The main differences between a parliamentary and a presidential system of government lie in their structure and function. In a parliamentary system, the executive branch derives its legitimacy from the legislature, with the Prime Minister typically being a member of the parliamentary majority. This leads to a stronger connection between legislative and executive functions. Conversely, in a presidential system, the President is both the head of state and government, independently elected, which can lead to a more distinct separation of powers. These differences affect governance, stability, and the dynamics of political parties within each system.