Vacuousness and Grice's System Q

From M. R.'s online 'nonexistent objects', Stanford Encyclopedia:

"The problem of fictional discourse is closely connected to two logical principles. The first one is well known as “the principle of existential generalization”:
Existential Generalization (EG):
Fb → ∃x(Fx), i.e.,
If b is F, then there is something that is F.[4]
The second principle is less prominent, rather seldom explicitly stated, but often tacitly assumed. We call it “the predication principle”:
Predication Principle (PP):
Fb → ∃x(x = b).
(PP) may be read in two ways:
(PPa) If b is F, then there is something that is identical with b.
(PPb) If b is F, then b exists.
Both principles are prima facie extremely plausible."