Full Idea
The Identity of Indiscernibles is not a necessary truth. It fails in possible worlds where there are two identical spheres in a non-absolute space, or worlds without beginning or end where events are exactly cyclically repeated.
Clarification
The principle (associated with Leibniz) claims that if two things can't be distinguished they are the same
Gist of Idea
Two pure spheres in non-absolute space are identical but indiscernible
Source
Keith Campbell (The Metaphysic of Abstract Particulars [1981], §5)
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.132
A Reaction
The principle was always very suspect, and these seem nice counterexamples. As so often, epistemology and ontology had become muddled.