In the early 80s at several large universities I knew of, it wasn't uncommon for attendance at lectures to be effectively optional. The student was expected to

In the early 80s at several large universities I knew of, it wasn't uncommon for attendance at lectures to be effectively optional. The student was expected to do the homework, pass the midterm and final and maybe participate in discussions in a small section with a TA or graduate student. This varied from class to class, of course. Still, this was an incentive for a given professor to make their lecture interesting and useful enough that students wanted to attend.