Full Idea
The null set serves two useful purposes. It is a denotation of last resort for class abstracts that denote no nonempty class. And it is an individual of last resort: we can count on its existence, and fearlessly build the hierarchy of sets from it.
Gist of Idea
The null set plays the role of last resort, for class abstracts and for existence
Source
David Lewis (Mathematics is Megethology [1993], p.09)
Book Reference
-: 'Philosophia Mathematica' [-], p.9
A Reaction
This passage assuages my major reservation about the existence of the null set, but at the expense of confirming that it must be taken as an entirely fictional entity.