"As a Usenet discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one."
Godwin's Law is often cited in online discussions as a deterrent against the use of arguments in the reductio ad Hitlerum form.
The rule does not make any statement whether any particular reference or comparison to Hitler or the Nazis might be appropriate, but only asserts that one arising is increasingly probable. It is precisely because such a comparison or reference may sometimes be appropriate, Godwin has argued that overuse of Nazi and Hitler comparisons should be avoided, because it robs the valid comparisons of their impact. Although in one of its early forms Godwin's Law referred specifically to Usenet newsgroup discussions, the law is now applied to any threaded online discussion: electronic mailing lists, message boards, chat rooms, and more recently blog comment threads and wiki talk pages.
Godwin's Law applies especially to inappropriate, inordinate, or hyperbolic comparisons of other situations (or one's opponent) with Hitler or Nazis or their actions. It does not apply to discussions directly addressing genocide, propaganda, or other mainstays of the Nazi regime. Whether it applies to humorous use or references to oneself is open to interpretation, because although mentioning and trivializing Nazism in an online discussion, this would not be a fallacious attack against a debate opponent.
However, Godwin's Law itself can be abused, as a distraction or diversion, that fallaciously miscasts an opponent's argument as hyperbole, especially if the comparisons made by the argument are actually appropriate. A 2005 Reason magazine article argued that Godwin's Law is often misused to ridicule even valid comparisons.
Linking by implication the fallacy of reductio ad Hitlerum to online discussion length had been done prior to 1990 by a poster named Richard Sexton in 1989: "You can tell when a USENET discussion is getting old when one of the participants drags out Hitler and the Nazis." Godwin's Law does not, however, claim to articulate a fallacy; it is instead framed as a memetic tool to reduce the incidence of inappropriate hyperbolic comparisons. "Although deliberately framed as if it were a law of nature or of mathematics, its purpose has always been rhetorical and pedagogical: I wanted folks who glibly compared someone else to Hitler or to Nazis to think a bit harder about the Holocaust," Godwin has written It has not been established whether Sexton's quip had any influence on Godwin's law, though Sexton continues, citing an apparent joke by Godwin, to claim Godwin borrowed the idea from Sexton and named it.
The concept appears to have entered the public consciousness more broadly, as well. In 2005, the aphorism was the subject of a question in the British television quiz show University Challenge. By 2007, The Economist had declared that "a good rule in most discussions is that the first person to call the other a Nazi automatically loses the argument." And in October 2007, the "Last Page" columnist in The Smithsonian stated that when an adversary uses an inappropriate Hitler or Nazi comparison, "you have only to say 'Godwin's Law' and a trapdoor falls open, plunging your rival into a pool of hungry crocodiles."