Full Idea
Each individual is distinct from each other individual, so the bundle account of objects requires each bundle to be different from every other bundle. So the Identity of Indiscernibles must be a necessary truth, which, unfortunately, it is not.
Gist of Idea
Bundles must be unique, so the Identity of Indiscernibles is a necessity - which it isn't!
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
Clearly the Identity of Indiscernibles is not a necessary truth (consider just two identical spheres). Location and time must enter into it. Could we not add a further individuation requirement to the necessary existence of a bundle? (Quinton)