Full Idea
Rather than directly constructing properties as sets of objects and proving neat facts about properties by proxy, we can assert biconditionals, such as that an object has a property if and only if it is in a certain set.
Gist of Idea
Construct properties as sets of objects, or say an object must be in the set to have the property
Source
Bernard Linsky (Russell's Metaphysical Logic [1999], 7.6)
Book Reference
Linsky,Bernard: 'Russell's Metaphysical Logic' [CSLI 1999], p.137
A Reaction
Linsky is describing Russell's method of logical construction. I'm not clear what is gained by this move, but at least it is a variant of the usual irritating expression of properties as sets of objects.