External dissertation committee members?

In our newest "how can we help you?" thread, a reader writes:

PhD student here. What are reasons for and against having a dissertation committee member who is not part of your department? How do you go about inviting a professor from another department to be on your committee? Should you be working with them first/already, or at least be acquainted with them? What are the odds of their acceptance if you ask them? Are there any drawbacks to asking?

These are great questions. I imagine there are two different types of dissertation committee members who are not a part of your graduate department: committee members from other universities and committee members from a different discipline at your own university (e.g. psychology, political science, etc.). In both cases, I imagine there are two main reasons to want an external committee member like this: (1) to draw on their expertise, and (2) get another recommendation letter for the job-market. I'm not entirely sure what reasons there are against having external committee members, though, nor am I at all sure what the process looks like for seeking one out. Do any readers with experience in these matters have any tips to share?

Comments

[FC]

At the school where I got my PhD, we were required to have an external committee member. The graduate school set the terms: four members, at least two tenured/tenure track, at least one from a different academic unit. My external reader came from the law school.

The grad school allowed exceptions when the department chair thought this necessary. Appeals went through the Dean's office.

My dissertation director recommended a few external readers. I contacted one and he agreed to help.

At my school the external reader's role was largely to ensure the legitimacy and/or adequacy of the dissertation. This wasn't about content, as such, but more about whether the project is substantive enough for a PhD, and whether the work was actually completed by the candidate.

I'm sure many external readers offered feedback to candidates, but mine did not, and we were not troubled by this. My dissertation director and one of my committee members gave me a lot of feedback. The other committee member gave me some feedback. Again, everyone thought this was fine.

At another school, one I had attended earlier, PhD committees were made of 3-4 department faculty. We could request an outside reader but their inclusion had to be approved by the department members on the committee first.

[m]

Every school has a different system. Where I was, generally, the committee that worked with you on your dissertation were from the department. BUT, the committee that examined you included someone from another department on campus, and an external evaluator, a philosopher from another university. That person had veto power - they could vote you down single-handedly.
There was little incentive for people in other departments to work with students on their dissertations unless they really were working on their topic. In that case, the student usually knew the faculty member already - from going to their colloquia, etc.

[PhD in OZ]

I had someone from another university on my committee, and made the connection when they were a long-term visitor at my university (that university had a LOT of long-term visitors, though, so this might not be generally useful advice). I know several other people who had their advisor introduce them to someone who would be a good fit at a conference, and after the student and the other academic talked for a while I believe the advisor made the ask.

[Assistant Professor]

Like FC, my PhD program required an external member on all dissertation committees (and the graduate school had all sorts of other conditions, regarding composition of committee).

For me and most of my fellow students, our outside readers were not closely involved in the project as it developed and did not provide ongoing feedback, but instead received polished drafts of the prospectus and dissertation, respectively, and participated in those defenses.

What you need from an outside reader will depend on your situation. If you want someone with content expertise that your department might not be able to offer, and/or who can provide ongoing feedback then you should make this clear when approaching someone. I think many people are willing to be outside readers because it is a relatively small lift, so if you want/need something else from this person then make that explicit at the outset otherwise it might be a disappointing relationship for all parties.

In addition to contributing content expertise, an external reader can be a way to add prestige to your committee -- and if they get to know you well enough can be a helpful letter writer (but see paragraph above, they might not know you or your work that well depending on your relationship with them to provide a helpful reference).

Internal/primary mentors go a long way in helping line up an outside reader and this shouldn't all be on the student to figure out. Even if your other committee members don't personally know your wish list of potential external members (which will be more likely if you need the external person to bring content expertise outside of philosophy), having the request come from a committee chair who can also say nice things about you and your work, ad well as nice things about the external person and their work, is often helpful.