Constitutional legitimacy is a question which asks us what makes a constitution legitimate. Why should we still obey laws today that were written so long ago, when the world was a different place? The most popular theory is consent of the governed. This theory states that the people consent to the Constitution, like any other contract, and are later bound by its terms. But some argue since the Constitution binds all citizens, such consent would need to be unanimous, which is impractical in such a large country. Randy Barnett has proposed what he calls the "necessary and proper" theory of constitutional legitimacy in his book, Restoring the Lost Constitution.