Full Idea
The prevailing 'externalist' line on intentionality regards intentional states of mind as owing their content (what they are of, or about) to causal relations agents bear to the world.
Gist of Idea
The widespread externalist view says intentionality has content because of causal links of agent to world
Source
John Heil (Philosophy of Mind [1998], Ch.6)
Book Reference
Heil,John: 'Philosophy of Mind' [Routledge 1998], p.215
A Reaction
This goes back to Putnam's Twin Earth. 'Meanings aren't in the head'. I may defer to experts about what 'elm' means, but I may also be arrogantly wrong about what 'juniper' means.