Full Idea
You do not know how else [when one is added to one it becomes two] except by sharing in a particular reality, which does not have any other cause of becoming two except by sharing in Twoness, …as that which is one must share in Oneness.
Gist of Idea
One and one can only become two by sharing in Twoness
Source
Plato (Phaedo [c.374 BCE], 101c)
Book Reference
Plato: 'Complete Works', ed/tr. Cooper,John M. [Hackett 1997], p.87
A Reaction
Close readers of such passages have always been baffled by what sharing [partaking, metechein] could actually mean. How can two apples 'share' a pure eternal idea? The best approach is, I'm afraid, mental files.