It is merely a theory that explains how free enterprise works. Banks for example, a very important part of the economy, are left out. Some socities do not accept the circular flow model theory. These socities, therefore, choose another economic system other than capitalism. Socialists and communists see the role of the government in a different light than capitalists do.
The United States Constitution states that the Vice President of the United States is the President of the Senate, despite not being a senator, and that the Senate must choose a president pro tempore.
The head of the House of Saud is the King of Saudi Arabia who serves as Head of State and monarch of the Kingdom of Saudi Arabia. The King holds almost absolute political power. The King appoints ministers to his cabinet who supervise their respective ministries in his name.