By David Lewis
Publisher: Cambridge University Press
Print Publication Year: 1999
Online Publication Date:February 2010
Chapter DOI: http://dx.doi.org/10.1017/CBO9780511625343.006
Subjects: Epistemology and metaphysics
Some properties of things are entirely intrinsic, or internal, to the things that have them: shape, charge, internal structure. Other properties are not entirely intrinsic: being a brother, being in debt, being within three miles of Carfax, thinking of Vienna. These properties are at least partly extrinsic, or relational Properties may be more or less extrinsic; being a brother has more of an admixture of intrinsic structure than being a sibling does, yet both are extrinsic.
A sentence or statement or proposition that ascribes intrinsic properties to something is entirely about that thing; whereas an ascription of extrinsic properties to something is not entirely about that thing, though it may well be about some larger whole which includes that thing as part. A thing has its intrinsic properties in virtue of the way that thing itself, and nothing else, is. Not so for extrinsic properties, though a thing may well have these in virtue of the way some larger whole is. The intrinsic properties of something depend only on that thing; whereas the extrinsic properties of something may depend, wholly or partly, on something else. If something has an intrinsic property, then so does any perfect duplicate of that thing; whereas duplicates situated in different surroundings will differ in their extrinsic properties.
The circles close. Two things are perfect duplicates iff they have the very same intrinsic properties. The way something is is given by the totality of its intrinsic properties.