Full Idea
The invitation to number the instances of some non-sortal concept is intelligible only if it is relativised to a sortal.
Gist of Idea
Instances of a non-sortal concept can only be counted relative to a sortal concept
Source
Crispin Wright (Frege's Concept of Numbers as Objects [1983], 1.i)
Book Reference
Wright,Crispin: 'Frege's Conception of Numbers' [Scots Philosophical Monographs 1983], p.3
A Reaction
I take this to be an essentially Fregean idea, as when we count the boots when we have decided whether they fall under the concept 'boot' or the concept 'pair'. I also take this to be the traditional question 'what units are you using'?
Related Idea
Idea 13865 'Sortal' concepts show kinds, use indefinite articles, and require grasping identities [Wright,C]