Full Idea
All the things we refer to as pluralities (e.g. beautiful things) we also count as belonging to a single class by virtue of the fact that they have a single particular character.
Gist of Idea
The plurality of beautiful things must belong to a single class, because they have a single particular character
Source
Plato (The Republic [c.371 BCE], 507b)
Book Reference
Plato: 'Republic', ed/tr. Waterfield,Robin [OUP 1993], p.233