The problem with this arrangement is that it emphasizes one particular and narrow view of what purpose college serves. Courses are seen mainly as steps in accreditation, as obstacle courses that students must run to demonstrate suitability for certain jobs. Online courses serve this function well, because they assess continuously: the student’s keystrokes, his underlining, even his time viewing each screen are all logged and analyzed.

There is no doubt that continual assessment can improve pedagogy: a teacher can catch and quickly remedy misunderstandings. However, one reason conversations like the one prompted by pistol shrimp are so deeply gratifying is that they have nothing at all to do with assessment or accreditation. They are not on the syllabus or the final exam. Rather, they are reminders that college serves purposes entirely unrelated to accreditation: courses prompt and equip students to investigate the world, leading not merely to a diploma and a salary, but to a more engaged life — not just to a richer bank balance, but to a richer existence.

But when the educational triangle is collapsed — when the outside world loses its stature as a full-blown third party — then you don’t take a course to understand the world, you take a course to succeed in the course. Education gets reduced to a testing and triage service.

The other reason to preserve the educational triangle is that it provides training for other, similarly configured pursuits. Scientific research, for instance, is both vitally social and directly empirical. Scientists attend conferences and read one another’s papers, but we also test the claims of others against our own experience and experiments.

To put it differently, we use one ear to listen to one another, the other ear to listen to the water. This is a crucial skill not just for scientists, but for any citizen in a democracy. To weigh the claims of authority against evidence that is not curated by that same authority; to forget, at least occasionally, about how one is being watched or assessed by that authority; to be skeptical and independently minded — these are vital abilities in a citizenry defensive of its own power, and I worry that students working inside a virtual world of their professor’s construction are learning to listen too much to the teacher and too little to outside evidence.

How can we claim the advantages of online education without losing that most essential, triangular configuration of higher education? One possibility, now being implemented in pioneering programs, is the hybrid online-field course. In the online environment, students read text, watch lectures and solve problems. They then meet their professor in the appropriate field setting — a museum; a nature reserve; a certain city neighborhood — and actively apply their newly developed disciplinary perspective.

This approach might give us the best of both worlds. Research has shown that the most effective teachers spend less time lecturing and more time engaging students in follow-up work. Early research on hybrid online-classroom courses suggests they retain students as well as traditional courses. In my experience, the field setting naturally fosters strong social ties, one key to assisting and retaining underprivileged students.