Full Idea
The word 'Julius Caesar is prime' may well involve some kind of category error, but the still compose a grammatical sentence. The words 'There are exactly Julius Caesar moons of Mars', by contrast, are gibberish.
Gist of Idea
The words 'There are exactly Julius Caesar moons of Mars' are gibberish
Source
comment on Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884]) by Ian Rumfitt - Concepts and Counting p.48
Book Reference
-: 'Aristotelian Society' [], p.48