What is Argument?

Legal Definition
In philosophy and logic, an argument is a series of statements typically used to persuade someone of something or to present reasons for accepting a conclusion. The general form of an argument in a natural language is that of premises (typically in the form of propositions, statements or sentences) in support of a claim: the conclusion. The structure of some arguments can also be set out in a formal language, and formally defined "arguments" can be made independently of natural language arguments, as in math, logic, and computer science.

In a typical deductive argument, the premises guarantee the truth of the conclusion, while in an inductive argument, they are thought to provide reasons supporting the conclusion's probable truth. The standards for evaluating non-deductive arguments may rest on different or additional criteria than truth, for example, the persuasiveness of so-called "indispensability claims" in transcendental arguments, the quality of hypotheses in retroduction, or even the disclosure of new possibilities for thinking and acting.

The standards and criteria used in evaluating arguments and their forms of reasoning are studied in logic. Ways of formulating arguments effectively are studied in rhetoric (see also: argumentation theory). An argument in a formal language shows the logical form of the symbolically represented or natural language arguments obtained by its interpretations.
-- Wikipedia
Legal Definition
Practice. Cicero defines it ii probable reason proposed in order to induce belief. Ratio probabilis et idonea ad faciendam fidem. The logicians define it more scientifically to be a means, which by its connexion between two extremes) establishes a relation between them. This subject belongs rather to rhetoric and logio than to law.
-- Bouviers Law Dictionary
Legal Definition
In rhetoric and logic, an inference drawn from premises, the truth of which is indisputable or at least highly probable. The argument of a demurrer, special case, appeal, or other proceeding involving a question of law, consists of the speeches of the opposed counsel; namely, the "opening" of the counsel having the right to begin, (q. v.il the speech of his opponent, and the "reply" of the first counsel. It answers to the trial of a question of fact. Sweet. But the submission of printed briefs may technically constitute an argument. Malcomb v. Hamill, 65 How. Prae. (N. Y.) 506; State v. California Min. Co.., 13 Nev. 209.
-- Black's Law Dictionary