Full Idea
A problem which Frege called to our attention is: how can identities be informative?
Gist of Idea
Frege was asking how identities could be informative
Source
report of Gottlob Frege (On Sense and Reference [1892]) by John Perry - Knowledge, Possibility and Consciousness §5.2
Book Reference
Perry,John: 'Knowledge, Possibility and Consciousness' [MIT 2001], p.100
A Reaction
E.g. (in Russell's example) how is "Scott is the author of 'Waverley'" more informative than "Scott is Scott"? A simple answer might just be that informative identities also tell you of a thing's properties. "The red ball is the heavy ball".