Full Idea
By virtue of insensible variations, two individual things can never be perfectly alike.
Gist of Idea
No two things are totally identical
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], Pref)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.158
A Reaction
This sounds a bit like the 'discernibility of non-identicals', except that he says that the differences may not be 'sensible'. He has to be talking of physical things, since I presume that, say, the symmetry of two circles is perfectly identical.