Full Idea
In standard logic we can't straightforwardly say that n exists. We have to resort to using a formula like '∃x(x=n)', but we can't deny n's existence by negating that formula, because standard first-order logic disallows empty names.
Gist of Idea
In first-order we can't just assert existence, and it is very hard to deny something's existence
Source
Kent Bach (What Does It Take to Refer? [2006], 22.2 L1)
Book Reference
'Oxford Handbook of Philosophy of Language', ed/tr. Lepore,E/Smith,B [OUP 2008], p.538