How to survive a thesis defense
The thesis defence or viva is like an oral examination in some ways. It is different in many ways, however. The chief difference is that the candidate usually knows more about the syllabus than do the examiners.
Consequently, some questions will be sincere questions: the asker asks because s/he doesn't know and expects that the candidate will be able to rectify this. Students often expect questions to be difficult and attacking, and answer them accordingly. Often the questions will be much simpler than you expect.
In a curious relativistic effect, time expands in the mind of the student. A few seconds pause to reflect before answering seems eminently ...view middle of the document...
If the nightmare ever did come true, and some questioner found a question that put something in the work in doubt... mind you this is thankfully very rare.... then what? Well the first thing would be to concede that the question imposes a serious limitation on the applicability of the work "You have identified a serious limitation in this technique, and the results have to be interpreted in the light of that observation". The questioner is then more likely to back off and even help answer it, whereas a straight denial may encourage him/her to pursue more ardently. Then go through the argument yourself in detail - showing listeners how serious it is while giving yourself time to find flaws in it or to limit the damage that will ensue. In the worst caese, one would then think of what can be saved. But all this is hypothetical because this won't happen.
What usually happens is that the examiners have read the work typically twice, and looked closely at some parts that interested them most. These are usually the good bits. The examiners have standards to uphold, but they are not out to fail you. (Administratively, it is a lot more complicated to fail you than to pass you!) In general, they feel good about the idea of a new, fresh researcher coming into their area. You are no immediate threat to them. They have to show that they have read it and they have to give you the opportunity to show that you understand it (you do, of course). And they usually have a genuine interest in the work. Some of them may feel it is necessary to maintain their image as senior scholars and founts of wisdom. Judicious use of the "Good question", "Yes, you're right of course", "Good idea.." and "Thanks for that" will allow that with a minimum of fuss and a maximum of time for champagne drinking.
If one of the examiners is real nasty, your thesis defence is probably not the best place and time in which to do anything about it, except perhaps for allowing him/her to demonstrate his/her...