History professor Hugo Schwyzer offers up one at Jezebel:
I don't have a problem with students asking out their former instructor, provided the grades have been turned in. But I try to warn them that the reality of an actual relationship is likely to be disappointing. Students fall in love with a fantasy; the professor who seems so cool and commanding in the lecture hall is rarely so charismatic over dinner — or as mind-blowing in bed as one might have fantasized. I've seen a number of student-teacher relationships unfold in which a woman ends up dumping her former instructor in near-disgust; the gap between what she thought he was and what he turned out to be was too much to bear. That can be shattering and disillusioning for everyone involved.
Two decades in the classroom have taught me that when it comes to students and teachers, we don't get crushes on people whom we want sexually as often as we get crushes on people whom we want to be like. Yes, some crushes are purely physical. But more are what I'd call aspirational: the objects of the crush represent something students want for themselves. College is an uncertain time; good teachers tend to embody passion and certainty, two things students desperately want. And when they're crushing on a prof, young people are usually confusing the messenger with the message. As I learned the hard way many years ago, rather than encourage the crush to feed our egos, our job as professors is to turn that intensity back on to our students, encouraging them to use their newfound enthusiasm and let it take them to all sorts of wonderful places. Places other, of course, than their professors' bedrooms.
This is all absolutely true, but the principle extends beyond the classroom, no? That is, I am hard-pressed to think of infatuations that I've felt that weren't aspirational, that weren't deeply about something other than the crush that I wanted for myself. And if one were to follow Schwyzer's advice literally, then one would probably wind up never dating anyone at all. I suppose that nuns have long life expectancies and all, but for the rest of us, it's often worth it to assume the risk. I suppose professors and students might be a special category where this sort of problem is particularly likely to be acute, but that's somewhat different from saying that actually dating all aspirational crushes should be avoided, which seems to be what Schwyzer's saying here.