Statement of Godwin's Law
As an online discussion grows longer, the probability of a comparison involving Nazis or Hitler approaches one.
Usage in internet discussions
There is a tradition in Internet discussion forums that once such a comparison is made, the thread in question is finished and whoever mentioned the Nazis has automatically "lost" whatever debate was in progress.
Godwin's Law thus serves to impose an upper bound on thread length in general.
It is considered poor form to raise arbitrarily such a comparison with the motive of ending the thread. There is a widely recognized codicil that any such ulterior-motive invocation of Godwin's Law will be unsuccessful.
Godwin's Law does not apply to discussions directly addressing genocide, propaganda or other mainstays of the Nazi regime. Instead, it applies to inappropriate, inordinate, or hyperbolic comparisons of other situations to Hitler or Nazis.