causes often are multiple: a single causal factor is often not sufficient for a certain effect to ensue, whereas that effect can result from a number of factors acting together (simultaneously or consecutively).