Actually, I just used the phrase "rule of thumb" in a conversation on a completely different matter less than an hour earlier. I was talking a friend (from Harrisburg, PA) who was telling me a story about someone who was trying to tell her that so-called Legal Sea Foods, as a matter of regular corporate practice, sells fish that are actually two years old as being fresh. When she told the person that they were either mistaken or lying, the person responded that they weren't mistaken and weren't lying because, on the latter possibility, "Why would I lie?" My own rule of thumb regarding Why-Would-I-Lie: Whenever someone says "Why would I lie?," they are probably lying. People lie for all kinds of obscure, unfathomable, or completely irrational reasons, and some may even lie for no reason at all. Just because I can't rationalize another person's lying doesn't mean that I need to believe what they are saying. (A corollary to this being that just because you can rationalize another person's lying doesn't mean that they aren't telling the truth.)*
* Aside: People occasionally note to me that I seem to regularly use constructions like "Whenever someone..., they...." instead of "Whenever someone..., he...." or "Whenever someone..., he or she....", etc.. While readers might regard my usage as erroneous, it is actually the recommended construction in the Official JFW Manual of Style, as the editors of this weblog believe (a) that the pseudo-singular "they" will become increasingly frequently used in the future and (b) that the whole aspiration of this weblog is to be part of the future now.
Update, midnight: A reader from Mutton, NE notes that some people think that you should base your entire set of existential and spiritual beliefs on the Why-Would-They-Lie argument form. As evidence, he cuts-and-pastes the following text to me from some online-proselytization-resource:
Bible Truth - The Passion of the Ancient Writers
When it comes to Bible truth, many critics argue that the early Church deliberately corrupted the Bible's text for its own agenda. As for this argument, ask yourself one question: would a group of men who were willing to suffer terrible persecution and die horrible deaths in defense of the Scriptures be guilty of corrupting those very same Scriptures? That's lunacy! If they corrupted the Scriptures, or knowingly allowed them to be corrupted, that would mean they knowingly suffered and died for a lie! No one suffers and dies for a lie!
[T]he September 11th suicide hijackers may have sincerely believed in what they died for, but they didn't knowingly die for a lie; they died for a lie in ignorance... In contrast, the New Testament's martyrs either saw what they claimed to see or they didn't; plain and simple. Either they interacted with the resurrected Christ or they didn't. They certainly knew whether or not their testimony was true! Nevertheless, these men clung to their testimonies, even to their brutal deaths at the hands of their persecutors, and despite being given every chance to recant, knowing full well whether their testimony was true of false. Why would so many men knowingly die for a lie? They had nothing to gain for lying and obviously everything to lose.