How to Answer Viva Questions You Do Not Know the Answer To

The question is not always a test of knowledge

Every viva includes at least one question the candidate cannot answer immediately. That is a design feature, not a failure. Examiners choose questions that push at the edge of what the candidate knows, because that is where they can see how a researcher thinks (Trafford & Leshem, 2008). How to answer viva questions you do not know the answer to is a technique, not a memorised list.

The technique has three parts: acknowledge, reason aloud, and name what is missing. Candidates who do all three land the answer even when they do not know the finding. Candidates who reach for a plausible-sounding invented answer lose the room, because examiners read fabrication more reliably than they read hesitation.

What examiners are actually testing

Mullins and Kiley (2002) interviewed 30 experienced examiners across five universities and found that panellists rate reasoning under pressure as one of the strongest signals of doctoral readiness. Kiley (2009) frames the doctoral viva as a threshold event: the candidate crosses from “student who knows their work” to “researcher who can hold their work up against questions no one has asked before.”

The implication is direct. When the panel asks a question you cannot answer, they are not testing whether you know the answer. They are testing three things: whether you can name the boundary of your knowledge, reason from what you know to what you do not, and hold the answer at the right level of uncertainty. All three are skills; all three are rehearsable.

Step 1: Acknowledge, do not fill

The first move is to name the state of your knowledge without reaching for filler. “I have not looked at that specifically” is a real answer. “That is a good question” is not. Filler phrases signal that the candidate is buying time to fabricate, and examiners hear that before the candidate does.

There are three acknowledgements that consistently work in the room:

• “I have not read that paper, but I can tell you what the argument would need to show for me to update my position.”
• “I have not looked at that specific subgroup in my data. Here is what the surrounding analysis suggests.”
• “I do not know the answer to that. Here is how I would find out.”

Each acknowledgement opens a route forward. Filler acknowledgement closes it, because the panel now has to ask a second question to move the conversation.

Step 2: Reason aloud from what you do know

Once you have named the state of your knowledge, work from what you have to what the question asks. This is where examiners see reasoning under pressure. It is also where a real answer to a question you could not answer directly often emerges.

The move is: identify the nearest thing in your own thesis to what the panel is asking, and work outward. If the panel asks whether your finding holds in an older cohort you did not study, reason from the mechanism your finding relies on. Does the mechanism plausibly hold in that cohort, or does something about the older cohort change it? You have not answered the empirical question, but you have shown the panel that you can think about the empirical question with the tools your thesis has already built.

Rugg and Petre (2004) describe this as one of the “unwritten rules” of doctoral vivas: examiners reward candidates who work at the edge of the thesis rather than pretending to work beyond it. The reasoning does not have to reach a conclusion. It has to be visibly grounded in what your thesis actually establishes.

Step 3: Name what is missing

The third move is naming what your reasoning cannot settle without further work. This is often the answer the panel wanted. “To settle whether this holds in the older cohort, I would need to run the same design on that cohort and check whether the mechanism produces the same effect.”

Naming what is missing is not weakness. It is calibration. Examiners rate calibrated candidates more highly than confident ones, because calibration is what a research career requires (Wisker, 2012). Candidates who name the exact study that would settle the question are showing the panel that they know what the research programme around their thesis looks like, not just what the thesis itself contains.

There is a further move that closes the answer well: connect what is missing back to your contribution. “The extension I am describing is exactly the follow-up study my discussion chapter frames as next work.” That connects the answer to your future-work section and shows the panel that your thesis already anticipates the question they just asked.

What not to do when you do not know

Two failure modes come up repeatedly, and both are avoidable.

The first is fabrication. A candidate who invents a result, a citation, or a claim they cannot back up is telling the panel something they will not forget. Bhattacharyya and colleagues (2023) documented the same pattern in AI-generated academic content: plausible-sounding claims that fall apart under a specific check. Examiners run those specific checks in the room.

The second is deflection. “I did not have time to study that” is honest but incomplete. It does not tell the panel how you would think about the question, only that you did not think about it. The complete version is “I did not study that specifically, but here is how the mechanism I did study would apply.”

Where Thesisroom fits

The technique above is rehearsable. What it needs is a supply of anchored questions that push at the edge of your thesis, not generic viva questions from a public list. Thesisroom’s mock viva coach reads your thesis and generates examiner-grade questions anchored to specific passages. The questions include ones designed to press at the boundary of your evidence, where the acknowledge-reason-name move is exactly what a strong answer looks like.

The full method treats this rehearsal as a whole-degree seat, running from the first chapter draft to the finished thesis. The point is to hear the difficult questions in rehearsal, so the technique in the room becomes reflex.

Frequently asked questions

Is it okay to say “I don’t know” in a viva?

Yes, when it is followed by reasoning. “I do not know, but here is how I would think about it” is a strong answer. “I do not know” as a full stop is a partial answer that leaves the panel unable to gauge your thinking. Examiners reward the reasoning after the acknowledgement, not the acknowledgement alone.

How long should I pause before answering a hard question?

Five to ten seconds is normal. Repeat the question back if it helps you think, or ask for clarification if the question is genuinely ambiguous. What is not normal is a fifteen-second silence followed by filler. Short pauses signal thought; long ones signal panic.

What if the examiner asks about a paper I have not read?

Say so, then reason from your thesis to whether the paper’s likely argument would change your position. “I have not read that paper. If the argument is X, my position would need to accommodate Y. If the argument is Z, my position is compatible with it.” That answer shows the panel that you can locate the paper in the argument even without having read it.

Should I guess if I am not sure?

No. Guessing at the level of “I think the answer is...” commits you to a position you cannot defend. Reasoning at the level of “here is what would have to be true for X to be the answer” leaves you room to move as the panel presses. The second is more honest and more defensible.

Can I take notes into the viva?

In most systems, yes. A marked-up copy of the thesis and short notes on key claims are expected. What is not expected is reading prepared answers off a page. Notes are for finding the right page, not for reading paragraphs.

How do I rehearse for questions I cannot predict?

You cannot rehearse the specific question. You can rehearse the response pattern. The Mock Viva Coach generates questions anchored to specific passages of your thesis, including ones designed to push at the boundary of your evidence. Rehearsing the acknowledge-reason-name move against those questions makes it reflex.

One takeaway before you close this tab

The candidates who handle hard viva questions well are not the ones who know everything. They are the ones who name what they know, reason from it to what the panel asked, and end by naming what is still open. Rehearse the three-step move against questions drawn from your own text, and the version you deliver in the room will be steadier than the one you deliver in your head. Thesisroom’s mock viva coach is where the anchored rehearsal lives.

References

Bhattacharyya, M., Miller, V. M., Bhattacharyya, D., & Miller, L. E. (2023). High rates of fabricated and inaccurate references in ChatGPT-generated medical content. Cureus, 15(5).

Kiley, M. (2009). Identifying threshold concepts and proposing strategies to support doctoral candidates. Innovations in Education and Teaching International, 46(3), 293-304.

Mullins, G., & Kiley, M. (2002). ‘It’s a PhD, not a Nobel Prize’: How experienced examiners assess research theses. Studies in Higher Education, 27(4), 369-386.

Rugg, G., & Petre, M. (2004). The Unwritten Rules of PhD Research. Open University Press.

Trafford, V., & Leshem, S. (2008). Stepping Stones to Achieving your Doctorate: Focusing on Your Viva from the Start. Open University Press.

Wisker, G. (2012). The Good Supervisor (2nd ed.). Palgrave Macmillan.