  To desire is to be in a particular state of mind. It is a state of mind familiar to everyone who has ever wanted to drink water or desired to know what has happened to an old friend, but its familiarity does not make it easy to give a theory of desire. Controversy immediately breaks out when asking whether wanting water and desiring knowledge are, at bottom, the same state of mind as others that seem somewhat similar: wishing never to have been born, preferring mangoes to peaches, craving gin, having world conquest as one's goal, having a purpose in sneaking out to the shed, or being inclined to provoke just for the sake of provocation. These varied states of mind have all been grouped together under the heading of ‘pro attitudes’, but whether the pro attitudes are fundamentally one mental state or many is disputed.