Full Idea
If we identify a psychological property with its causal role then we lose the obvious explanation of why the event has the causal role that it has.
Gist of Idea
If thoughts ARE causal, we can't explain how they cause things
Source
Gabriel M.A. Segal (A Slim Book about Narrow Content [2000], 4.1)
Book Reference
Segal,Gabriel M.A.: 'A Slim Book about Narrow Content' [MIT 2000], p.95
A Reaction
This pinpoints very nicely one of the biggest errors in modern philosophy. There are good naturalistic reasons to reduce everything to causal role, but there is a deeper layer. Essences!