Full Idea
Frege's theory of properties (which he calls 'concepts') yields too few properties, by identifying coextensive properties, and also too many, by letting every predicate express a property.
Clarification
'Coextensive' properties apply to the same objects; predicates are linguistic expressions of properties
Gist of Idea
Frege allows either too few properties (as extensions) or too many (as predicates)
Source
comment on Gottlob Frege (Function and Concept [1891]) by DH Mellor / A Oliver - Introduction to 'Properties' §2
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.4
A Reaction
Seems right; one extension may have two properties (have heart/kidneys), two predicates might express the same property. 'Cutting nature at the joints' covers properties as well as objects.