The theory and practice of argumentation and debate

by Victor Alvin Ketcham

5. Each card should be complete in itself.

6. Material for refutation should be preceded at the top of the card by an exact statement of the argument to be refuted.

7. The main issues or subjects to which the evidence relates should be stated at the top of the card.

8. The source from which the evidence is taken should be definitely stated at the bottom of the card.

III. Selecting evidence.

All the reliable evidence obtainable should be collected before the selection of the exact evidence which is to go into the argument is begun. If the student has confined his collecting to the sources of evidence suggested in the first section of this chapter, the presumption will be in favor of its reliability. This presumption may be strengthened and in some instances turned into certainty by a selection made in accordance with the rules which it is the object of this section to present.

It is of the utmost importance that a large amount of evidence from which to construct the brief and argument be available. It is only in this way that the strongest evidence obtainable can be brought to the support of the argument. All the evidence used must be relevant but not all the evidence that is relevant need be used. The following rules should be observed in the selection of evidence:

1. The evidence must come from the most reliable source to which it can be traced.

All the evidence collected must have back of it some reliable source, as indicated in the discussion of Sources of Authority. The more trustworthy this source the more valuable is the evidence and the greater the weight given to it. Therefore “the evidence must come from the most reliable source to which it can be traced.” Every fact offered in evidence comes from some definite source. If this source cannot be found the fact should be discarded as worthless. To illustrate, in the investigation of a subject, a fellow-student may know some fact which is a most important piece of evidence in your favor. He may tell you about this fact, but you would not think of going into the debate and quoting one of your fellow-students as authority. Therefore you will at once ask the student from what source he obtained knowledge of the fact. He may reply that he has seen it in a newspaper article. But since a newspaper is usually of little value as an authority, you cannot rely upon its statement. Therefore you inquire from what source the newspaper obtained it. By consulting the newspaper it is found that the statement is made in an editorial which comments upon an article found in the North American Review. You must then consult the number of the North American Review to which reference is made. This is fairly reliable, and anyone would feel justified in quoting it as the source of his evidence, although he would not feel justified in quoting the statement of a fellow-student or the statement of a newspaper.

If the statement is one which is an opinion of the editor of the North American Review, or if for any other reason it cannot be traced back of this source, North American Review, volume and page, should be quoted as the source of the evidence. But suppose that the statement can be traced to its original source. To be more concrete, let us assume that the statement is to the effect that there is a surplus of over one million dollars in the United States treasury. For such a statement the North American Review is not the most reliable source. In this case the most reliable source is the Report of the Treasurer of the United States, which can be found in almost any library. When this fact is located the student should make an exact statement of the amount of the surplus and refer to the Report of the United States Treasurer.