Full Idea
Quantity or extension adds absolutely nothing really distinct to the quantified matter or to the extended and quantified form, except perhaps the union and location and position of those parts.
Gist of Idea
Quantity just adds union and location to the extension of parts
Source
Peter John Olivi (Summa quaestionum super Sententias [1290], II:58,II:440), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 14.1
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.281
A Reaction
Other views seem to say that the Quantity provides the extension, but he seems to take that as given.