Full Idea
Logical truths should be true no matter what exists, so true even if nothing exists. The classical predicate calculus, however, makes it logically true that something exists.
Gist of Idea
Logical truths are true no matter what exists - but predicate calculus insists that something exists
Source
Oliver,A/Smiley,T (What are Sets and What are they For? [2006], 5.1)
Book Reference
'Metaphysics (Philosophical Perspectives 20)', ed/tr. Hawthorne,John [Blackwell 2006], p.145