This suggests that sometimes special causes and not their physical realizers might be responsible for physical effects. Suppose I want to hail a taxi, and that this desire is realized by some brain state, and that I then wave my arm. It seems that it will then be the desire that is proportional to the waving, not the brain state, in that I would still have waved my arm if my desire had been differently realized, though not if I hadn’t had the desire at all.