If I were a Spanish Major as an undergraduate and decide to pursue a PhD in a completely unrelated field (like Theoretical Physics), it makes sense to give a qualifying exam to check that I had the necessary skills to begin the program. But if I'm coming from a B.S in math to a PhD program also in math, it doesn't seem to make sense to give a qualifying exam, as if the knowledge I gained in my undergraduate was insufficient. I presume that one is accepted into a PhD program because he/she has already demonstrated the "qualifying" skills. Thus, I'm baffled by the notion of the qualifying / prelim exam. I'm curious about the ultimate goals of these exams, and how they relate to the professional development of a graduate student.
There are two main reasons:
- as a "sanity check" to make sure that the student you've admitted is really the student you thought they were; and
- as a weed-out tool, in case you've admitted more students than you have spots for in PhD projects in a given department.
Both purposes are significant. The second is the more unfortunate, and could generally be reduced through better selection processes and through better deployment of teaching and research resources and funding within a department. The former use is equally important, in that it makes sure that students don't try to "coast" their way through what the department believes is its core curriculum that students need to know.