All the three types of research revolve around an argument, a thesis. They of course differ in terms of student level, that is complexity.
But, what makes a bachelor's thesis different from master's and PhD theses in terms of procedures of researching given that all of them may follow the same process of research, questions or hypotheses, review of the literature, methodology, results and discussion?
The PhD thesis should be on a much higher level than the Honours/Masters thesis, offering a contribution to human knowledge that is of a sufficient level of "significance" to warrant publication in a respected journal.
Significance is highly subjective, and you also do not necessarily have to publish to be awarded the PhD (sometimes the peer-review delay means that they come out afterwards, or there may be some intellectual property issues that make it beneficial to refrain from publication). It is awarded based on your supervisors consent and a review of academics in your field. So the "significance" would probably be judged by them in terms of how much original work they see as a reasonable expectation at that stage of your development (first 3 years of serious/committed research). Unfortunately it also means that some people who probably do not deserve PhD's are awarded them anyway for fulfilling grunt work for their easy-going supervisors.
It is possible that some Honours/Masters thesis might even be more significant/higher quality than a PhD thesis. Unfortunately, this does not mean that the submission of the thesis will award the degree that they deserve. The university may have a policy to upgrade the student's enrolment if the supervisor senses that such progress is being made. However, it is impossible to upgrade to a PhD without completing Honours and I believe nearly every single university has a policy of a minimum period of enrolment before submission is allowed. A subsequent question that you may have is how to gain a PhD without enrolling in one, which is another level of achievement completely.
As for the difference between Honours/Bachelor and Masters it would depend on your university, but both have no requirement for publication quality research and are usually small tasks/ideas that are not worth the supervisors time to think about alone, or involve a lot of labor. In fact, in my school, many Honours thesis are of a higher level than the Masters, because the smart Honours students will either graduate into the work force or go straight into a PhD. The Masters students are usually those who cannot find a job and are not suited to research. However, I believe some other universities may require a mandatory Masters degree to start the PhD.
You may get a better idea by looking at some titles/abstracts of completed theses. The PhD level will be something like a new method/observation/application whereas the Masters/Honours will be an application specific set of measurements/simulations or even simply a literature review to gauge the needs of future work. The word limits are also typically different (although note that quality is NOT proportional to the number of words), with PhD at 100K, Masters at 50K and Honours at 30K at my university.
Go back to basic definitions... In history of university degrees (500 years ago)
A bachelors degree is about learning existing knowledge. Historically from the book(s) written by the univ staff.
A masters degree, after you have learnt what is already known and in books in your topic area, is about learning evolving knowledge - that is near recent and current literature in academic journals and conference presentations.
A doctorate degree is about creating new knowledge by research.
So it is now easy to understand a thesis/dissertation for each degree.
A bachelors degree should be a critique of existing knowledge, often looking for inconsistencies in view points from different sources and synthesising arguments or positions in a DISSERTATION )that is you disserting !
A masters thesis (thesis is Greek for 'I believe') can be either an assembly of new knowledge from new published research or simply a critique and integration. It might have propositions (not hypotheses) that the masters student offers as a conclusion from bringing together new knowledge from different sources.
A doctoral thesis is where the author undertakes research, usually collecting primary new data which is presented as both factual findings and conceptual findings and thus new knowledge in the form of a new model or theory. Also possible, is to challenge existing knowledge and show earlier published knowledge is invalid.
Well that's what they all should be. In practice there is some overlap and different universities and faculties have their own custom and practice. It all starts to break down about 40 years ago when a masters degree become post graduate in time rather than post graduate in level. Thus engineers with a bachelor degree might take an MBA to make them more employable and did more a less a bachelor degree in business in 18 months rather than 3 years as they were already a graduate.
But still thinking in the above categories can help students today focus on the overall agenda.
I have examined over 55 PhD theses. And several hundred masters theses and I base my approach to assessment on the above.
Prof Peter Woolliams, B.Sc(hons), B.A., PhD, Emeritus professor, Anglian Ruskin College Cambridge, U K
Roughly speaking, there are three levels of tasks:
For a Bachelor's thesis, you would only expect 1 and 2, that is the student should do something (e.g. solve a well-defined problem) with the knowledge they have aquired during their studies.
For Master's thesis, you would want to have a non-trivial amount of 3, that is the student should transfer the competences aquired during studies to new problems. This usually includes (more) extensive literature research.
A formal difference that (imho) derives from the above is volume; Bachelor's theses typically award less credits than Master's theses and should thus take up less time and fewer pages.
