In many ways, being a PhD student is a wonderful and amazing thing, but given the above, humane PhD advising is called for -- not harshness or rigidity.
Here are seven principles to consider, if you are a PhD advisor, or maybe to hope for in a PhD advisor, if you are student.
(1.) Don't take more than a month to return comments on written drafts. We advisors have a lot to do -- the book contract, the grant deadline, the trip to Germany. But it's our responsibility to give our students comments in a timely fashion. Next month will be busy too, and putting it off won't actually reduce the overall load unless you are slow enough to discourage students from showing their work very often (and I don't think that's what we should normally want). Taking three months to return comments risks slowing down your student's progress by a whole semester. The student might not prod you. They might say it's fine, no hurry -- but take that with a grain of salt, given the power relations. Find the time.
(2.) Don't assume that your student wants to be a superstar researcher. If you're supervising PhD students, you probably see the academic world through the lens of research, and you probably esteem other professors in your field mostly in proportion to the strength of their research. It's great if one of your students lands a job at a research university! It's good, but nothing special, if they land a job at a non-research-focused teaching-intensive university. If they end up teaching at a two-year community college, well, that's maybe a disappointment? Of course some students do really want top research jobs and really would be disappointed to teach at a community college. It's kind of in the air, in grad programs, that a research career is the ideal. But not all students want that. Most of world's professors work in teaching-intensive schools rather than powerhouse research universities -- and that's great. I love to hear it when students tell me that they'd rather teach community college than land a job at Harvard. If you assume that all of your students want to be superstar researchers, you contribute to a competitive and high-pressure environment in which teaching careers are devalued, students who don't appear to be on a research-career trajectory are perceived as disappointing, and students may not feel comfortable honestly sharing their non-research career goals with their professors. All of this unfair and disheartening. (Of course, it's terrific when a student aims for a stellar research career and achieves it. I'm just saying don't assume that's what your students want, and don't push those expectations on them.)
(3.) Don't pressure your students to work more quickly. Sure, the university might want to see them finish in five years. But you should be the advocate of your students' interests against the university, rather than vice versa. Life happens. Depression. Writer's block. Parenthood. Second thoughts and half-pursued career changes. Financial trouble. Illness. A rare and exciting opportunity to see Brazil with their sister. The situation is stressful enough for them without their advisor's giving them time pressure too. You might think it's in their interest to work more quickly; and maybe it is. But rather than take a harsh or paternalistic approach, pressuring them to work faster "for their own good", let them decide what pace works for them. With perfect neutrality, help them finish quickly if that's what they want; and let them take their time if that's what they want.
(4.) Remember that your student is already excellent. It is so hard to gain admissions into a good PhD program these days that only excellent students are able to do so. They might not know how to write a dissertation yet, and they won't have as deep an understanding as you do of the research methods and the existing literature in your subfield. But I've yet to meet a PhD student who didn't have the potential to be a terrific scholar and teacher. There's no need for weeding them out or trying to figure out who are the strong vs. the weak ones. Instead, help each of your amazing students more fully realize the excellence they already have.
(5.) Evaluate the work, not the student. Evaluation is the constant duty of a professor. But focus your evaluation on the student's work rather than on the student's ability or overall quality. Excellent scholars sometimes produce mediocre work, especially when they're under pressure or trying something new. No biggie! (Reminder: Your student is under pressure and trying something new.) If a student feels that everything they produce will be evaluated as a sign of their genius or (more likely) lack of genius, the atmosphere will be one of anxiety, pressure, perfectionism, defensiveness, and competitiveness. Eventually, of course, the core parts of the student's dissertation will have to be excellent, but that's at the end of the PhD program. Assuming that your student is a human being, their work along the way will have its ups and downs, and some of it will have to be discarded or will need at lot of revision, especially if they're creative, adventuresome, and open to risk. How are they going to get helpful feedback if they feel that you are so constantly judging them that they dare not show you material unless they feel it's already near perfect?
(6.) A hoop is just a hoop. A class is just a class. A draft is just a draft. Help them move efficiently through requirements (without pressuring them to do so (#3)). The standard should be adequacy rather than exceptional brilliance. If your student feels a need to prove their genius at every step, it should be no surprise if they're stressed out, taking incompletes, prepping far too long for their quals, etc. Since they're already excellent (#4), if you've been a good advisor and if too many uncontrollable life changes haven't happened, their dissertation will be excellent at the end, when it's finished (#5).
(7.) Be ever mindful of the asymmetry of power. The extreme asymmetry can be easy for advisors to forget, especially for those of us who regard ourselves as egalitarians and who like to be on a friendly, first-name basis with our students. What you "lightly" request might be experienced as compulsion. You might casually criticize, or tease, or razz them as you would a peer, but the effects of such casual remarks can be much more devastating, disruptive, or disorienting than you realize. If a full professor says to another full professor working in the same field "that's obviously wrong" or "that's stupid", that might just be an occasion for friendly disagreement; not with a student whose whole career depends on your opinion.
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All of these principles are defeasible, of course. They represent my perspective on being a humane PhD advisor. I might be wrong, and I might be much less humane than I think I am or than I hope to be. (My grad students say they find me to be a good advisor, but given the power dynamics they might feel compelled to say that. Few of us really know, I think, how good we are as advisors.)
One disadvantage of my adherence to (7) above, I suspect, is that I'm less chummy with my students than some other advisors are. Socializing, inviting students to my house, sharing details of our personal lives, etc., feels slightly strange to me given the power dynamic -- is the "friendliness" free or compelled? I feel like I can't know, and that uncertainty keeps me always slightly guarded and formal. I can only hope I'm not too standoffish as a result.
One disadvantage of my adherence to (2) and (5) above, I suspect, is that the stronger students receive from me less of an encouraging vibe of "you're the best, you're going to be a superstar researcher" than they might hope or expect. All my students are excellent and I prefer not to rank them in my mind. Before anointing one as the next research superstar, let's see how the dissertation turns out in the end. Nor do I especially value research excellence over teaching excellence.
When I think back on how warm and friendly and encouraging my father was with his strongest students (not PhD students in his case, but Master's), I somewhat regret my restraint in both of these respects. There is, I suppose, no perfect solution but instead a range of tradeoffs that can reasonably be weighed differently.
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Related:
Against Those Year-End Faculty Meetings to Discuss the Graduate Students (June 17, 2014)
Think of Your Dissertation as Your Longest Work, Not Your Best Work (July 19, 2018).