Causes and effects. Showing that one event is the cause or the effect of another can help support an argument. Suppose you are trying to explain, in a petition to change your grade in a course, why you were unable to take the final examination. You would probably trace the causes of your failure to appear—your illness or the theft of your car, perhaps—so that the committee reading the petition would reconsider the effect—your not taking the examination.

Tracing causes often lays the groundwork for an argument, particularly if the effect of the causes is one we would like to change. In an environmental science class, for example, a student may argue that a national law regulating smokestack emissions from utility plants is needed because (1) acid rain on the East Coast originates from emissions at utility plants located in the Midwest, (2) acid rain kills trees and other vegetation, (3) utility lobbyists have prevented midwestern states from passing strict laws controlling emissions from such plants, and (4) if such laws are not passed, acid rain will eventually destroy most eastern forests. In this case, the fourth point ties all of the previous points together to provide an overall argument from effect: if X, then Y.