Full Idea
Plato considers a 'container' model for wholes (which are disjoint from their parts) [Parm 144e3-], and a 'nihilist' model, in which only wholes are mereological atoms, and a 'bare pluralities' view, in which wholes are not really one at all.
Gist of Idea
Plato says wholes are either containers, or they're atomic, or they don't exist
Source
report of Plato (works [c.375 BCE]) by Kathrin Koslicki - The Structure of Objects 5.2
Book Reference
Koslicki,Kathrin: 'The Structure of Objects' [OUP 2008], p.96
A Reaction
[She cites Verity Harte for this analysis of Plato] The fourth, and best, seems to be that wholes are parts which fall under some unifying force or structure or principle.