What is an argument?
An argument is a group of statements (or propositions) in which the truth of one statement, the conclusion, is claimed to follow from the assumed truth of the other(s), the premises. In colloquial American English, the word "argument" has much broader signification, often being used as a synonym for a "disgreement" or a "dispute." The word can also carry the suggestion of a "verbal altercation" or a "shouting contest." None of these uses is intended in the context of the study of logic. Logic, properly speaking, may be said to be concerned with that subclass of "arguments," which are perhaps most accurately called "rational arguments."
Because "arguments" are defined in terms of "statements" or "propositions," and because "statements" or "propositions" are conveyed by "language," it follows that arguments must be such that they can be given linguistic expression. Since logic is concerned with the study of arguments, logic is concerned with what can be stated in a language. That which cannot be expressed in a language lies outside the bounds of logic.
An argument is not merely any group of statements. It must exhibit a flow of thought from the reasons given in the premises to the truth of the conclusion. Notice that every argument claims that its conclusion "follows" from its premises, or in other words the premises -if they are in fact true- provide good grounds or reasons for the truth of the conclusion. However, while all arguments make this claim, all such claims are not equally justified; that is, not all arguments are equally "good" arguments. Some arguments are better than others, and some, of course, are altogether "bad."
Arguments are often used to persuade people to believe (or not believe) the truth of various claims; however, the study of techniques of persuasion is "rhetoric," not "logic." Rhetoric must inevitably involve considerations of psychological and social matters, for different persons and different cultures will differ in what they consider persuasive. Logic has no direct concern with such questions that lead to the formation of belief, but is concerned only with the argument itself, not with those who use it or who may, or may not, find it persuasive. Obviously logic may be used as a device for persuasion, and one might hope that one would find good logical arguments persuasive. Nevertheless, it is easy to imagine situations in which purely logical considerations carry little persuasive force, and in which logically irrelevant considerations can be very psychologically persuasive.