Full Idea
An objection to the 'covariance' theory of content is that what you believe is influenced, often crucially, by what else you believe.
Gist of Idea
Content depends on other content as well as the facts
Source
Jaegwon Kim (Philosophy of Mind [1996], p.193)
Book Reference
Kim,Jaegwon: 'Philosophy of Mind' [Westview 1998], p.193
A Reaction
I can't think of a reply to this, if the covariance theory is suggesting that content just IS covariance of mental states with the environment. Externalism says that mind extends into the world.