Taking courses beyond requirements in a Ph.D. program As I'm starting to look to put together my plan of study, a question popped into my mind: are there, generally speaking, rules against taking additional courses beyond what is required for a Ph.D., or is it simply frowned up by most advisers (in the interest of creating more time for research endeavors)? I ask because I've found several graduate certificates offered at my university that seem relevant to my interests (in teaching), and I'd like to take an additional 2 or 3 courses to fulfill their requirements.  I've heard from other grad students in my lab, however, that there is frequently push back from our adviser on such matters.
As an adviser, I encourage my graduate students to take classes they find interesting and/or that broaden their knowledge and therefore are useful to later finding jobs. Ultimately, my goal in this is to help my students become well rounded and broadly educated graduates who will be successful in life. The only caveat I place on this is that they need to make sure they have enough time to do the research that will ultimately lead to their thesis and their defense.

I don't know whether I'm typical in this, but would imagine that most advisers will agree to let their students take other classes if a student asks and gives a reasonable justification. I think most will even agree to this if the student is paid from a grant.