Most students think that you have to come up with the “perfect” dissertation topic. And there is no perfect anything, of course. What you want is something new to say about an old topic, really. You want a topic that will draw on all kinds of theories, assertions, research, and analyses of another scholar, researcher, or intellectual. Why? Because you will have to fill some 300 pages and you want more voices in there than your own, believe me.
In fact, you might begin by thinking of your dissertation as a way of doing the following thing, instead: A way of working your way into the extant scholarship with a stance of your own ON the extant scholarship.
Now, insert yourself in the critical discussion on said topic with a theory of your own. For example, Shakespeare’s plays have been in existence for some, what, 500 years now, right?
Would it be easy to say something completely new about this author—no. Instead, you would have to find your way into an already extant conversation on Shakespeare. For example, post-colonial theory looks at the influence of different pressures on a novel written by either because they are writing from the perspective of being a victim of a colonized nation or the pressures on their literature from being the colonizers themselves. There has long been a discussion on post-colonial pressures in William Shakespeare’s plays and you could try to assess the extant scholarship and work yourself into it.
Or, you might have a new theory on workplace conflict management, which draws on the theories of others and rejects a lot of other theories in the process. You want to find a way to draw the dissertation out, widening it into a bigger picture, bringing in all kinds of theories—perhaps looking at the whole evolution of workplace management theorems as you go along.