Full Idea
The move from what can (or cannot) be known to exist to what does (or does not) exist has been dubbed the 'epistemic fallacy'.
Gist of Idea
The 'epistemic fallacy' is inferring what does exist from what can be known to exist
Source
Stathis Psillos (Causation and Explanation [2002], §1.6)
Book Reference
Psillos,Stathis: 'Causation and Explanation' [Acumen 2002], p.40
A Reaction
This should be a standard concept in all philosophical discussion. It is the commonest, simplest, and most profound blunder made by philosophers, and they do it all the time.