I will soon defend my PhD in social science in Sweden. I want to ask what questions the evaluation committee will ask me during the defense? If they ask me some questions outside my thesis, what shall I do? Is it enough only know well my own research? What quality I need to successfully defend my PhD?
Generally speaking, PhD defenses come in two flavors, and it is not possible to say a priori which one yours will fall into:
- A real thesis "defense" focuses on the thesis, and all questions will relate to the scope of the research work. In this case, knowing your own work and its context well enough should be sufficient, but it is of course possible that somebody asks you why you used method A rather than B. In this case, saying that you don't know B may not fly as an answer. However, you should not get a completely disconnected question just to test your general subject area knowledge.
- A "Rigorosum" (dict.leo translated this for me to "doctoral viva", no idea if this is a well-known term) is a general final exam for a doctoral candidate. Typically, this will also include questions about the disseration, but anybody in the exam commission is free to ask about other topics in the field as well. Typically, the questions are getting "easier" (more high-level) the farther they are away from the topic of the dissertation. The claim here is that a fresh PhD should have both, depth and breadth in her/his knowledge.
There are a number of ways to figure out which class your defense will fall into:
- Attend other defenses. Typically, PhD defenses are public, and it is highly recommended that any PhD candidate should visit a few before her/his own, to get to know the procedure and get a feel for what the defense talk is supposed to look like.
- Ask your advisor. The advisor should obviously know what the requirements of the defense are, exactly.
- Look it up in the programme description. Usually, the programme description will contain exam regulations for the defense, and this should describe the exam procedure and who is supposed to ask what kind of questions. This approach has two dangers: (1) you may misunderstand what the exam regulations are saying - as they are more legalese text, you may misunderstand the gist of it, and (2) the actual exam may happen differently than specified - there is no telling whether the exam regulation exactly captures the real spirit of the defense. Hence, you should really also talk to your advisor and/or attend other defenses as well.
Some types of questions that often come up:
Questions about some detail of your work. The point of such questions is often not so much the correctness of this small part of your dissertation, but rather to get you to demonstrate your ability to explain what you've done. This also helps to balance out the presentation, which typically covered the whole thesis in much less detail. For example, in mathematics you might be asked to go over the proof of one of your theorems in detail. Since you've spent more time working on these details than any of the examiners, and assuming that the examiner hasn't spotted a substantial error, you should be in a good position to answer such a question. Don't panic and assume that you've made some huge mistake, but rather go through the material carefully and convince the examiner that you're correct.
What are the broader implications of your work? This is actually a hard question for most students to answer because they've been so focused on the details of their thesis that they may not have taken time to see how it fits into the broader picture of progress in their discipline. This will also be an important question when you eventually interview for faculty positions.
Can this method be applied to some other problem Y? You may be asked how the techniques used in your dissertation could be applied to a different problem. If the answer is that the technique doesn't extend in that direction, then you should be prepared to explain why not.
Questions about what exactly is new in your work. You should have been extremely careful in writing your dissertation to properly cite earlier work and distinguish your new contributions from that earlier work. If this isn't clear to the examiners, you may be asked to clarify.
I attended about a dozen PhD defenses and recently defended my own PhD. Based on my (very limited) experiences, questions can be roughly categorized into two types:
Knowledge: the first set of questions or statements are usually to test your knowledge on your topic, the related work and whatever you have written down in your thesis and/or papers. If you have done all the work, these are mostly fairly easy to answer and are your way to demonstrate the awesome work you have done. These questions are to clarify, justify and frame your work related to others, in order to get a solid understanding of your contribution. Examples:
- Can you explain what you mean with #concept you introduce#?
- Why did you categorize or describe #your concept# in this way?
- I believe #your topic# relates to #other guys theory# in such a way, which introduces an interesting contradiction. Can you comment or elaborate on this?
- What is the main limitation of your work, and how could you address it?
Reasoning: committee members may also ask provocative or even harsh questions to see how strong you believe in your work but also whether you can transcend your topic and reason on a higher level. These questions or statements can be directly related to your topic but can also be more general. These types of questions are usually given to see how well the candidate performs when put under pressure and when they are questioned about things beyond their thesis. These can be interpreted as "nasty" questions, but remember that you can turn the questions around to your advantage. Examples:
- Why do you believe this is science? What is science?
- You spend #x# years researching this? Why did you choose the topic and why should we and the community care about it?
- I don't see the contribution in your work, can you explain?
- Why do you think you deserve a PhD?
- Why did you choose this specific application domain?
Again, this is based on my personal limited experience, but it applied to my PhD defense as well.
You do not have much influence on the questions from the committee. If your PhD studies were more or less normal and you got that far, everyone wants you to succeed. They will not ask anything incredible (if they are relatively normal as well).
As for the public questions, my experiences are :
the friends you gave questions to. You have to choose the ones who have good reflexes to jump up and down when time for public questions come. You also have to train the "what a surprising question look"
the odd colleague who decided to ask a question about something related to your field, but far enough for you to have no idea. You sweat a lot, visualize him hanging on a tree and hope for the best. Best is to answer whatever you know on the subject and everyone acts happy. If he persists then you ask him what is his view on the subject so that he sits down ashamed mumbling "I have no idea"
finally the 173 years old professor who absolutely wants you to discuss his article from 1952. You thank for the question and talk about the article from 2012 someone wrote on a related subject.
(events described above actually happened to me in the course of my 2 hours defence)