Full Idea
Parthood (for the three-dimensionalist) must be a three-place relation between pairs of objects and times, not the timeless two-place relation at work in the original Calculus of Individuals.
Gist of Idea
For three-dimensionalist parthood must be a three-place relation, including times
Source
Kathrin Koslicki (The Structure of Objects [2008], 2.2)
Book Reference
Koslicki,Kathrin: 'The Structure of Objects' [OUP 2008], p.25