Among the very finest classes I ever took was Caltech's Physics X, taught by Richard Feynmen. No grades, no credit, no homework, you could ask him any question

Among the very finest classes I ever took was Caltech's Physics X, taught by Richard Feynmen. No grades, no credit, no homework, you could ask him any question you liked provided it was purely conceptual - that is it didn't require him to work out any math.