Circulation theory?
I suggest that you could also call `circulation theory' a simple piece of legislation by Mr Newton.
The flowing air lifts up the wing, and the wing pushes down the flowing air.
Behind the aircraft, air is now descending, to a good first order, to the tune of `lift = rate of change of vertical momentum in the airflow', while behind the aircraft the air is also made to follow along, to a first order, to the tune of `drag = rate of change of horizontal momentum in the airflow'.