Cause to Effect.  Just as the explainer may pass from cause to effect so may the arguer.  Other names for this method are antecedent probability and a priori argument.  In argument from a known cause an effect is proven as having occurred or as likely to occur.  In solving crime this is the method which uses the value of the motives for crime as known to exist in the feelings or sentiments of a certain accused person.  A person trying to secure the passage of a certain law will prove that it as the cause will produce certain effects which make it desirable.  Changed conditions in the United States will be brought forward as the cause to prove that the Federal government must do things never contemplated by the framers of the Constitution.  Great military organization as the cause of the recent war is used now in argument to carry on the plea for the securing of peace by disarmament.

The main difficulty in reasoning from cause to effect is to make the relationship so clear and so close that one thing will be accepted by everybody as the undisputed cause of the alleged effect.

Effect to Cause.  In reasoning from effect to cause the reverse method is employed.  This is also termed argument from sign or the a posteriori method.  In it, from some known effect the reasoning proves that it is the result of a certain specified cause.  Statistics indicating business prosperity might be used as the effect from which the arguer proves that they are caused by a high protective tariff.  A speaker shows the good effects upon people to prove that certain laws—­claimed as the causes—­should be extended in application.  Arguments from effect to cause may be extremely far reaching; as every effect leads to some cause, which is itself the effect of some other cause, and so on almost to infinity.  The good speaker will use just those basic causes which prove his proposition—­no more.

In actual practice the two forms of reasoning from cause to effect and from effect to cause are frequently combined to make the arguments all the more convincing.  Grouped together they are termed causal relations.

Persuasion.  When a speaker has conclusively proven what he has stated in his proposition, is his speech ended?  In some cases, yes; in many cases, no.  Mere proof appeals to the intellect only; it settles matters perhaps, but leaves the hearer cold and humanly inactive.  He may feel like saying, “Well, even if what you say is true, what are you going to do about it?” Mathematical and scientific proofs exist for mere information, but most arguments delivered before audiences have a purpose.  They try to make people do something.  A group of people should be aroused to some determination of purposeful thought if not to a registered act at the time.  In days of great stress the appeal to action brought the immediate response in military enlistments; in enrollment for war work; in pledges of service; in signing membership blanks and subscription blanks; in spontaneous giving.