Full Idea
Isn't it logically possible that the universe should have contained nothing but two exactly similar spheres? ...So two things would have all their properties in common, and this would refute the Principle of the Identity of Indiscernibles.
Gist of Idea
If the universe just held two indiscernibles spheres, that refutes the Identity of Indiscernibles
Source
Max Black (The Identity of Indiscernibles [1952], p.67)
Book Reference
'Metaphysics - An Anthology', ed/tr. Sosa,E. /Kim,J. [Blackwell 1999], p.67
A Reaction
[Black is the originator of this famous example] It also appears to be naturally possible. An observer at an instant of viewing will discern a relational difference relative to themselves. Most people take Black's objection to be decisive.
Related Ideas
Idea 13788 If we made a perfect duplicate of Cratylus, there would be two Cratyluses [Plato]
Idea 13178 Things in different locations are different because they 'express' those locations [Leibniz]