In an argument, much can go wrong.
Evidence may be too weak to support a position, for instance, or at times some audience members may simply reject evidence regardless of its veracity. In argument as well as in other forms of discourse, listener and reader attitudes, values, and beliefs affect acceptance of messages. So does credibility, the amount and kind of authority and character the audience perceives the speaker to possess. The more credible an audience finds a speaker, the more likely its members are to believe his or her argument.
But things can also go wrong if the argument itself isn't logical. One that contains flawed reasoning in causality, for instance, leaves logic behind and enters the realm of fallacy. So, too, does one that diverts attention from the issue to matters that are irrelevant.
Such a distraction is the red herring fallacy, a ploy that allegedly got its name from the practice of dragging a smoked fish across the path of a hunted animal in order to put the hounds off its scent and send them in another direction. In an argument, this tactic is used in much the same way.
An arguer may introduce an irrelevant issue to deflect consideration of the matter at hand, to direct attention away from it. Sometimes known as the smokescreen fallacy, this tactic may result in complete abandonment of the original topic by focusing instead on the newly introduced, non-pertinent one. In effect, a new thread takes over and leaves the original one hanging.
One team member may be arguing for a redistribution of responsibilities when another slaps down a red herring: "Are we even sure we need to be doing all these things?" Others on the team chime in, and pretty soon the argument morphs into a discussion about whether the team should have those responsibilities rather than how to redistribute them.
The ad hominum (to the man) fallacy also redirects attention to the irrelevant. It attempts to discredit the opposition by calling names or insulting character, thereby avoiding discussion of issues and claims.
An arguer who insists that the results of a study are suspect because the scientist who conducted it received funding from an interested corporate or nonprofit source is making a personal attack upon the scientist. And having made such a charge, the arguer may well be able to turn discussion away from the study results to a discussion of the scientist, to the role of corporations and nonprofit entities in research, or even to a general mistrust of scientific investigations.
Latin for "you also," tu quoque is sometimes called an appeal to hypocrisy. It attempts to weaken the opponent's argument by claiming the opponent is a hypocrite who has committed the very actions she is arguing against. Thus in a city council meeting, one who argues for a tightening of the city employee code of ethics might be met with charges that she is a fine one to talk, that her own behavior has been unethical. And it might well have been—but her behavior is not relevant to the matter at hand. The issue is a revision of the code of ethics, and attention should focus on that, not on the character of one of its proponents.
The key, really, to such errors as these is relevance or its lack. As you construct arguments, participate in them, read or watch them, make relevance a touchstone. That's where the true issue is.