Full Idea
There must be more in the concept of a thing which exists than in that of one which does not exist.
Gist of Idea
The concept of an existing thing must contain more than the concept of a non-existing thing
Source
Gottfried Leibniz (On the Principles of Indiscernibles [1696], p.134)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.134