Full Idea
Properties may be more or less intrinsic; being a brother has more of an admixture of intrinsic structure than being a sibling does, yet both are extrinsic.
Gist of Idea
Extrinsic properties come in degrees, with 'brother' less extrinsic than 'sibling'
Source
David Lewis (Extrinsic Properties [1983], I)
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.111
A Reaction
I suppose the point is that a brother is intrinsically male - but then a sibling is intrinsically human. A totally extrinsic relation would be one between entities which shared virtually no categories of existence.