Full Idea
The first demand of logic is of a sharp boundary.
Gist of Idea
The first demand of logic is of a sharp boundary
Source
Gottlob Frege (Grundgesetze der Arithmetik 2 (Basic Laws) [1903], §160), quoted by Michael Dummett - Frege philosophy of mathematics Ch.22
Book Reference
Dummett,Michael: 'Frege: philosophy of mathematics' [Duckworth 1991], p.277
A Reaction
Nothing I have read about vagueness has made me doubt Frege's view of this, although precisification might allow you to do logic with vague concepts without having to finally settle where the actual boundaries are.