Full Idea
The instrument of generality in mathematics is the variable.
Gist of Idea
Mathematics generalises by using variables
Source
J. Alberto Coffa (The Semantic Tradition from Kant to Carnap [1991], 4 'The conc')
Book Reference
Coffa,J.Alberto: 'The Semantic Tradition from Kant to Carnap' [CUP 1993], p.69
A Reaction
I like the idea that there are variables in ordinary speech, pronouns being the most obvious example. 'Cats' is a variable involving quantification over a domain of lovable fluffy mammals.