Full Idea
Mind-to-behaviour connections are always defeasible - by the occurrence of a further mental state.
Clarification
A theory is 'defeasible' if there could be evidence which counted heavily against it.
Gist of Idea
Behaviour depends on lots of mental states together
Source
Jaegwon Kim (Philosophy of Mind [1996], p. 35)
Book Reference
Kim,Jaegwon: 'Philosophy of Mind' [Westview 1998], p.35
A Reaction
But then an object's falling under gravity is always defeasible, by someone catching it first. This popular idea is meant to show that there could, as Davidson puts it, 'no psycho-physical laws', but I suspect the laws are just complex, like weather laws.