 A second set of worries has to do with the application of the CM model to systems which depart in various respects from simple physical paradigms such as the collision described above. There are a number of examples of such systems. First, there are theories like Newtonian gravitational theory which involve “action at a distance” in a physically interesting sense. Second, there are a number of examples from the literature on causation that do not involve physically interesting forms of action at a distance but which arguably involve causal interactions without intervening spatio-temporally continuous processes or transfer of energy and momentum from cause to effect. These include cases of causation by omission and causation by “double prevention” or  “disconnection.”[6]  In all these cases, a literal application of the CM model seems to yield the judgment that no explanation has been provided—that Newtonian gravitational theory is unexplanatory and so on. Many philosophers have been reluctant to accept this assessment.