A do not know to not-being - A nescire ad non esse
A nescire ad non esse ( Latin for “from not knowing to not being”) describes a rhetorical figure that is one of the ad-populum arguments. An assertion that something is not the case is justified by the fact that the facts are not known (e.g. "It cannot be like this, (because) I have never heard it like this"). But it is not a logically valid argument; if so treated, it produces a fallacy . 
- Entry in Herder's Conversations Lexicon. Freiburg im Breisgau 1854, Volume 1, p. 185. online at zeno.org.