&gt; <i>But then again, what can we really trust?</i><p>Textual evidence. The first demonstrable text wins, until an earlier is found. Sometimes it&#x27;s fuzzy, because quotes morph (they get pithier over time). But most of the time it&#x27;s clear enough, and the techniques for studying it are well understood.<p>Edit: The same is true in reverse, too: if a famous person really said X, it will be easy to find a precise textual source for X by googling. I don&#x27;t mean a website claiming they said it (those are legion), but the original text, e.g. from their collected works, or an original newspaper interview. Since they&#x27;re famous, that territory will have been trodden many times and there will be websites linking to it.  Therefore if you can&#x27;t find it, the famous person probably didn&#x27;t say it. “Absence of evidence is evidence of absence” (hey, I wonder who said that one?) really works in this case.