Full Idea
Weak reduction of mind requires only that mental causes be identified with physical causes. A strong reduction requires also that the laws by which such causes operate follow by composition from non-special laws.
Clarification
The 'non-special' laws are the laws of physics
Gist of Idea
Weak reduction of mind is to physical causes; strong reduction is also to physical laws
Source
David Papineau (Thinking about Consciousness [2002], App 3 n8)
Book Reference
Papineau,David: 'Thinking about Consciousness' [OUP 2004], p.243
A Reaction
I'm cautious about laws, but I still vote for strong reduction. No new principles are needed to make a mind from a brain.