Thanks to commenter Laura (last week) for reminding me that I've been meaning to muse about the "thank you" part of a thesis / thesis defense.
When I was in grad school, a prominent faculty member (who was department chair near the end of my grad years) made it known that he hated the "thank you" part of the thesis defense and strongly discouraged students from including any sort of personal thank you in their talk. If someone really wanted to, they could have a very brief and professional acknowledgment at the end of their talk (not the beginning). His reasoning was that the defense is an exam, and it is not the place for a long acknowledgment of the emotional and other support provided by significant others, relatives, pets, or faculty. Most students respected his wishes and confined their acknowledgments to the thesis document or to giving a speech at a party or other social occasion to celebrate a successful defense.
More typically, the thesis defenses I have seen involve acknowledgments -- some at the beginning, but more commonly at the end. I am not as extreme as my former professor, but I am glad when this part of the talk is short. It's always weird to listen to a long emotional thank you to the spouse and dog, and then go straight from that into exam mode.
I certainly don't mean to dismiss or underestimate the importance of friends and family in a graduate student's life and career, and yes I know there are uncaring, uninvolved advisors. That imbalance will lead to a student's wanting to thank the people they like, and not thanking the person who inflicted stress, pain, and suffering on them (or who neglected them) for an extended period of time.
Even so, students who feel that they were poorly advised and who therefore don't want to thank their advisor for providing a research opportunity and funding that led to a graduate degree nor for reading manuscripts and thesis chapters and writing letters of reference, should at least not be rude to their advisor in front of the rest of the department. I personally think that would be rather childish and unprofessional, though of course those traits are not necessarily obstacles to success in life.
I have seen cases in which an advisor did care a lot, spent a lot of time (years) helping a student, provided lots of valuable research experiences (and funding), wrote a lot of letters of reference, and helped the student launch their career, and yet, during the defense-acknowledgment the student just quickly listed the names of committee members, including the advisor, and then spoke at length about how wonderful their spouse and fellow grad students are. Well, that's special, of course, and it is more fun to thank your friends than your professors, but it makes me think that even successful, reasonably non-paranoid students have no idea how much time their advisors spend on activities that directly benefit the student, and how much support they have gotten from their advisors over the years.
My other hypothesis is that because the final throes of thesis completion can be stressful -- perhaps the advisor's comments on the final drafts of the thesis document/manuscripts were unwelcome for being either insufficient or too sufficient (or whatever) -- the student isn't feeling particularly positive about their advisor at the time of the defense. At the time of the defense, however, the defending student is feeling positive about the fact that they have made it this far, and are feeling grateful for how much help they got from their family and friends along the way, and so it is natural to focus on that.
I am not advocating that students get all sloppy-thankful at their defense about how much their advisors have done for them. In fact, a brief acknowledgment is sufficient and anything more would be inappropriate at the final exam/defense. However, unless an advisor is certifiably evil and depraved, it would be best to avoid sentiments such as "I thank Professor X and my committee. And now I want to thank those who really helped me." That is rude. [FSP's Guide to Academic Etiquette, Rule #342]
So, although many of us advisors might be willing to be understanding about not rating as high as our students' pets, especially cats, and do not begrudge Rover for being thanked more profusely than we are, it would be nice if students realized that their advisor probably had a fairly significant role in getting them to the point of standing in front of the room defending their graduate research.
9 months ago