Authority
When authority is cited to prove a statement it must be subjected to the same tests in argument as in explanation. Is the authority reliable? Is he unprejudiced? Does his testimony fit in with the circumstances under consideration? Will his statements convince a person likely to be on the opposing side?
Why has so much so-called authoritative information concerning conditions in Europe been so discounted? Is it not because the reporters are likely to be prejudiced and because while what they say may be true of certain places and conditions it does not apply to all the points under discussion? The speaker who wants the support of authority will test it as carefully as though its influence is to be used against him—as indeed, it frequently is.