William Trufant Foster on Debate and DefinitionArgumentation and Debating (Houghton Mifflin Co.: 1908), pp. 145-6.
We have seen that the first step in argument is the interpretation of the proposition in order to resolve it into its essential parts; and we have seen that a first step in any such interpretation must be the definition of terms. Many fallacies are due to inadequate definition of terms, for the most dangerous source of verbal confusion and consequent dispute is our failure to set forth our meaning with perfect clearness, and the more subtle the misinterpretation, the greater the danger. The study and practice of argumentation is sure to reveal innumerable chances for confusion due to the lack of satisfactory definitions. We can seldom proceed far in any argument, no matter how simple it may seem to be, without feeling the necessity for this preliminary work of exposition. Without the protection of painstaking definitions, no point in an argument is proof against the insidious fallacies of ambiguity. When the two sides in a controversy use the same terms with different meanings or different terms with the same meaning; when colleagues are not agreed and consistent in the use of terms; when any man employs a term in one sense and later shifts to another sense, the result is a confusion which may carry in its train whole troops of fallacies. Clear and convincing definitions are fundamental requisites of sound argument.