 Historically, however, the reason for the current dominance of desire theories lies in the emergence of welfare economics. Pleasure and pain are inside people’s heads, and also hard to measure—especially when we have to start weighing different people’s experiences against one another. So economists began to see people’s well-being as consisting in the satisfaction of preferences or desires, the content of which could be revealed by the choices of their possessors. This made possible the ranking of preferences, the development of ‘utility functions’ for individuals, and methods for assessing the value of preference-satisfaction (using, for example, money as a standard).