It depends on the program. If you are in a lab in a team doing funded research, you might get very little say in the choice of topic.
Otherwise, in many programs, learning how to come up with a suitable topic is one of the skills you have to demonstrate. Your supervisor might be a good sounding board and help, but choice of topic is your responsibility.
As to the question of how, start by asking people and talking about their ideas. Other than that, here’s the short answer:
Another thing, if it's your first time, don't expect to make a ground-breaking discovery. You'll be successful if you understand the topic well, learn the research process without making mistakes, and come up with a finding that adds to current research.
First, if you don't choose a good topic, your chances of graduating with a PhD are slim. Here's what could happen:
If you need permits, funding, or ethical clearances, you need a proposal before you start research.
A research proposal specifies the purpose of your research. You can express your research topic as a problem to be solved, as a question to be answered, or as a hypotheis to be tested. Your conclusion will be the solution to the problem or the answer to the question.
A focused question helps you to plan your research, do a focussed literature review, know what data to collect, ignore irrelevant information, and come up with a result. Otherwise you will review lots of literature and collect lots of data, but then have to throw most of it out because it doesn't help you to achieve your particular purpose.
It's a chicken and egg situation. You need to read to find a topic, but you need a topic to select items to read.
The research needs a specific purpose, and the need for the research is expressed as a problem that needs solving. Without a clear and specific purpose, you would not be able to plan a solution nor know if you have achieved it.
A specific research question will also save you time and effort from reading many things that won't be much help. It might also save you from throwing out many pages of writing that took a lot of time and effort to write, but that are not helpful in answering your narrowed-down research question.
Do a thorough literature review that includes current research. No short cuts there. It will give you a good idea of what has and has not been done. (Having said that, it's always possible that someone somewhere has done something and nobody has noticed.)
Next, when you discuss your topic with faculty members, they will advise you and won't accept a proposal if they think the topic is not unique.
You can't. In fact, it is quite likely if the topic is important and others are aware of it. Things to do about it … Work faster because a slow research can be overtaken. Update your literature review. In some fields you might even have to adjust your topic.
Various. The following come to mind.
First, it must be within the abilities of the institution to supervise and assess, given that it may co-opt personnel from other institutions. This usually rules out many topics that students might like.
Second, it must be feasible. If it’s not actually possible, then students won’t be allowed to try.
Third, it needs to have an intellectual challenge, which normally means a contribution to the theory of the field. This rules out many “how to” practical topics, but the border is sometimes not very sharp.
Fourth, it needs to be a new contribution to knowledge. In some institutions, this includes critical reviews as long as the critique produces something new and leads to a particular conclusion. Other institutions don’t allow critical reviews at all.
Some topics clearly have no potential for a passable dissertation. The reasons? Try these:
“Complex” is often used to avoid explaining something that one doesn't understand or is too lazy to explain.
If something is “complex” it usually refers to a phenomenon affected by lots of different factors (e.g. cause, effects, assumptions). The research would presumably comprise description and analysis. That is, define (or at least describe) those factors and say how they relate to each other. The phenomenon might vary from case to case. (See “grounded theory,” which is a methodology designed for this kind of problem.)
Another factor is eidetic. That is, how do you know that it is only one phenomenon to be analysed, not multiple phenomena that look similar?
The list of relevant factors could be very long but let's make a start. Consider these:
There is no specific formula. The way to do it is to anticipate what it will involve and how complex it will be. This requires some experience; one cannot anticipate what will be involved in a particular topic if one has never taken a research project through the whole cycle. It is also a judgement call.
Having said that, many PhD students seem to look at dissertations of other students. The limitation is that they then tend to choose similar research problems and use very standardised methodologies.
These things are helpful in estimating the length of a dissertation:
If your methodology is documentary analysis, the introduction and conclusion chapters might be fairly standard, but all the contents will probably not follow a standard outline. Try writing a tentative outline as a rough guide and discuss itith your supervisor. However, be prepared for it to change quite dramatically when you learn something new.
Let's call the two ideas A and B.
First, do you have a good reason to suggest that A is related to B? If so, you can ask the question, “What is the relationship between A and B? Do they correlate, or does one cause the other?” This could be a good research topic.
However, if you have no good reason to relate them, you might be taking yourself into a trap. One of the requirements for a topic is that you have one topic, so you cannot write a paper on it. You might do research on A or on B, but not one research on two unrelated topics.
This question has come up in another form: “What is relevance in an academic project?”
“Relevance” is an interesting word. It has often been used in a sense that was very unclear. For the word to be clear, I suggest that it needs an object; in other words, “relevant to what?” These have similar meanings but seem to me to be clearer:
Yes, but it must be different. If it is in the same specialised field, it will most likely be an extension or development of the Master's thesis.
First, an undergraduate thesis is more of an introductory writing exercise. It is not expected to make a significant contribution to knowledge.
Second, in most cases, a longer document is more complex than a short document. As a rule of thumb, a paper of double the length is often much more than double the complexity of a short paper. This indicates a greater contribution to knowledge.
There are several ways to answer this:
Having said that, you can't be totally sure because you don't yet know the answer to your question. Your research might hit a snag or shift sideways in ways that you cannot anticipate.
First, let’s assume you’ve done your background reading. Then try these steps:
Note: This will also be helpful for all sorts of other things, e.g. when you have to write your background statement, saying how the problem came about, when you decide on methodology, etc. The reason is that they must all align.
I'm assuming that you gave an area of interest in your application without giving a specific topic.
Your first job is to get a good idea of expectations. You'll learn these partly by reading the institutional documentation. There'll be policies but probably also other guidance material. You also need to get an idea of the unwritten rules, which you get by talking to academic staff. As Pugh and Philips have said, the nature of “original contribution to knowledge” is a moving target and not usually spelled out clearly, but you can't get a PhD without knowing what it is.
Second, it is a good idea to read several past dissertations from your department. However, don't be overawed by them. They were not at first written that well; they are result of previous not so good drafts that were then edited into something better.
The next thing is the reading stage. You need to read all the major relevant works in your field and recent relevant research to get an idea of a topic. (Keep notes; you don't know what might be useful later on.) During your reading, you should be able to firm up your ideas on several possible topics and narrow it down to a particular topic and then refine it.