Full Idea
Within each substance there is a perfect bond between the future and the past, which is what creates the identity of the individual.
Gist of Idea
Individuality is in the bond substance gives between past and future
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 2.01)
Book Reference
Leibniz,Gottfried: 'New Essays on Human Understanding', ed/tr. Remnant/Bennett [CUP 1996], p.114
A Reaction
I'm not quite sure if this means anything, but the idea that a bond across time is a necessity for intrinsic identity is interesting. The 'bond' would, I take it, have to be a causal one.