  Cooper argues that a natural history explanation needs to cite natural kinds if it is to be helpful. But in order to work the explanations do not need to cite the actual causal mechanisms responsible for the behaviour of the members of the kind in question. We know that Rex will devour the roast if we leave him in the kitchen with it, and we can safely make this prediction despite total ignorance of canine physiology. The history of psychiatry offers a number of instances in which pharmacology has led to the recognition of new kinds even in the absence of detailed causal knowledge. For example Cade’s (1949) discovery that lithium greatly inhibited the startle reflex and other forms of anxiety in guinea pigs was useful even without good information about their underlying cognitive neurobiology, since it led him to predict that whatever was going on might also apply in humans.