Full Idea
The idea of supervenience is when there could be no difference of one sort without difference of another sort. ..Clearly this 'could' indicates modality, and without modality we have nothing of interest.
Gist of Idea
Supervenience concerns whether things could differ, so it is a modal notion
Source
David Lewis (On the Plurality of Worlds [1986], 1.2)
Book Reference
Lewis,David: 'On the Plurality of Worlds' [Blackwell 2001], p.15
A Reaction
This might explain why philosophers are going to be more at home with the concept than neuroscientists would be.