Argumentum ad Populum
Atheist call-in show hosts like to glibly dismiss some theistic callers as guilty of using the argumentum ad populum ; that's the claim that a proposition must be true because lots of people believe it to be true. This is considered an informal fallacy and a fallacy of relevance rather than a formal, or logical, fallacy. But is it really a fallacy? It depends, as we'll see. I'll say right at the top that no less a thinker than Aristotle held that our knowledge is and should be chock full of endoxa , which is Greek for reputable beliefs that almost all people hold without having personally confirmed them. Oops, by dropping Aristotle's name, did I just commit the fallacy of the argument from authority ( argumentum ab auctoritate ) ? We'll see. When I said above that "it depends," part of what I meant is that it depends on how we phrase the alleged fallacy. "That most everyone believes X is true proves that X is true" is clearly fallacious. But h...