Comparison.  Unfamiliar matter may be made plain by showing how it resembles something already clearly understood by the audience.  This is comparison.  It shows how two things are alike.  The old geographies used to state that the earth is an oblate spheroid, then explain that term by comparison with an orange, pointing out the essential flattening at the poles.  In any use of comparison the resemblance must be real, not assumed.  Many a speaker has been severely criticized for his facts because he asserted in comparison similarities that did not exist.

Contrast.  When the differences between two things are carefully enumerated the process is termed contrast.  This is often used in combination with comparison, for no two things are exactly alike.  They may resemble each other in nearly all respects, so comparison is possible and helpful up to a certain limit.  To give an exact idea of the remainder the differences must be pointed out; that requires contrast.

In contrast the opposing balance of details does not have to depend necessarily on a standard familiar to the audience.  It may be an arrangement of opposite aspects of the same thing to bring out more vividly the understanding.  In his History of the English People, Green explains the character of Queen Elizabeth by showing the contrasted elements she inherited from her mother, Anne Boleyn, and her father, Henry VIII.  Such a method results not only in added clearness, but also in emphasis.  The plan may call for half a paragraph on one side, the second half on the other; or it may cover two paragraphs or sections; or it may alternate with every detail—­an affirmative balanced by a negative, followed at once by another pair of affirmative and negative, or statement and contrast, and so on until the end.  The speaker must consider such possibilities of contrast, plan for his own, and indicate it in his brief.

Nearly any speech will provide illustrations of the methods of comparison and contrast.  Burke’s Conciliation with America has several passages of each.

Cause to Effect.  Explanations based on progressions from cause to effect and the reverse are admirably suited to operations, movements, changes, conditions, elections.  An exposition of a manufacturing process might move from cause to effect.  A legislator trying to secure the passage of a measure might explain its operation by beginning with the law (the cause) and tracing its results (the effect).  So, too, a reformer might plead for a changed condition by following the same method.  A speaker dealing with history or biography might use this same plan.