A presidential system is a system of government where a head of government is also head of state and leads an executive branch that is separate from the legislative branch. The United States, for instance, has a presidential system. The executive is elected and often titled "president" and is not responsible to the legislature and cannot, in normal circumstances, dismiss it. The legislature may have the right, in extreme cases, to dismiss the executive, often through impeachment. However, such dismissals are seen as so rare as not to contradict a central tenet of presidentialism, that in normal circumstances using normal means the legislature cannot dismiss the executive.