On some aircraft, it might not necessarily have anything to do with hydraulics. The DC9 / MD80 the control surfaces are moved by way of a servo tab (like a trim tab). The only exception is that they have a hydraulic supply to the elevator for down only (to recover from a super stall) and the rudder (for full rudder control in the event of an engine failure on take off) - ( the rudder supply is taken from the rear stair accumulator, so if the rear stairs don't work you can't go!). It is quite common to see an MD80 taxiing out with one elevator up and one down, blown that way by the wind. The control wheel only operates the servo tabs and not the main control suface. For this they need airflow. The ailerons are balanced together and sprung loaded centre. If you turn the wheel without airflow over the wings the ailerons don't move, only the tabs. Likewise the elevator except that if you push the control column forward the hydraulic supply (if on) will push both elevators down.
Incidently this system of control was used as a back-up system for the Spuce Goose, by Howard Hughes.
Bob