Full Idea
Perhaps there is no objection to quantifying into modal contexts as long as the values of any variables thus quantified are limited to intensional objects, but they also lead to disturbing examples.
Clarification
'Intensional' objects are in thought rather than in reality
Gist of Idea
Maybe we can quantify modally if the objects are intensional, but it seems unlikely
Source
Willard Quine (Reference and Modality [1953], §3)
Book Reference
Quine,Willard: 'From a Logical Point of View' [Harper and Row 1963], p.152
A Reaction
[Quine goes on to give his examples] I take it that possibilities are features of actual reality, not merely objects of thought. The problem is that they are harder to know than actual objects.