I myself may some day wish to do a Ph.D. I have sometimes thought about if I would want to choose a theorist or academician whose work and whose personality I gravitate towards, even if I am not certain if I would stay exactly in their subfield my whole life. I think there are some good examples of theorists who do a Ph.D. under a particular scholar, yet then gravitate into a related but different field, or even pioneer a new topic on their own.

So, is it more important to do a dissertation on a topic you are extremely keen on, and worry less about who you are doing it under, or is it quite an advisable path to do a Ph.D. under someone you connect with or think highly of, even if the topic matter is either less hyper-specifically that professor’s expertise, or if you do not actually plan or care to stick to that niche topic for very long? Because I believe just working under a seasoned mind can rub off on you, so it’s natural to want to study under a mind you hold in high regard.

Or are both valid?

  • Related: academia.stackexchange.com/questions/203847/… Commented Feb 7 at 1:59
  • Closely related canonical question: (How) Can I switch from field X to field Y after getting my PhD? Commented Feb 7 at 17:28
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    Partly that's a choice we cannot shield you from: It depends why you pursue and what you want to do with your PhD. (That you ask this question makes me think that you are not burning for some specific research question though!) Commented Feb 7 at 21:20
  • What do you mean by "choose a theorist or academician"? As your supervisor? Commented Feb 8 at 8:25
  • You will have at this point a hard time predicting where your PhD project will go, and what subfield you want to work in when it's finished. You are certainly not bound to the subfield in which you did your PhD. But then if you know somebody's work and like it, this doesn't automatically mean the person is also good for you as a supervisor. Furthermore there is also strong variability regarding how close a topic somebody supervises is to their current (visible) research. So much depends on factors that can't be assessed at this point. Contact potential supervisors and talk with them! Commented Feb 8 at 10:35

11 Answers 11


I'd like to reach "behind the curtain" and pull out an aspect of the PhD which often confuses potential applicants. A PhD can look like anything else "students" do at a university: you sign up to X years of pain study where domain experts throw knowledge at you, walk you through practice, and send you off with a shiny piece of paper saying Now You Know Stuff.

This illusion can be costly. A PhD looks like a degree just as a snake looks like a legless lizard. But here's the fangs: a PhD is also your first academic job, and thinking about it like a job instead of a degree can make decisions significantly clearer. Critically, while it takes lots of hassle and paperwork* to change the course of a degree, changing course during your PhD (or your postdoc!) is much more like changing jobs, or perhaps taking an internal transfer.

Take for example "should I follow the topic or the supervisor?" Well, think about applying for jobs: would you rather do work which fits your interests exactly under a boss you don't quite like, or do work you might struggle with under a great boss? There's no one answer, but that's the point: it's really a decision about choosing your workplace, and you should think about your worker-personality to answer it.

Or "what if I need to change my PhD topic halfway through?" Well, again, imagine that you're working as an accountant, but halfway through you discover a hidden passion for ... underwater basket weaving. Or something. How would you go about exploring your new field and changing careers? Some people would drop everything and leap. Others would slowly make time to explore new options, dipping one toe into the water at a time. Again, there's no one answer: the point is to reframe the question.

Hope this helps. All the best!

*mostly unnecessary, to me, but that's a different story ...

  • 8
    Absolutely correct. For most people, a PhD is not only their first academic/research job, but the only research job they will ever have: most professor jobs are teaching jobs.
    – Cheery
    Commented Feb 7 at 15:13
  • 3
    I guess it depends on the field, @Cheery, but in mine and related ones, it is a minority of Ph.Ds who go on to be professors, and virtually all of those do at least one postdoc first (so at least one other research job). Even considering that some leave the field altogether, I'm pretty sure that a majority spend their careers holding bona fide research jobs, some in academia and some in industry. Commented Feb 7 at 21:26
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    +1 for a PhD is also your first academic job. When I was PhD, the successful students in our program treated it like a job (some went as far as only "working" from 8-5 and also had work life balance). Also, I would say that could be broader and that "it is a job." Commented Feb 8 at 14:16
  • @Cheery and John -- I'm sure it's very field-dependent. Certainly we would serve PhD students better by not just saying it's a job, but by opening their eyes to all the other jobs they could do out there after their PhDs! Commented Feb 8 at 23:09

There is no single golden path to follow here.

If you stay in academia (and that is a big "if"), you will need to demonstrate your independence from your advisor or mentor at some point in time. It's fine to do your postdoc in a related field to your Ph.D. thesis, but at some point in time you do need to branch out and pursue new avenues, because academia is evolving, and is not interested in people rehashing their subject over and over again over their entire careers.

On the other hand, if you switch subfields or fields immediately after your Ph.D., then you are gratuitously giving up much of what you built up over your Ph.D. time - all the specific knowledge, all the network, all the contacts your advisor could leverage to help you. (Make no mistake: contacts are hugely important in academia.)

It makes absolute sense to do a Ph.D. in a field you do not plan on staying in for the long haul. Ideally, you would keep this thought in the back of your head during your Ph.D. Try to keep a finger in the pie that does interest you. Read the "other" field's publications. If possible, make contacts there. Perhaps do a side gig or a collaboration. Bonus points if you find a way to combine your current and your target field in some way.

Also, think about when you want to have a conversation with your advisor about this long-term plan. This is probably not something you want to bring up when you interview for the Ph.D. position. But once you have established yourself and still plan on switching fields at some point (you might change your mind halfway through the Ph.D., after all), and have a good rapport with your advisor, it might be useful to talk to them. Some advisors might feel a little miffed if you left the field all of a sudden, but might have been helpful if you had told them earlier. After all, the advisor themselves switched fields at some point in their career (see above) and might have some advice or (again) contacts that might help your next steps.

My wife did her Ph.D. in a subfield and using methods (EEG and fMRT in specific phobia) that she hasn't touched since (her postdoc was about genetics, now she is doing immunology and cell energetics in PTSD and related disorders). I did my Ph.D. in discrete optimization and am now academia-adjacent in forecasting.

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    not interested in people rehashing their subject over and over - Freeman Dyson apparently said that "if you want to win a Nobel Prize, you should have a long attention span, get hold of some deep and important problem and stay with it for ten years". Did academia change in the intervening time between then and now?
    – Allure
    Commented Feb 7 at 2:34
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    @Allure: (1) 10 years is not your entire career. (2) Beware of selection bias: let's not look at what Nobel Prize winners say they did, but at what happens to "normal" academics who followed this track. Yes, I do believe that if you apply to a professorship, and your research output is all about the one topic you did your Ph.D. on, then you will at least need to explain why you never did anything different. Of course you might just have found that one deep problem that is worth spending your entire career on. But you will need to convince the committee of that. Commented Feb 7 at 7:22
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    @Allure I think few would consider making Nobel-worthy progress on a deep problem over an extended period of time as simply rehashing a subject over and over. Unproductively sticking with the same topic for another 10 years after one's major contribution is a different matter, of course. See also this question for some takes on the value of not getting stuck and comfortable in a single area of research.
    – Anyon
    Commented Feb 7 at 7:55
  • 1

There are three main purposes to the PhD candidature:

  • Gain broad knowledge of your field at a PhD level;
  • Gain expertise in a specific topic in your field (the topic of your dissertation) at a PhD level;
  • Develop research skills sufficient to allow you to create and publish academic papers and related outputs.

Only the second of these is significantly affected by your choice of dissertation topic, so even if you do your dissertation in an area that you later don't practice in, you should still have developed good broad knowledge of your field and research skills for practice.

For purposes of generating a career in research, it is useful ---but not crucial--- to have selected a good topic for your dissertation. Selection panels for positions mostly look at your research record overall, and also whether your research interests will fit well within their institution/department. There are some academics and researchers who do their dissertation in a topic that they later don't practice in. (In some cases, the PhD degree is sufficiently traumatic that the person is sick of their topic and does not wish to return to it later.)

  • Purpose 1's importance is subject specific. That is, while some research supervisors/external examiners and topics may demand that a PhD student deepen his/her general knowledge, others do not. Fundamental discipline principles and how they pertain to sub-areas other than that being researched, sure - and expect viva questions to test this.
    – Trunk
    Commented Feb 7 at 16:51
  • Very important: learn to think (and address problems) at PhD level. (the reason it is called a philosophical doctorate). Commented Feb 8 at 19:05

This is a US perspective and it may not be quite the same elsewhere.

The purpose of a PhD is to gain broad knowledge of the general field and deep knowledge of a particular aspect while producing one or more publishable works. This implies learning the research and publishing process in the field. Often in many fields it is a first work. In some fields publishing is required. But that is the general idea.

There is no expectation that a graduate has to stay in the same subfield throughout their career, but most people do for a few years at least. If one can obtain a tenured position then changing sub fields and perhaps even fields is more tenable.

I changed major fields once (math -> CS) and minor fields many times through my long career.

But it is good to work with someone you can learn from. Nice if they are prominent. Even nicer if you actually have common interests. Still nicer if you have some insight into the key features of the subfield. You want to learn the craft and you want to get a boost in your early career. After that the world opens up.

Note that if everyone "stuck" to their doctoral topics forever, there would be very little academic/scientific progress.

Prepare a base. Work from that base.

In some parts of Europe and maybe elsewhere, it is assumed that a candidate already has the "broad" part covered, likely in a masters program. And even the US view isn't uniform as most places set their own policies and standards. But at the end of it, breadth, depth, and publishable research are pretty standard.

  • Moreover, in some parts of Europe and maybe elsewhere, a Ph.D is considered a desirable qualification for a career in engineering or business. Commented Feb 7 at 14:36
  • @MichaelKay Desirable, perhaps, but hardly a requirement. But do you really think most professional software engineers have a Ph.D?
    – Barmar
    Commented Feb 7 at 16:07
  • @Barmar Of course they don't. But those that do tend to stand out above their peers, in my experience. Commented Feb 8 at 8:41

Aspect 1:

PhD's are hard work. So if you, as a person, have a "hard-work ethic" regardless of the work, then being "keen on the topic" may not matter much for the chances to complete the work. But if you are the kind of person that needs to get enthusiastic about something in order to work hard on it, then "being extremely keen on the topic" could become critical.

Aspect 2:

Why are you doing the PhD? For the love of research? For the love of being able to teach at the higher level? As a professional avenue towards academia/industry/government, where income and/or prestige considerations play an important role for you? If some subset of these together, each to what degree?

If professional considerations loom larger, then strategic thinking is called for: you may want to take up topics that appear to be in fashion, with a supervisor that appears well-established (and has a reputation for seeing their supervised PhDs to completion), in an institution that has some respectability.

If love of science and/or teaching is your thing, you may want to find "a mind that you hold in high regard" to study with, as a priority consideration.

To state the apparent contradiction, Science is an Art - and as there are Artists, there are also professional Artists. It would be useful to clarify to yourself into which category you mostly see yourself belonging, even if as a current assessment, that may change in the future.

  • 2
    Although a topic that is clearly in fashion now is unlikely to be in fashion 6 years from now.
    – Jon Custer
    Commented Feb 7 at 15:42
  • @JonCuster True, and not true. In 6 years it will likely return to fashion. :) Commented Feb 8 at 2:11
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    Also not all great academics are great supervisors Commented Feb 8 at 19:06
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    @PauldeVrieze Certainly. As with the distinction/gap between being a good researcher and being a good teacher. Commented Feb 9 at 11:13

I am currently in the process of doing a PhD, so my answer may change in the future.

  1. You must work with someone you like.

In a world where you do industrial job instead of academics job, this may not happen frequently, and is not THAT needed. But in academics, since things are much harder, and your advisor is pretty much your "second family", you must work with a guy you are comfortable with.

You should appreciate him, think highly of him, and you can get constantly inspired by him. If you find such a professor and he likes to work with you, you should go for it.

I know that you can always learn from people, but different professors have different styles. I mean, they are all smart and hardworking, but they are different in nature. Some professors just don't want to do things deeply, as long as it can be published in a journal he thinks is enough, it is enough. Some professors are full of ideas but need YOU to figure out the details, and they don't like working on the details, so if you want to show them your detail, they may be disinterested.

You need to find a same type of person, or a person you want to become. So, if you find the person, you should go for it. This is really important. Imagine if you working with someone, when you ask a technical question, they can't answer or don't care to answer, but you are really into techinical details? You guys will torture each other for the next five years.

  1. About what if you are not that interested in that subject.

I think that whatever the subject it is, once dig deep enough, it is always interesting. The common feeling we have "oh that's not that interesting" is because we are in the phase where we already dug a little, so we already know a little, but we deeply know that once digging deeper it would not be this easy anymore. So, we always have this

"interesting" ---> "nah" ---> "oh this is actually quite deep, i love it".

Yeah, there will be some subjects you just genuinely not interest in. In such a case, you can never be interested in it. Then, I really doubt that you will also like that professor. If you indeed do, that will be a tough decision. I don't know what to suggest.

For me, I am really technical and like focusing on details. I also tend to dig really deeply at a point on the knowledge surface (which is not, in general, a good habit). I also need constant feedback, and really frequent communication, yeah, you can call me insecure. So, I need an advisor who also like thinking deeply, doing technical stuff, and like talking to me, like doing Q&A often, etc.

I am really happy that I found my "perfect match" in this PhD program. Also, I really respect him and I think that he is the best professor in terms of teaching and research I have ever met. Every time I talk to him I am so excited. He also appreciates me, thinks highly of me, which really boosts my confidence to challenge myself more. I start to expect more from myself, so I work more and harder. You see, then you enter into a positive cycle. In particular, luckily for me, he is also working in the frontier of the field, so I don't need to worry about if I am working on something that no one cares.


To add another perspective - it also depends on the region/country where one is getting a PhD, as well as on the University policy and the supervisor's views. A few examples:

  • In eastern Europe PhD is formally defined as being able to conduct independent research. This made it notoriously hard to pass the PhD defense and produced quite a few people who formally finished their post-graduate studies, but defended their PhD thesis many years later (if ever.) This is also often a source of conflicts between eastern European postdocs and their western supervisors - about who determines the direction of research.
  • In the US PhD students are often expected to prove themselves by working independently on a research project, agreed upon with their supervisor, who may provide more or less help. I have not heard about many people failing to pass a PhD defense, but for some it takes more years to get to this point, and there is a significant proportion of dropouts.
  • In Western Europe a PhD student is often expected to follow the supervisors' instructions, sometimes on a day-to-day basis. In turn, the supervisors take to it as teaching a course, where they have to cover a variety of topics: calculations methods, research subjects, literature review, etc. This results in graduates who are (IMHO) less prepared to carrying out independent research, but who have a very wide range of skills, which make them well-prepared for finding a job in industry (a difficult step for PhD graduates in the US.)

As I said, these are not an absolute rule - I have seen different approaches practiced by professors working in the same university department - some throwing a talented student in water, and seeing whether it can solve a challenging research problem, the others patiently guiding their students from A to Z.

  • 2
    My Western European experience is quite different from this. I expect more independence even from my MSc/BSc project students and supervise accordingly, let alone a PhD. I have also seen this elsewhere. It may strongly depend on the subject matter (I know about Stats&Math.) Commented Feb 8 at 10:28
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    @ChristianHenning I have seen some students (in France) being literally told what to do today, what to do tomorrow etc. This was not a general rule, but rather common. My observations in Germany were indeed different - but that was in a Max Planck establishment, I don't know how it is in universities. Yet, as I said, tight supervision has its positive sides - students left to themselves may muster to perfection a specific subject or set of techniques, which may be good for carrier in academia, but not for transitioning to industry.
    – Roger V.
    Commented Feb 8 at 10:34
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    There is quite some space between telling people what to do from day to day and "leaving them to themselves". Commented Feb 8 at 10:38
  • 1
    @ChristianHennig sure, these are two extremes. Still, there is an obvious trade-off between the levels of supervision and independence.
    – Roger V.
    Commented Feb 8 at 10:43
  • There are too many country differences, but a 3 vs 4 year PhD is quite a difference and entry points are not quite comparable. Commented Feb 8 at 19:12

I'd say firstly choose a topic of genuine interest - be it academic interest or industrial application interest - since the X years commitment to low-paid and often frustrating work must be sustainable morale-wise.

Choice of supervisor is equally crucial for a bearable PhD programme - just look at all the posts to this forum about bad supervisors.

So choose someone who has a genuine record of respectable research over several years and not someone who may be a huge name in the field.

The supervisor must be someone with whom you can have good two-way communication - someone who hasn't lost their initial enthusiasm for observation, investigation, conceptualization and rationalization.

For even daughters of the swan can share

Something of every paddler's heritage


Unless you're financially free, the ultimate purpose of a PhD is to get a job.

I don't know how familiar you are with job searches, but it's broadly true that transferable skills matter more than direct expertise. The latter does matter if the job is exactly on that topic, but the chances are pretty good you'll be working on something different than your thesis topic. Here're some examples:

  • You really love the topic now, and it turns out you still really love the topic after you've started working on it. That passion is a deciding factor in you generating high-quality results, and it leads to you graduating with a sterling PhD. Afterwards it turns out that funding agencies like your particular topic, so they fund research (i.e. issue grants) in it, making you a highly valuable commodity.
  • You really love the topic now, and it turns out you still really love the topic after you've started working on it. That passion is a deciding factor in you generating high-quality results, and it leads to you graduating with a sterling PhD. Afterwards it turns out that there's a major discovery in an adjacent field, such that funding for your topic dries up and much of the new funding goes there (recent example: gravitational waves).
  • You really love the topic now, and it turns out you still really love the topic after you've started working on it. That passion is a deciding factor in you generating high-quality results, and it leads to you graduating with a sterling PhD. But during your PhD you also fall in love, and you don't want to subject your partner to the nomadic lifestyle that comes with being a postdoc. The only academic jobs in your local area are not related to your topic.
  • You really love the topic now, but after you've started working on it, you realize it's not a bed of roses. You generate high-quality results anyway and graduate with a sterling PhD, but afterwards when you're looking for a job, you look for something else.
  • You really love the topic now, but it after you've started working on it, you realize that academia is not a bed of roses. You find you hate writing funding proposals, most of which are unsuccessful (but very time-consuming); or perhaps you hate the publish-or-perish culture. You decide you'd rather take up a non-academic job.

In most of these cases, "I know what gravitational waves are, how they are generated, how to detect them ..." is nearly irrelevant, but "I know how to program in Python" is a big deal because it's transferable.

In other words, your thesis topic is significantly less important than what transferable skills you learn during your PhD. You're better off prioritizing other things (prestige of university/supervisor, location, proximity to friends/family, etc) than the topic, especially since there's a real chance you'll change your mind on the topic once you learn more about it.


First, it's definitely possible to change your topic/field. But be aware that this likely needs to happen during, not between jobs. (As @Shern Ren Tee points out, academic positions are just like other jobs.)

Consider applying for a new (academic or industry) position doing Y, while having worked on X...Your chances of getting the position will probably be low. Not because you could not show your competency with your previous job, but because it takes years to get deep into topics, but you are expected to produce results (e.g. papers) right away.

In other words, be sure to get a position in which you have the freedom to explore into different areas.

Second, having a great Ph.D. advisor is important. But if you reach into topics outside their area of expertise, you will not benefit from their domain knowledge. On your own, it can takes years to get a grasp of the state of the art in a field, so your Ph.D. might take longer than if you stay in your advisor's field.


It is really a balance of both, although others have said treat it like a workplace, also treat it as your education. You are training for a specific job, what skills do you need to do that job? Will your PI have the resources to help you get those skills, will they be supportive and focus on your education and not just turning out more papers? I switched labs because I had an unhelpful PI that wasn't an expert in my research focus, it was painful to get through the learning curve, but not as painful as her giving me inconsistent expectations, berating me, and still NOT being helpful toward my education. I enjoyed the research, but she definitely killed all joy I had for any science related topics. Switched labs and I have more resources and opportunities to learn, a PI that is knowledgeable and helpful without being a dick, and other students that will help me out when I have questions (in the other lab I was siloed as the only person in that specific field not necessarily bad labmates, we're all still friends, they just didn't have that background). Never regret my decision to leave, I'm much happier, have even have more opportunities and better career outlook because I'm not afraid my PI is going to be a dick and try to fuck me over.

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