When does a PhD end?

Question

When does a PhD end? I know this is a very general question on this forum, but let us consider a CS-engineering group. What is the usual and primary consideration for letting the student finish officially?

Is it the number of years spent, when the professor feels nothing more useful will come out of working on the problem (or of the student!)?

Is it the logical conclusion of the problem and the thesis? A student works to complete a problem in 3 years and publishes a couple of journal papers, and finds there is no more to the problem. Will he be allowed to finish or forced to work on some tangential problem simply to prolong his PhD?

Answer 1

As a general rule, my PhD students need to do two things to get a PhD:

• Publish 3-4 papers on a coherent topic, mostly in top-tier theoretical computer science conferences, including at least one paper without me as a co-author (and preferably at least one paper that was previously rejected).

• Jump a bunch of administrative hurdles: don't screw up classes, don't screw up TAing, pass quals, gather a committee, propose a thesis, write a thesis, defend a thesis.

That's it. In my experience, most PhD students do way more than this.

A couple of comments on the original question:

• Very few students "finish" their thesis topic. Equivalently: If a research question can be closed in just one or two papers, it's probably not a good thesis topic. Good research opens as many new problems as it solves.

• Reaching the point where further collaboration with a student is unproductive means the student-advisor relationship has failed. Sometimes students really do exhaust their research potential, despite their advisors' efforts; in my experience, those students usually don't get PhDs. (Most successful students reach "critical mass" long before they finish.) More often, this happens because the advisor isn't giving the student enough appropriate guidance.

Answer 2

Intuitively, I would say there are two "extreme" ways of seeing a PhD (at least that I know of):

• The point of a PhD is to solve a particular problem (e.g. show that P ≠ NP), and in this case, the PhD ends when the problem is solved, and the dissertation explaining the solution is written. I have known some (brilliant) people who solved some problem hard enough to be considered worth a PhD in 2 years, and who spent the rest of their PhD funding publishing more papers. But technically speaking, the PhD was finished after 2 years, the rest was more like a pre-postdoc.

• The point of a PhD is to train a young scientist to become a (hopefully brilliant) researcher. The topic could then be a just an excuse to work on a sub-field, and as any other training experience, the PhD is over when the advisor believes the young scientist is ready to move on. Of course, writing a dissertation is a good way to convince your advisor, but it could be the case that you have a rather "weak" dissertation (i.e. that won't dramatically change mankind), but a good publication record, external collaborations, etc. In this case, it's even possible to consider writing a Sandwich/stapler thesis.

I would say that most PhD are a mix of the two approaches (and it probably varies from a field to another, from a university to another, from an advisor to another, etc), and the vision can actually be different between the advisor and the student. Personally, I know that I was seeing my PhD more like in the first case (i.e. I wanted to solve hard problems), while my advisor was encouraging me to be more diverse, saying that I would have my entire career to solve hard problems.

Answer 3

Generally speaking, there are well established "mile stones" for the completion of a PhD. This typically comes in the form of writing a dissertation - either in book form or a series of papers - and the presentation (and defense) of those results to a committee of professors (and sometimes a general audience).

It is usually not "years spent" or exhausting a project's potential (or the students).

There are however often some established timelines to prevent students from defending their dissertation too fast - required coursework, certain timing restrictions etc. This is usually intended to keep a student from rushing their studies and meeting the letter of the graduation requirements, but not the spirit - that they be well trained in their field and capable of doing independent work. But if they meet that, and defend their dissertation, no one is going to make them "run out the clock" or the like.