How to Prepare for a PhD Viva (Thesis Defence)

The viva feels like an exam, but it works differently. By the time you sit it, the examiners have read your thesis and formed a view. The viva is where they test whether you understand your own work, can defend your choices, and can think about it critically. Candidates who prepare well usually find it a serious, but constructive, conversation.

What examiners are actually deciding

• Is the work yours? Can you explain every part of it, including the parts done with collaborators or tools?
• Is it original and significant? Do you know what is new compared with the closest existing work?
• Is it sound? Are the methods appropriate, the results valid, and the conclusions supported?
• Do you understand its limits? Can you name the weaknesses honestly before they do?
• Are you ready to be an independent researcher?

A preparation plan

Four to two weeks before

• Re-read your whole thesis, ideally on paper, and mark every claim you must be able to defend. Note any typos, inconsistencies, or numbers that do not match, and know the fixes.
• Read your examiners' own recent papers. You will not agree with everything, but you will understand their perspective and likely questions.
• Make a one-page map of the thesis: the contributions, the chapters, the key results, and the weak points.

Two weeks to one week before

• Write a two-minute and a ten-minute summary of your thesis, and rehearse them aloud without notes. Nearly every viva opens with “summarise your thesis”.
• Write answers to the standard questions (below), then compress each to a few sentences you can say naturally.
• Do at least two mock vivas with people who will interrupt and push back. A supervisor from another group is ideal.

The last week

• Re-check logistics: the room or video link, a printed thesis with tabs, water, a notepad.
• Practise drawing key figures, equations, or architectures from memory. You may be asked to use the whiteboard.
• Sleep. A tired candidate answers worse than an underprepared one.

Questions to rehearse

You cannot predict every question, but most fall into a few themes. Prepare a short, honest answer to each of these:

1. Summarise your thesis in two minutes.
2. What is the main contribution, and what is new compared with existing work?
3. Why did you choose this method over the alternatives?
4. How do you know your results are not due to chance, bias, or leakage?
5. What are the main limitations of your work?
6. If you were starting again, what would you do differently?
7. What are the implications, and what should be done next?
8. How does your thesis chapter differ from the paper you published on it?

Answering well

• Pause. Taking ten seconds to think is fine.
• Answer the question that was asked, then stop. Do not fill the silence.
• Concede fair points. “That is a valid limitation, and here is how I would address it” earns more respect than defensiveness.
• Do not bluff. If you do not know, say so, and explain how you would find out: “I am not certain. My understanding is X, and I would check Y.”
• Point to the thesis. “I discuss this in Section 4.3, where I show...” shows command of your own work.
• Use the whiteboard for derivations, architectures, and timelines, and ask for clarification if a question is ambiguous.

After the viva

Outcomes typically range from acceptance with no changes, through minor or major corrections, to resubmission, depending on your institution's rules. Most candidates receive some corrections, and that is a normal part of the process, not a failure. Write down the examiners' feedback straight away while you remember it, agree a corrections plan and timeline with your supervisor, and then look after yourself. You have earned a break.