Full Idea
If trope theorists say abstract singular terms name sets of tropes, what is the referent of 'is a unicorn'? The only candidate is the null set (with no members), but there is just one null set, so 'being a unicorn' and 'being a griffin' will be identical.
Gist of Idea
If abstract terms are sets of tropes, 'being a unicorn' and 'being a griffin' turn out identical
Source
Michael J. Loux (Metaphysics: contemporary introduction [1998], p.86)
Book Reference
Loux,Michael J.: 'Metaphysics: a contemporary introduction' [Routledge 2000], p.86
A Reaction
Not crucial, I would think, given that a unicorn is just a horse with a horn. Hume explains how we do that, combining ideas which arose from actual tropes.