Full Idea
My principle C seems unnecessary ...since it is one thing to see how many fs there are...but another to have a perfectly general method. ...One could answer whether this f-compliant is the same as that one, but there are too many ways to articulate it.
Gist of Idea
The sortal needed for identities may not always be sufficient to support counting
Source
David Wiggins (Sameness and Substance [1980], 2.8)
Book Reference
Wiggins,David: 'Sameness and Substance' [Blackwell 1980], p.73
A Reaction
His famous example is trying to count the Pope's crown, which is made of crowns. A clearer example might be a rectangular figure divided up into various overlapping rectangles. Individuation is easy, but counting is contextual.