Full Idea
There is 'partial identity' where one entity contains another with something to spare, or else where entities overlap each other. ...Extensive quantities, such as length and mass, are the particularly plausible cases.
Gist of Idea
When entities contain entities, or overlap with them, there is 'partial' identity
Source
David M. Armstrong (Truth and Truthmakers [2004], 08.5)
Book Reference
Armstrong,D.M.: 'Truth and Truthmakers' [CUP 2004], p.103
A Reaction
This looks like a very useful concept which deserves wider use. It will help discussions of rivers, statues, intersecting roads etc.