The methods described so far involve possible causes and effects which are either present or absent in a given scenario. Mill also recognized that many phenomena vary over time by degree, rather than being either present or absent. (In the language of variables and values, Mill acknowledged that many variables have more than the two values of (fully) present and (fully) absent.) When one possible cause but not others varies along with the effect, the method of concomitant variation suggests that there is a connection