Full Idea
It is impossible for us to have knowledge of individuals and to find the means of determining exactly the individuality of everything.
Gist of Idea
We can't know individuals, or determine their exact individuality
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 3.3)
Book Reference
Leibniz,Gottfried: 'New Essays on Human Understanding', ed/tr. Remnant/Bennett [CUP 1996], p.289
A Reaction
Aristotle was clearly also tempted by this doubt (since universals are involved), though individuals are what he wanted to understand. I think they are wrong. Leibniz gives the bizarre reason that we can't know individuals as they each contain infinity.