Full Idea
In a class as many, the component terms, though they have some kind of unity, have less than is required for a whole.
Gist of Idea
A set has some sort of unity, but not enough to be a 'whole'
Source
Bertrand Russell (The Principles of Mathematics [1903], §070)
Book Reference
Russell,Bertrand: 'Principles of Mathematics' [Routledge 1992], p.69
A Reaction
This is interesting because (among many other things), sets are used to stand for numbers, but numbers are usually reqarded as wholes.