Full Idea
Why can't we abstract a highly extrinsic aspect of something, say its surname, or its spatiotemporal location, or its role in a causal network, or its role in some body of theory? But these are unsuitable candidates for being genuine universals or tropes.
Gist of Idea
If we can abstract the extrinsic relations and features of objects, abstraction isn't universals or tropes
Source
David Lewis (On the Plurality of Worlds [1986], 1.7)
Book Reference
Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.85
A Reaction
(This is a criticism of the proposal in Idea 8905) Obviously we can abstract such things. In particular the role in a causal network is a function, which is a central example of an abstract idea. Russell keeps reminding us that relations are universals.
Related Idea
Idea 8905 If universals or tropes are parts of things, then abstraction picks out those parts [Lewis]