The view that a legislative chamber should be properly composed of two houses. In the majority of states, the second or upper house has a more restricted role, for example limited to checking or delaying legislation introduced in the lower house, but an important exception is the United States where both the Senate and the House of Representatives play an important role in the legislative process. In such a system where the two houses have broadly equivalent power, it is necessary to provide a mechanism to resolve differences between them, such as joint committees. In federal systems, the upper house often represents the units of the federation, which may be given an equal number of seats regardless of their size, as in the United States. In Germany, the consent of the upper house, the Bundesrat, which is not directly elected, is necessary in those areas which directly affect the competence of the federal units or Länder. Purely appointed bodies such as the Canadian Senate, whose members are appointed by the federal prime minister, may lack legitimacy, although it has provided ministers from provinces where the governing party is weak. Second chambers differ considerably in their methods of appointment or election, legitimacy, powers, and effective political role, making it difficult to advance a coherent philosophy of bicameralism. In the UK, this incoherence has been evident in the repeated attempts to reform the House of Lords, with conflicting claims about the nature of the relationship with the House of Commons and the need for representativeness, independence, and accountability.