Argument and lecture.

I always learn so much more from an argument than from a lecture. It's kind of like vision, I think. You see better with two eyes than with one. Why? Because each eye sees a different picture. With info from both, your mind can interpolate a single picture that couldn't have been seen by either eye alone. Voila. Depth perception.

This has particularly applied in my recent study of economics and the climate controversy. I learn an enormous amount about how the issues work and play together by hearing disagreements ... because my mind is forced to build a deeper, more nuanced picture than either side alone could have provided in a lecture.

If I were going to run a university, I think I would structure classes with 2, rather than 1 professor. And the class would be structured around controversial (and ostensibly interesting) issues in the subject. And each prof would argue his own perspective. In the process, they would have to explain the basic elements of the subject. To make it comprehensible. As a result, students would gain a much deeper, profound understanding of the topic, as well as the modes and ways of analyzing and criticizing ideas.