What lets causation be more or less effective is the fact that three of its major connotations entail links between cause and effect which come by degrees. The links are those of being evidence for something, of explaining it and of being a means to it. A cause C may be linked to an effect E in each of these ways to a greater or lesser extent: it may be stronger or weaker evidence for E, explain E more or less well and be a more or less useful means to E. These three links have moreover a common measure, which is thus a natural measure of how effectively C causes E.