Applying the concepts of Chapter 8 raises one issue that has not come up seriously before now. In order to think precisely about how an argumentative passage works, we need to use a few technical terms, that is, words with fixed but exact meanings. The previous chapters contain their share of special vocabulary; but, especially in the case of nonargumentative persuasion and pseudoreasoning, the meanings of those terms are flexible, even elusive. The rigorous study of argument does not permit such flexibility.

Moreover, the words with such specific meanings already have common uses outside the official study of critical thinking. So we need to exercise caution not to blur the technical vocabulary with the ordinary occurrences of the same words. The colloquial meanings of the words are not false. But they belong in contexts outside logic.

Start with that word "argument" itself. In ordinary parlance the word refers to disagreement, especially a heated one. In logic it means a set of sentences by a single speaker or writer, whether or not that person disagrees with anyone else. It is true that even philosophers--who make the examination of arguments their main business--reach for combative metaphors when praising a piece of reasoning. We hear of "unbeatable" arguments, even of a "knock down, drag out" argument that no one can vanquish. But though such turns of phrase show that arguments get used in debates and disputes, in verbal battles of every stripe, you should not infer that an argument requires any contentious context.

Then the word "valid." We speak of opinions as valid; feelings too. "Your anger was perfectly valid, since you thought he'd insulted you." No confusion here and no misuse of language. But when we enter the house of logic we check this meaning of "valid" at the door and use the word only to refer to arguments with the proper internal structure.

To a lesser degree the same cautions are in order for the adjectives "sound" and "good." When engaged in clarifying and identifying arguments, do not speak of ideas, questions, or suggestions as sound. Ideas can no more be sound than numbers can be hungry, at least not when you're talking logic.

Even when restricting "sound" to arguments, watch out. All sound arguments have true conclusions, but not all arguments with true conclusions are sound. So don't call an argument sound merely as a way of affirming its conclusion, nor merely as a compliment. It is a term of praise for arguments, but only in the way that "registered nurse" and "poet laureate" are terms of praise. They mean something specific and must be earned; so too soundness.

Treating certain terms in a strict technical sense will help you avoid misunderstandings now. When we turn to logic proper--and especially the truth-functional logic of Chapter 10--such exactness will prevent outright error. Logic tends to demand unchanging and narrow definitions for its terms. We give up some flexibility, some color, some freshness of phrase; we gain the clarity and precision that are logic's contribution to thinking.