Can a reference (not self) be over-cited? I am proof-reading a student's PhD thesis and I find that the student repeatedly cites one reference, up to 40 times in one single chapter alone.
I suspect that this reference is an influential work and provides a lot of material but I feel this is too much. Apart form the obvious advise (don't cite as much), what effective strategies can one use to reduce the number of citations e.g. comment at the start of the chapter that &quot;this chapter builds on the foundational work \cite{ref} done by Prof X...&quot;
Can a reference be over-cited?

Assuming you are using in-text citation, it is necessary to cite the reference in-text every time you use information from it.  So, there is no upper limit on the number of times a reference should be cited.  Increase the number of citations until there is no ambiguity, and then stop.  40 times is not that many.
In most styles each reference is only listed once in the reference list.