Full Idea
Space is a relationship: an order, not only among existents, but also among possibles as though they existed.
Gist of Idea
Space is an order among actual and possible things
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], 2.13)
Book Reference
Leibniz,Gottfried: 'New Essays on Human Understanding', ed/tr. Remnant/Bennett [CUP 1996], p.149
A Reaction
The modal end to this idea is a bit puzzling. Would there be any space if there were only possibles, and nothing yet existed, as in God's mind the instant before he got to work?