Full Idea
Anything that genuinely exists is supported by the true and rigorous argument that neither of two distinct entities can ever occur in the other, because that would simultaneously make them one and two.
Gist of Idea
Two existing entities can never strictly coincide
Source
Plato (Timaeus [c.362 BCE], 52c)
Book Reference
Plato: 'Timaeus and Critias', ed/tr. Waterfield,Robin [OUP 2008], p.45
A Reaction
A pair of boots is one and two, but maybe our seeing them or naming them that way cannot be precisely simultaneous. If a salt molecule is two things, does it therefore not exist? On the whole I agree with Plato!