 A third major area where the concept of intrinsicality has been put to work is in stating various supervenience theses. Frank Jackson (1998) defines physicalism in terms of duplication and physical duplication, which are in turn defined in terms of intrinsic properties. Similarly, Jaegwon Kim (1982) defines a mind/body supervenience thesis in terms of intrinsic properties. As Theodore Sider (1993) notes, the simplest way to define the individualist theory of mental content that Tyler Burge (1979) attacks is as the claim that the content of a thinker’s propositional attitudes supervenes on the intrinsic properties of the thinker. And many internalist theories in epistemology are based around the intuition that whether a thinker is justified in believing some proposition supervenes on the intrinsic properties of the thinker.