Full Idea
Enduring objects should be taken as fundamental in an ontology, and for all such objects indiscernibility is both a necessary and sufficient condition for identity.
Clarification
'Indiscernibility' is not being able to tell them apart
Gist of Idea
Indiscernibility is a necessary and sufficient condition for identity
Source
Baruch Brody (Identity and Essence [1980], 3)
Book Reference
Brody,Baruch: 'Identity and Essence' [Princeton 1980], p.43
A Reaction
Brody offers a substantial defence, but I don't find it plausible. Apart from Black's well known twin spheres example (Idea 10195), discernibility is relative to the powers of the observer. Two similar people in the mist aren't thereby identical.
Related Idea
Idea 10195 If the universe just held two indiscernibles spheres, that refutes the Identity of Indiscernibles [Black]