It seems like most PhD applications require at least two reference letter. One of my Master's thesis supervisors (a PhD) has written me a reference letter. Can I ask my other supervisor (a PhD student) to write me the second one, or would that be redundant?

The other alternative letter writers are all professors who have only seen me in class and can't really comment on my research potential.


I've sat on my department's graduate studies committee during application season, and so I can provide at least one point of anecdata for how PhD application recommendation letters are used, at least in my tiny corner of the academy. YMMV.

First, These letters are among the last things that are looked at. We don't have rigorous thresholds for grades, GRE scores, subject GRE scores, publications, etc. But all of those things are used to "objectively" sort the pool. First the obvious admits are skimmed off the top, and fellowship offers are made to some of them. This is the first place where letters are important, since quotes are mined from those letters to try and win funding for these students from the University (i.e., we entice the student with a prestigious award, and the department doesn't even have to pay for her!) The money quote is usually a ranking and/or direct comparison -- "In my twenty years at Giant State University, I've seen no more than 5 students of X's caliber. I would say her talents remind me of Y's at that age, who is now a professor at Prestigious U" -- and this is why even a mediocre teaching letter is more useful for this purpose than a nice letter from a PhD student (who can not be counted on to have a reasonable intuition for another's future potential).

Second, we work our way down to the marginal cases; this is much more difficult since the marginal cases require a more holistic take on the application package. No one gets immediately thrown out just for bad grades or a bad subject GRE score, but we expect some explanation of a mitigating circumstance (not an excuse!) in the personal statement, and hopefully reflected in the letters as well. For example, if you were dinged in the first pass for a low GPA, we would like to see that it was a bad first year (and not a bad fifth...); that you are on an upswing. If you think you might be a marginal case for whatever reason, the letter from the PhD student might be helpful -- perhaps you don't have any publications, but the PhD student can vouch for your work and verify that you have something in preparation, or explain why your project failed (projects often fail!) but that nonetheless you mastered some state-of-the-art technique on the way.

On the other hand it is a big waving red flag if those things are then not pointed out by your actual boss (the PhD holding supervisor). If you think the student will write a better letter, then you're probably best off having that student lobby on your behalf with the professor, to make sure the professor's letter is strong, and then get a second letter from someone else.

I would strongly recommend you do not ask for a letter from a non-academic unless it was an actual research position (and even then, these can be iffy if the supervisor has no letter-writing experience). On occasion we see glowing letters from a student's supervisor at their summer construction job, or a call center for a political campaign. Well-rounded students are great, but such letters are almost useless.

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  • I wouldn't restrict things to "actual research positions." For example, in engineering, I would give a letter from a professional engineer substantial weight. In fact, some of the best letters I've seen have come from non-academics. (Writing good letters, furthermore, is not the exclusive province of academics! And some academics can't write very good letters, either.) – aeismail May 25 '13 at 19:19
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    These letters are among the last things that are looked at. — Then your admissions procedures are very different from mine. We don't admit anyone without strong letters. – JeffE May 26 '13 at 5:11
  • @JeffE: I understood that sentence as meaning that other factors are first used as a filter, rather than that they actually admit anyone without looking at their letters. – Tara B May 26 '13 at 7:52
  • @TaraB: There's a big difference between "among the last" and "not the first". – JeffE May 26 '13 at 19:28
  • Fair enough, @JeffE; although we should be careful with what we mean by "strong letters." I've certainly seen students accepted who had steller credentials, but I thought the letters were "weak" in the sense that the writer had no idea how to write a reference (or the student made the mistake of asking a famous person who has never actually interacted with them). We certainly would be wary of students, regardless of credentials, if the letters were negative in their content. This is not what I typically mean by a "weak letter". – wsc May 27 '13 at 2:53

The main point of the letters of recommendation are to comment on your abilities, and to place them in the context of other people the recommender has known and worked with. The better they can comment, and the larger the number of people the recommender has worked with and therefore can compare you to, the better the recommendation will likely be.

For this reason, it is not nearly as helpful to get a letter from a PhD student as from someone who is more experienced and has likely worked with more master's students. On the other hand, if the option is to get a letter who can only comment on your class work, I would opt for including the PhD student's recommendation letter.

However, if you have had a non-academic person (perhaps an internship supervisor or similar) in a related discipline who could comment on your work, this might be a suitable alternative. (See wsc's answer below.)

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As it was mentioned before, you can obtain reference letters from your supervisors, in case that you have done some internship job for obtaining your master´s. Also you can talk directly with one of your past professors, and explain them about your research interests (try to check first which professors have the same research interests). Then you can ask, in a nice way, if they can give you a hand with a recommendation letter. Most of the time they will agree to help you with that.

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