Full Idea
It would be strange if having learnt the lesson of multiple realisability that the same role may be filled by different states, we turned around and insisted that the converse - different roles filled by the same state - is impossible.
Gist of Idea
If different states can fulfil the same role, the converse must also be possible
Source
Frank Jackson (From Metaphysics to Ethics [1998], Ch.4 n3)
Book Reference
Jackson,Frank: 'From Metaphysics to Ethics' [OUP 2000], p.92
A Reaction
Good. The world is full of creatures who seem to enjoy the smell of decay etc. Some people (not me) like horror films. The separation of qualia and role leaves type-type physicalism as a possibility. Survival needs similar roles, not similar qualia.