u/Papelera-DeReciclaje

I still don't quite grasp when I should identify it, when it isn't a fallacy or whether it is actually very common in public discourse.

Are these examples of ad ignorantiam? "I don't understand chemistry, nor can I demonstrate it; therefore, the periodic table doesn't exist" or "I’ve never seen your sister, so she must not exist".

I’ve been reading about formal and informal fallacies for at least a year now, , but I'm still confused.