Doing research in the space between disciplines is hard work. But this does not seem to discourage very many people, especially PhD students, from making the attempt. A great many dissertations combine theories and mix methods, probably on the assumption that pluralism is a good thing, and that a single perspective is too limited. When I talk to students about this issue I always try to push back a little on that assumption. Adopting multiple points of view is not a good thing in and of itself. Researchers should always ask themselves what a proposed additional point of view will make possible. Why is the approach of an established, unitary, well-defined discipline not enough?
Here it is important also to distinguish between kinds of interdisciplinarity. Some scholars take great pride in working (and some pains to work) outside any established area. They bring two or more theories together that have never been combined before. Or they apply a novel mix of methods. Or they test a theory using a method no one has tried before. Or they interpret a particular kind of data with a theory that is normally applied to another kind of data set. This is very difficult to pull off, in part because the novelty of it precludes the existence of good “exemplars” (in the Kuhnian sense of completed work). Also, there is no clear audience to consider, no well-defined readership.
That’s why I always recommend doing interdisciplinary work within an established, as it were, inter-discipline. Don’t try to invent a new combination of hitherto uncombined approaches, especially if you’re a PhD student. Instead, look for an interesting community of prospective peers that are already combining some of the approaches you are interested in. Learn from them, not just the details of the individual theories, but the means by which they can be combined. From a social, rhetorical point of view, this is not very different from working in a classical discipline. There is a standard to work to, and there is a body of received knowledge to learn. It takes discipline.
If you try to define your own unique interdisciplinary position, the only people you can turn to for guidance are in the disciplines you are moving between. All too often, you find them too tolerant to learn anything from. Your understanding of their theories and methods may be merely adequate, and they may not comment too much on it but then turn around and speak enthusiastically about the use you are making of the other discipline, though they don’t know enough about it to criticize you. The same thing might then happen with members of the other discipline. What you lose is critical feedback. You come to work in an environment where you’ve given no one the authority to tell you that you’re wrong. This can be exciting in the short term, but is not very satisfying in the long run.