Full Idea
We can't define the mental as intentional because pains aren't about anything, and we can't define it as phenomenal because beliefs don't feel like anything.
Clarification
'Intentional' events are about things; 'phenomenal' events feel like something
Gist of Idea
Pain lacks intentionality; beliefs lack qualia
Source
Richard Rorty (Philosophy and the Mirror of Nature [1980], 1.2)
Book Reference
Rorty,Richard: 'Philosophy and the Mirror of Nature' [Blackwell 1980], p.22
A Reaction
Nice, but simplistic? There is usually an intentional object for a pain, and the concepts which we use to build beliefs contain the residue of remembered qualia. It seems unlikely that any mind could have one without the other (even a computer).