Full Idea
Classes or series of particulars, collected together on account of some property which makes it convenient to be able to speak of them as wholes, are what I call logical constructions or symbolic fictions.
Gist of Idea
Classes, grouped by a convenient property, are logical constructions
Source
Bertrand Russell (The Ultimate Constituents of Matter [1915], p.125)
Book Reference
Russell,Bertrand: 'Mysticism and Logic' [Unwin 1989], p.125
A Reaction
When does a construction become 'logical' instead of arbitrary? What is it about a property that makes it 'convenient'? At this point Russell seems to have built his ontology on classes, and the edifice was crumbling, thanks to Wittgenstein.