Full Idea
Logical consequence guarantees preservation of truth. The Converse Barcan, a theorem of Simple Quantified Modal Logic, says that an obvious truth implies an obvious falsehood. So SQML gets logical consequence wrong. So SQML is mistaken.
Gist of Idea
Simple Quantified Modal Logc doesn't work, because the Converse Barcan is a theorem
Source
Trenton Merricks (Propositions [2015], 2.V)
Book Reference
Merricks,Trenton: 'Propositions' [OUP 2015], p.65
A Reaction
I admire this. The Converse Barcan certainly strikes me as wrong (Idea 19208). Merricks grasps this nettle. Williamson grasps the other nettle. Most people duck the issue, I suspect. Merricks says later that domains are the problem.
Related Idea
Idea 19208 The Converse Barcan implies 'everything exists necessarily' is a consequence of 'necessarily, everything exists' [Merricks]