Full Idea
Substantial unity requires a complete, indivisible and naturally indestructible entity, since its concept embraces everything that is to happen to it, which cannot be found in shape or motion.
Gist of Idea
Unity needs an indestructible substance, to contain everything which will happen to it
Source
Gottfried Leibniz (Letters to Antoine Arnauld [1686], 1686.11.28/12.8)
Book Reference
Leibniz,Gottfried: 'The Leibniz-Arnauld Correspondence', ed/tr. Mason,HT/Parkinson,GHR [Manchester UP 1967], p.94
A Reaction
Hence if a tile is due to be broken in half (Arnauld's example), it cannot have had unity in the first place. To what do we refer when we say 'the tile was broken'?