Full Idea
Teleological functions help explain why a trait has come to exist; causal-role functions tell what a trait does or is apt to do.
Clarification
'Teleology' concerns purposes
Gist of Idea
Teleological functions explain why a trait exists; causal-role functions say what it does
Source
Thomas W. Polger (Natural Minds [2004], §5.4)
Book Reference
Polger,Thomas W.: 'Natural Minds' [MIT 2004], p.174
A Reaction
The teleological view has the merit of nesting nicely with the theory of evolution, and with Aristotelian virtue ethics (which I like). Causal-role functionalism focuses better on what is actually happening inside the head.