Full Idea
A plurality of things can neither be understood nor can exist unless one first understands the thing that is one, that to which the multitude necessarily reduces.
Gist of Idea
To exist and be understood, a multitude must first be reduced to a unity
Source
Gottfried Leibniz (Notes on Comments by Fardella [1690], Prop 3)
Book Reference
Leibniz,Gottfried: 'Philosophical Essays', ed/tr. Arlew,R /Garber,D [Hackett 1989], p.103
A Reaction
Notice that it is our need to understand which imposes the unity on the multitude. It is not just some random fiction, or a meaningless mechanical act of thought.