Full Idea
It does not seem that a relation adds anything real to that on which it is founded, but only makes for another real aspect belonging to the same thing. It is real since an aspect exists in re, not solely in the intellect, but it is not another thing.
Clarification
'In re' means in things themselves
Gist of Idea
Relations do not add anything to reality, though they are real aspects of the world
Source
Peter John Olivi (Summa quaestionum super Sententias [1290], II.54), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 12.4
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.236