Full Idea
Trope theory has the drawback that we need the primitive notion of duplicate tropes, whereas with universals we just say that it is one and the same universal through some charged particles.
Gist of Idea
Trope theory (unlike universals) needs a primitive notion of being duplicates
Source
David Lewis (On the Plurality of Worlds [1986], 1.5)
Book Reference
Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.65
A Reaction
The normal term for this primitive is 'perfect resemblance', though that seems to make close resemblance a bit complicated and puzzling. I'm not sure if I understand resemblance as a feature of the world, rather than of our minds.
Related Idea
Idea 15750 Tropes need a similarity primitive, so they cannot be used to explain similarity [Lewis]