Changing the Subject
The person presenting an argument is attacked instead of the argument itself. This takes many forms. For example, the person's character, nationality or religion may be attacked. Alternatively, it may be pointed out that a person stands to gain from a favorable outcome. Or, finally, a person may be attacked by association, or by the company he keeps. There are three major forms of Attacking the Person: 1) ad hominem (abusive): instead of attacking an assertion, the argument attacks the person who made the assertion. 2) ad hominem (circumstantial): instead of attacking an assertion the author points to the relationship between the person making the assertion and the person's circumstances. 3) ad hominem (tu quoque): this form of attack on the person notes that a person does not practice what he preaches, in effect, "look who's talking".
While often it is appropriate to cite an authority to support a point, sometimes it is not. An appeal to authority is problematic if: 1) The person is not qualified to have an expert opinion on the subject; 2) Experts in the field disagree on this issue; 3) The authority was making a joke, drunk, or otherwise not being serious. 4) The authority cited is either misinterpreted or in fact did not even say what is attributed to them. 5) A fifth variation on this fallacy, "circular citation", is when a source is cited, but the cited source itself does not reference the study or authoritative source that supports the claim being made. Sometimes a whole slew of articles and books will crop up, all citing each other or some common source, but the seminal source itself fails to substantiate the claim with direct evidence or a trustworthy authority. An urban legend is born. » Also see Anonymous Authorities for a related strand of problematic appeals to authority.
The authority in question is not named, or in written arguments, their is an absence of citation. When an authority is not named, it is impossible to confirm that the authority is in fact authoritative, or even whether the claim is backed by an authority at all. As "they" say, 62% of statistics are made up on the spot. (Wink. Wink.) Furthermore, if the claim is rooted in an authoritative source, one cannot check to see whether the unnamed authority's argument should be disputed. A special case of this fallacy is the appeal to rumor or hearsay. Because the source of a rumor is typically not known, it is not possible to determine whether to believe the rumor. And this is especially important because often false and harmful rumors are deliberately started in order to discredit an opponent. » Also see Appeal to Authority for additional pitfalls.
To qualify as a fallacy of this sort, an argument is rejected explicitly because its proponent is lacking in style and grace. "He was such a jerk. I couldn't believe anything he said." In this case we have a fallacy of irrelevance. The truth needn't be pretty. As Edward R. Murrow observed, "Most truths are so naked that people feel sorry for them and cover them up, at least a little bit." Most often, the persuasive power of style acts subtly, even subconsciously. A debater who is stumbling over his words, unorganized, unsure of himself, and "uuhming" repeatedly will struggle mightily to earn a fair hearing for his argument against an opponent whose words proceed effortlessly and mellifluously. A written argument filled with typos and grammatical errors loses credibility even if the argument, given a chance, is sound. Often we grant implicit trust to a source who is attractive and seems to "have it together". In such cases, great style, or the lack thereof, has the effect of predisposing us one way or the other to an argument that should be judged on its own merits.