by Eliezer Yudkowsky May 25 2016

To call something a fallacy is to assert that you think people shouldn't think like that.

A "fallacy" is a mode of thought that is asserted (by calling it a "fallacy") to lead us easily into error, or to not usefully contribute to the project of distinguishing truth from falsehood. For example, Argumentum Ad Hitlerum is a 'fallacy' because while Hitler did a number of bad things, he also ate vegetables, so "Hitler did X" is not a reliable means of arguing that nobody should do X.