II. Internal tests of evidence.
A. Is the evidence consistent (a) with itself, (b) with known facts, (c) with human experience?
B. Is it first-hand evidence?
C. Can the evidence be classed as especially valuable?
1. Does it consist of hurtful admissions?
2. Is it undesigned evidence?
3. Is it negative evidence?
III. Test of argument from authority.
A. Is the witness an acknowledged authority on the subject about which he testifies?
To overthrow or weaken argument from authority, one may either discredit its source or bring to light some inconsistency in the statement itself. Usually the former method alone is possible. To accomplish this result, one may show that the witness spoke from insufficient knowledge of the matter, or was prejudiced, or had some personal interest in the case. Counter authority will also be of assistance. The following quotation taken from a college debate furnishes the student a good example of how to handle this sort of refutation.