Full Idea
It is impossible for us to know individuals or to find any way of precisely determining the individuality of any thing except by keeping hold of the thing itself.
Gist of Idea
The only way we can determine individuals is by keeping hold of them
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 3.03)
Book Reference
Leibniz,Gottfried: 'New Essays on Human Understanding', ed/tr. Remnant/Bennett [CUP 1996], p.289
A Reaction
'The tallest woman in London' seems to determine someone perfectly well, though only by cross-referencing universal concepts like 'tall'.