ARGUMENTATION is the process of proving or attempting to prove a given proposi tion the truth of which is doubtful or disputed. It is, in many respects, the converse of the proc ess of inference which is reasoning from premises to a conclusion. In arguing, the con clusion becomes a thesis and the facts or premises from which it was inferred become the reasons by which it is proved. Inference is a forward movement from the premises to the conclusion; arguing is a backward movement, or reference, from the thesis to the grounds which support it. Inference is the process by which we ourselves reach a conclusion or be lief ; arguing is the process by which we seek to induce belief in others.
Proof requires that the proposition to be proved be brought within the scope of an ac cepted law or principle, a law or principle be ing defined as every general proposition that includes, or may be applied to, unascertained cases. This may be done by setting forth evi dence, that is, facts observed by those sought to be convinced, or established to their satis faction, which show the relation between the two. In practice argumentation is usually elliptical. The whole of the proof is seldom stated in full. The advocate is usually content to state one or more facts, leaving it to those addressed to supply the presuppositions in the light of which alone such facts may be in terpreted. Implications which may be readily supplied are usually omitted. Thus, if it be argued that "Congress is in session" for the reason that "the flag is flying over the Capitol," it is clear that the assertor relies not only on the fact given as a reason but also on an implied assumption which may be expressed as a gen eral proposition: "Whenever the flag is flying over the Capitol, Congress is in session." Every valid argument, then, when fully expressed, con sists of a proposition to be proved which may be called the Thesis, and two proving proposi tions usually called the reasons or the proof, one of which is a general proposition and may be called the Principle, and the other is a state ment of evidence and may be called for distinc tion the Reason, and shows that the thesis is brought within the scope of the principle. A
thesis is said to be proved: (1) if the reason and the principle are known or admitted to be true, and (2) if the thesis is contained, involved or implied in them. An argument may be com pared to a lever; the thesis is the weight to be lifted, the principle is the fulcrum and the rea son, the power. The first requirement of proof has reference to those sought to be convinced. The advocate must found his thesis on some thing which they recognize to be true. If the reason or principle be not accepted, the proof remains incomplete until the disputed proposi tion is itself proved by reference to another reason and principle, and so on until some holding ground is reached, some reason and principle which will be unchallenged. The sec ond requirement is concerned with the rela tion of the thesis to the other propositions of the argument. If the principle and the reason are both expressed, the question whether or not they imply the thesis is manifest in most cases on simple inspection.
Proof may be either conclusive or probable, To prove a proposition means strictly to estab lish its truth conclusively and beyond all doubt. In practice, however, a proposition is said to be proved when its truth is shown to be probable or highly probable, or so probable that we do not hesitate to act as if it were true. Thus, in a criminal trial a prisoner's guilt is said to be proved if it be established beyond a reasonable doubt ; and in a civil trial the plaintiff's case is said to be proved if there is a mere preponder ance of evidence in its favor. There are many principles that cannot be asserted or accepted as true universally, but only generally, or in most cases, and when such a principle is relied on as the foundation of an argument the thesis can only be asserted as probably true. So if the reason can only be asserted as probable, the thesis can have no higher certainty. In most cases it is only possible to establish a disputed question with more or less probability, to afford a presumption of its truth, and to shift the bur den of proof on him who maintains the con trary.