Full Idea
The proposition "Jupiter has four moons" can be converted into "the number of Jupiter's moons is four".
Gist of Idea
Convert "Jupiter has four moons" into "the number of Jupiter's moons is four"
Source
Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884], §57)
Book Reference
Frege,Gottlob: 'The Foundations of Arithmetic (Austin)', ed/tr. Austin,J.L. [Blackwell 1980], p.69
A Reaction
This seems to be the beginning of the modern exploration of the whole idea of logical form. It is one thing to find a logical forms which suits your current thesis (here, that numbers are not adjectival), but another to prove that it is the right form.
Related Idea
Idea 11031 'Jupiter has many moons' won't read as 'The number of Jupiter's moons equals the number many' [Rumfitt on Frege]