Full Idea
It is natural to suppose one only uses a definite description when one believes it describes only one thing, but exceptions are 'there is no such thing as the greatest prime number', or saying something false where the reference doesn't occur.
Gist of Idea
Definite descriptions don't always pick out one thing, as in denials of existence, or errors
Source
David Bostock (Intermediate Logic [1997], 8.3)
Book Reference
Bostock,David: 'Intermediate Logic' [OUP 1997], p.342