In mobility, many people move up the social class ladder, and many move down, with the social class system showing little change.

I believe the answer is: Exchange mobility
In exchange mobility, the society is divided into several classes, but the member of each classes is expected to remain static.
So, if a members in this society intended to move up in social ladder, other member has to move down in social ladder and be replaced.

Ifound this on google “separation of powers. a fundamental principle of the united states government, whereby powers and responsibilities are divided among the legislative branch, executive branch, and judicial branch.” i hope this you for what your looking for