Full Idea
The formal properties of identity are the reflexivity of identity, and Leibniz's Law (if x is the same as y, then whatever is true of one is true of the other).
Gist of Idea
The formal properties of identity are reflexivity and Leibniz's Law
Source
David Wiggins (Sameness and Substance Renewed [2001], Pr.2)
Book Reference
Wiggins,David: 'Sameness and Substance Renewed' [CUP 2001], p.4
A Reaction
Presumably transitivity will also apply, and, indeed, symmetry. He seems to mean something like the 'axiomatic formal properties'.
Related Idea
Idea 16017 Identity is usually defined as the equivalence relation satisfying Leibniz's Law [Noonan]