Full Idea
Frege had a notorious difficulty over the concept 'horse', when he suggests that if we wish to assert something about a concept, we are obliged to proceed indirectly by speaking of an object that represents it.
Gist of Idea
An assertion about the concept 'horse' must indirectly speak of an object
Source
report of Gottlob Frege (Function and Concept [1891], Ch.2.II) by Bob Hale - Abstract Objects
Book Reference
Hale,Bob: 'Abstract Objects' [Blackwell 1987], p.35
A Reaction
This sounds like the thin end of a wedge. The great champion of objects is forced to accept them here as a façon de parler, when elsewhere they have ontological status.