Full Idea
If a bit of matter has a qualitatively indistinguishable object located at a later time, with a path of spacetime connecting them, how could we determine they are identical? Neither identity nor diversity follows from qualitative indiscernibility.
Gist of Idea
If two objects are indiscernible across spacetime, how could we decide whether or not they are the same?
Source
Michael Jubien (Possibility [2009], 1.3)
Book Reference
Jubien,Michael: 'Possibility' [OUP 2009], p.13
A Reaction
All these principles expounded by Leibniz were assumed to be timeless, but for identity over time the whole notion of things retaining identity despite changing has to be rethought. Essentialism to the rescue.