[compsciphd]

huh? Maybe for "internal" committee. For my PHD defense, I had 3 internals and 2 externals and the externals could have been anyone my advisor approved of (in practice for me, I picked my committee and my advisor just rubber stamped it, perhaps because he was content with my choices)

[sramsay]

I'm talking about who can sign the forms that say you fulfilled the requirements of a degree. Random people cannot do that. Emeritus professors usually retain that ability.

I've served on PhD defenses where you had uncredentialed people on the committee, but who could not sign off on the degree.

This probably looks different to you if you're a student, because you typically don't see the paperwork that gets sent around afterward. But a diploma is a legal document. There is no "rubber stamping" of anything. Not if the school would like to maintain its accreditation.

[dagw]

externals could have been anyone my advisor approved of

Don't they at least need to have a at least somewhat relevant PhD? Where I live that is definitely the case.