They give the argument the effect of being founded on a rock.  If it be obvious that the statistics have been freshly gathered, and are not merely casual and second-hand gleanings, they have still greater effect, for then they have a secondary force in testifying to the personal knowledge that the witness has of the subject.  We shall see later the danger of the fallacy of generalizing on too narrow a basis:  a generalization based on a good body of statistics runs no danger of this fallacy.

31.  The Opinion of Recognized Authorities.  The other chief source of evidence to establish a fact which consists of a large and complex state of affairs is the opinion of recognized authorities on the subject.  The strength of such evidence depends on whether the audience will accept the person you cite as having authority on the matter.  Most of us read some newspaper or periodical in the opinions of which we have confidence, because they seem to be based on investigation and competent knowledge.  The annual report of the Secretary of the Treasury is excellent evidence on the state of the national finances.  The reports of presidents of colleges are excellent evidence from authorities on such questions as the value of the elective system or the effect of raising the standard of admission.  The report of a dean or of a schoolmaster on the value of organized athletics is effective if the audience knows that he likes out-of-door sports and takes time to see the games.  Evidence drawn from an authority who is likely to be used by the other side is doubly effective, since your readers recognize that his competence is admitted.

If a man has given his life to the study of a subject and has published books that are of recognized authority, his evidence will be of especial weight.  Mr. Bryce’s opinion on all questions concerning a state of affairs in this country would be recognized at once as weighty, for he has given time and study to collecting the multitude of small facts which constitute the large fact.  His opinion that political honesty is increasing with us has brought comfort to many good citizens who had grown despondent over the accounts of recurrent rascality in the newspapers and magazines.  This is a typical case for the citation of authorities; for the facts are enormous in number, very widely scattered, and often contradictory.  Only a man who has taken the pains to keep himself constantly informed, whose judgment has been trained by long consideration and comparison of the facts, and who is born with the judicial temperament can attain the authority of Mr. Bryce.

There will be cases on which you will have the right to put yourself forward as an authority, for on many subjects which fall within the range of undergraduates their knowledge is first-hand.  On all questions of athletics, especially, an undergraduate is apt to have freshly in mind a considerable mass of facts.  In the same way, on the results of certain requirements for admission to college, you can speak from recent experience.  In matters concerning your own city, too, you may have original knowledge.