Full Idea
A set is 'a number of things', not a 'collection'. Nothing literally 'collects' the members of a set, such as the set of planets of the sun, unless it be a Fregean 'concept' under which they fall.
Gist of Idea
A set is a 'number of things', not a 'collection', because nothing actually collects the members
Source
E.J. Lowe (The Possibility of Metaphysics [1998], 10.6)
Book Reference
Lowe,E.J.: 'The Possibility of Metaphysics' [OUP 2001], p.221
A Reaction
I'm tempted to say that the sun has collected a set of planets (they're the ones that rotate around it). Why can't we have natural sets, which have been collected by nature? A question of the intension, as well as the extension....