become an _argumentum ad populum_; an argument in favor of a new
park which should dwell on selfish advantages which might be gained by
the abutters without regard to larger municipal policy would probably be
an _argumentum ad hominem_.

Obviously these two forms of shifting the issue trench closely on the
element of persuasion in an argument, and in making the distinction you
must apply common sense. Your adversary may reprove you for an
_argumentum ad hominem_ or _ad populum_, when you believe that you are
keeping well within the bounds of legitimate persuasion; but in general
it is safe to guard your self-respect by drawing a broad line between
dodging and unworthy appeals to prejudice and justifiable appeals to
feeling and personal interest.

EXERCISES

1. Name a question of policy which would be settled by the establishment
of some controverted fact.

2. Find in the daily papers an account of a trial in which evidence was
declared inadmissible under the rules of law which would have been taken
into account by the average man outside the court in making up his own
mind.

3. Name three questions in which the evidence would be affected by
temperamental and other prepossessions of the witness.

4. Name a scientific question in which some important fact is
established by reasoning from other facts.

5. Cite a case, either from real life or from fiction, in which a fact
was established by circumstantial evidence; analyze the evidence and
show how it rests on reasoning from similarity.

6. Give a case in which what you believed to be direct observation of a
fact deceived you.

7. Give an example from your own experience within a week where vague
authorities have been cited as direct evidence.

8. What would you think of the writer of the following sentences as a
witness to the numbers and importance of the participants in the woman
suffrage procession he is reporting?

Fifth Avenue has seldom, if ever, been more crowded than on Saturday
afternoon, and never anywhere have I seen so many women among the
spectators of a passing pageant. Throngs, many tiers deep, flanked
the line of march, and these throngs were overwhelmingly composed of
women. As I passed from block to block I could not get away from the
thought that the vastest number of these were sick of heart and
ashamed that they, too, were not in line behind the kilted band that
headed the procession, the historic symbol