I do not ask about special cases, e.g. supervisor does not approve the thesis, there is rivalry between the supervisor and the examiners and so on. Is there any general standard for viva, e.g. one needs to be able to answer 2/3 of the questions, etc.

I'm waiting for my viva, and I'm only worried about questions about related work. For example, my thesis only addresses a problem on deterministic programs, do I need to know all approaches to the same problem on probabilistic programs? (at the moment I don't).


I would like to emphasize again that I do not ask about special cases, e.g. plagiarism, wrong methodology etc. I believe theses cases are extremely rare. I just want to ask about a normal case where one managed to publish some papers, and advisor (happily) approved the thesis.

  • This depends a lot on the culture, country, school etc. For instance if I want to do my state exams, I have to pass all previous 5 doctoral exams, and also pass 3 additional ones on the spot. Failing to say anything there would cause me to fail the exam quite for sure.
    – yo'
    Commented May 6, 2015 at 9:26
  • 19
    The problem is that your "framing" is wrong: the special cases probably comprise the majority of cases when a doctoral defense "fails." If the thesis advisor is happy, and the thesis is acceptable, it is extremely rare for someone to fail.
    – aeismail
    Commented May 6, 2015 at 11:18
  • 1
    Perhaps you should ask your institution or adviser about how you are expected to prepare?
    – Superbest
    Commented May 6, 2015 at 12:23
  • Related: How would one fail a master thesis defense?
    – Wrzlprmft
    Commented May 6, 2015 at 12:50
  • 2
    Given your caveats about special cases, I think the most accurate answer to the title question is "nothing". Commented May 6, 2015 at 13:34

5 Answers 5


No, there are no general worldwide standards, other than "the examiners should be satisfied".

Your advisor is probably the best person to answer questions like this for your specific case.

  • 3
    Additionally, rules about what the examiners should be checking vary from institution to institution. Commented May 6, 2015 at 6:54

The following are some reasons that come to mind that might justify a failure in the viva:

For the thesis:

  • evidence of academic malpractice (plagiarism, etc.)
  • fundamental methodological flaws, such as a poorly chosen method or a misapplied method that calls into question the scientific validity of the thesis. My guess is that this is probably the most common reason for failure: that the work is just generally not a good piece of science and needs further development before it can be considered convincing.
  • a significant failure to engage with preexisting literature, which casts into doubt the significance and originality of the thesis' contribution to knowledge.
  • a general lack of academic substance such that the thesis is not of sufficient scope or novelty to merit the award of a PhD.

For the viva itself:

  • a general inability to answer questions about the thesis—to a such a degree that the examiners are led to question whether it is really the candidate's own work.
  • a significant deficiency in the candidate's knowledge of the literature, such that s/he cannot confidently be held to understand the relationship between his/her work and that literature.
  • a significant inability to justify the decisions made in the course of the PhD, calling into question the candidate's ability to construct a successful research project. For example, you should be able to say why you chose the approach you did, rather than some alternative.
  • repeatedly giving answers that are so severely wrong that they call into question the candidate's competency in the field.

The use of the words fundamental, significant, etc. in the above is quite deliberate. Examiners will forgive basic problems with the thesis or a somewhat flakey viva performance because they understand that passing the viva marks the start (rather than the end) of one's education. The option of minor corrections exists to deal with such issues.

  • One additional thing you should watch out for is a callous or inherent attitude towards the viva.
    – user34114
    Commented May 6, 2015 at 11:14
  • 5
    Most of these are usually failures of the candidate's advisor more than the candidate, as the advisor should never let an unready candidate defend...
    – jakebeal
    Commented May 6, 2015 at 12:02

I assume that the aim of a vivia is generally 'to establish whether the aims of the PhD program have been achieved', although I guess some will be more restricted than that (with another grouping checking the overall picture).

Therefore generally there won't be a specific question-proportion to pass, since there's no set list of questions. You need to demonstrate that you wrote your thesis, that it is right (well, close enough, since there will usually be some mistakes somewhere), and that it is of a suitable standard. You probably also need to demonstrate that you've engaged with the professional development part of the program (as a PhD student you are essentially an apprentice professor/researcher). You should know stuff about your field other than your immediate thesis question, you should know how the research community works, and you should be able to communicate your ideas (in writing, in a planned presentation, and in answering questions). Having some realistic plans for the future might also not be a bad idea.


As a former PhD student, now lecturer, it's very rare to hear of one failing a PhD viva. The most common outcome is to grant the PhD subject to minor corrections, which will be checked off by the internal examiner. Occasionally candidates will have to make major corrections for review by the external examiner, and much more rarely, candidates will be told to revise and resubmit where the process may or may not include an additional oral examination. Only the last outcome would be generally regarded as "failure".

In the first instance the student's advisor would not recommend/allow (depending on the institution) the candidate to go forward for a viva unless the work was to the standard required. In many universities, this means publishable in whole or in part, and making a non-trivial novel contribution. One way to satisfy yourself about these criteria is whether you've published anything at all to date: if you have, it answers the question that the thesis is publishable at least in part. It's very hard to "fail" (see above) if these basic criteria are met.

About related approaches, you would probably be expected to have a rationale for choosing your own approach. This would imply that you know your chosen method well, and know enough about the others to be able to make a comparative choice. E.g. if you were working in electromagnetics and chose the Finite Element Method to solve a Partial Differential Equation, you would probably want to be able to point out why you rejected Finite Differences and/or Analytical methods. But I would not expect you to be able to discuss the intricacies of Finite Differences in any great detail. The working knowledge you already have of your own approach and that of others is probably quite sufficient, as long as you can provide a strong justification for why you chose the methods you did. It's quite OK to justify based on ease of use, local availability, expediency etc.


Further to Nate and Jessica's answers, you can get an idea as to what the risks are in your institution and your subject area by asking around for examples of people who have failed their viva.

'Failing' is also relative: the 'do not darken our doors, no option to resubmit' outcome is only likely to be a risk in case of plagiarism or moral turpitude. The difference between acceptance pending corrections (regarded as a 'pass') and asking for a 2nd viva (often regarded as a 'fail') may not be huge in terms of the amount of effort on your part that is required to satisfy your examiners.

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