Full Idea
A property is 'intrinsic' iff it never can differ between duplicates; iff whenever two things (actual or possible) are duplicates, either both of them have the property or both of them lack it.
Gist of Idea
A property is 'intrinsic' iff it can never differ between duplicates
Source
David Lewis (Defining 'Intrinsic' (with Rae Langton) [1998], IV)
Book Reference
Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.121
A Reaction
This leaves me wondering how one could arrive at a precise definition of 'duplicates'. Can it be done without mentioning that they have the same intrinsic properties?