Columnist: If you received an unsigned letter, you would likely have some doubts about the truth of its contents. But news stories often include statements from anonymous sources, and these are usually quoted with the utmost respect. It makes sense to be skeptical of these sources, for, as in the case of the writer of an unsigned letter, their anonymity makes it possible for them to plant inaccurate or slanted statements without ever having to answer for them. The columnist's argument proceeds by ['calling into question the motives of those presenting certain information, and concluding for this reason that the information is likely to be false', 'calling into question a certain type of evidence by drawing an analogy between that evidence and other evidence that the argument shows is usually false', 'inferring that an attitude would be justified in all situations of a given type on the grounds that this attitude is justified in a hypothetical situation of that type', 'pointing out that a certain attitude would presumably be adopted in one situation, in order to support the claim that a similar attitude would be justified in an analogous situation']