Power is often characterized as ‘zero-sum’. That is, power is something that A has over B, such that if A gains in power B correspondingly loses. However, the notion of power dependence suggests that power is also a relational concept, such that the power of A is dependent on B. The exercise of power is an exchange of resources and so A needs B—is dependent on B—in order to exercise power. An example is evident in Britain, where the power of the Prime Minister is dependent on the Cabinet recognizing his or her authority, and implementing his or her decisions.