Full Idea
Identity should he considered a logical notion only because it is the tip of a second-order iceberg - a level 1 relation with a pure second-order definition.
Gist of Idea
Identity is a level one relation with a second-order definition
Source
Harold Hodes (Logicism and Ontological Commits. of Arithmetic [1984])
Book Reference
-: 'Journal of Philosophy' [-], p.124