How to tell the difference between just argument and causation weakening questions

Could someone clarify the best way to tell the difference between weakening questions where the argument is a simple argument and where the argument involves causation? Is it that the causation argument involves a change in a phenomenon? Does this always hold true? I guess anyway that in each instance, you are still attacking the "support," as providing an alternative explanation for a causation is not attacking the hypothesis or phenomenon, but it would still be helpful to know when to pull out my causation logic skills.