I think that having the belief that there's a rabbit in the yard is a matter of having some suitable combination of dispositions to action, dispositions to experience qualia, relations to the external world ect. (roughly: those that would make an omniscient Davidsonain charitable interpreter attribute you the belief that there's a rabbit in the yard)
But (I think) exactly which dispositions etc. are required is quite complicated, and in some respects arbitrary (e.g. verbal behavior that would equally well track the facts about rabbits and undetached rabbit parts counts as referring to rabbits).
Does this view that 'believing that there's a rabbit in the yard' may not pick out any supremely natural combination of mental states, prevent me from saying that beliefs can cause things?
The facts about what physical combinations of stuff count as a baseball are equally complicated and arbitrary. But no one would deny that baseballs can figure in causal explanations e.g. the window broke because someone threw a baseball at it.
Just as the somewhat arbitrary fact that a regulation baseball has to have a diameter of between two and seven-eighths inches and three inches doesn't prevent talk of baseballs from figuring in causal claims, the somewhat arbitrary fact that it's easier to count as referring to/thinking about rabbits rather than undetached rabbit parts doesn't prevent talk of beliefs from figuring in causal claims.