Full Idea
When Thomae says "abstract from the peculiarities of the individual members of a set of items", or "disregard those characteristics which serve to distinguish them", we get a general concept under which they fall. The things keep their characteristics.
Gist of Idea
Thomae's idea of abstract from peculiarities gives a general concept, and leaves the peculiarities
Source
comment on C.J. Thomae (works [1869], §34) by Gottlob Frege - Grundlagen der Arithmetik (Foundations) §34
Book Reference
Frege,Gottlob: 'The Foundations of Arithmetic (Austin)', ed/tr. Austin,J.L. [Blackwell 1980], p.45
A Reaction
Interesting. You don't have to leave out their distinctive fur in order to count cats. But you have to focus on some aspect of them, because they aren't 'three meats'.