Definitions of Basic Terms: An argument is a set of statements one of which is being argued for on the basis of the others, those others therefore being describable as the statements being argued from. To argue for a statement is to present reasons for thinking that it is true; to argue from one or more statements is to present them as reasons for thinking that another statement is true. (Note: the word "argument' has a number of different meanings. Here what we are talking about is good or bad pieces of reasoning, not arguments in the sense of quarrels or fights. ) The conclusion of an argument is the statement being argued for.
(By convention, arguments are thought of as containing just one conclusion each, and note: in oral or written presentations of arguments, the conclusions are not necessarily presented at the end. ) The premises of an argument are the statements being argued from. (Arguments can have any number of premises. It's often assumed that every argument has to have exactly two premises, but this is false. Arguments can also have unstated premises; arguments with unstated premises are called enthymeme's. ) Definitions of Evaluative Terms: A lousy (or crummy) argument is an argument that is such that even if its premises are true, its conclusion is no more likely to be true than false.
(Lousy arguments admit of various degrees of lousiness. The extreme cases are arguments such that if their premises are true, their conclusions have to be false. ) An inductive argument (or an argument of at least some inductive strength) is an argument that is such that if its premises are true, then its conclusion is more likely to be true than false, although it could, at least conceivably, be false. (Inductive arguments admit of various degrees of strength. An inductive argument is a strong one if the truth of its premises makes the truth of its conclusion very likely. But note: even the strongest inductive argument can have true premises and a false conclusion.
) A valid argument is an argument that is such that if its premises are true, its conclusion has to be true. The conclusion of a valid argument is said to be entailed by the premises, or to follow from them, or to be deducible from them, or to be a logical consequence of them. (While a valid argument can have a false conclusion, one or more of its premises must be false if it does. In other words: no valid argument can have a false conclusion if all its premises are true. The term "deductive argument' is often used to refer to arguments the conclusions of which are supposed to be deducible from their premises whether or not they actually are, and if we use it thus, we can obviously speak of both valid and invalid deductive arguments. The term "inductive argument' can be used analogously, but arguments that are inductive in the sense defined above are never valid.
) A sound argument is a valid argument all of the premises of which are true. (It follows from the definition of a valid argument given above that a sound argument cannot have a false conclusion. ) An argument is a good argument in the strict sense of the term just in case it is either (a) a strong inductive argument with true premises or (b) a sound argument the conclusion of which isn't included among the premises and the validity of which isn't merely a function of its conclusion's being a statement that couldn't conceivably be false. (Note 1: the point of the first qualification in (b) is that circular pieces of reasoning shouldn't qualify as good arguments (even though they are valid), and the point of the second is that we " re equally far from having a good argument in any such ridiculous "proof' of a mathematical or logical truth as, say, "Grass is green, hence 2 + 2 = 4″ or "Whales aren't fish, so Plato was a philosopher unless he wasn't.' Note 2: valid arguments and strong inductive arguments are sometimes called "good arguments' even though they have false premises simply to indicate that the inferences they embody can't be faulted on logical grounds alone. Maybe we should say that such arguments are good arguments in a loose sense of the term. Nothing can be faulted about the reasoning in such arguments.
) A rationally compelling argument is a good argument in the strict sense of the term all of the premises of which are known to be true and for the falsity of the conclusion of which there is no argument that is equally good. Some hold that the term "proof's hold be reserved for those rationally compelling sound arguments the premises of which are indubitable, but the term "proof' certainly does have other uses. The fact is that the various disciplines and enterprises in which there is talk of proof typically have canons of proof all their own. A mathematical proof is one sort of thing; proof of innocence in a court of law is something else altogether. A rhetorically effective argument is an argument that succeeds, at least typically, in persuading those to whom it is presented of the truth of its conclusion.
(It is perfectly possible for a rhetorically effective argument to be a lousy argument, and it's possible for good arguments — even proofs — to fail to be rhetorically effective. ) Argument Assessment Strategy: To evaluate arguments, one first has to be able to identify them. There's no mechanical procedure for doing this, but the presence of such expressions as "since,' "for,' and "because' (which often serve to mark premises) and "therefore,' "consequently,' "hence,' and "it follows that' (which often serve to indicate conclusions) frequently serves to signal the presence of an argument. It may also help to consider such questions as these: "What, if anything, is the writer or speaker trying to establish? What, if anything, is he or she trying to prove? What's his or her thesis? What's the view he or she is defending?' If you can find an answer to such a question in relation to any given passage or set of remarks, you " ll typically have spotted a conclusion — and, you " ll recall, the statements containing the writer's or speaker's reasons for thinking that the conclusion is true are the premises.
(But don't forget: there may be unstated premises to reckon with, and in both written and oral presentations of arguments, one may encounter statements that aren't premises because they aren't parts of the argument at all).