Full Idea
Both precise boundaries and universal applicability are built into the very notion of a Fregean concept from the outset, while isolation and non-arbitrary division are additional criteria imposed on concepts.
Gist of Idea
Fregean concepts have precise boundaries and universal applicability
Source
report of Gottlob Frege (Grundlagen der Arithmetik (Foundations) [1884]) by Kathrin Koslicki - Isolation and Non-arbitrary Division 2.1
Book Reference
-: 'Synthese' [-], p.407
A Reaction
The latter two criteria are for concepts which create counting units.