Reviewer of PhD thesis doesn't allow me to write in the first person singular In my PhD thesis, I often used the first person singular during the description of the problem and the discussion of the results. One comment from the reviewer states that because I did not use the third person, the entire thesis must be revised accordingly.

I understand that in a journal article one should use the third person to describe the problem and discuss the findings. However, I always supposed that one can use the first person in a PhD thesis because I saw many researchers doing so. Could anybody give me a suggestion about how to deal with the reviewer who doesn't accept my choice to write in the first person?
There is an annoying truth here: What's OK in a PhD thesis and what not largely depends on the reviewers. Some people in academia have a huge inflated ego and prefer things to be done as they suggest, and the reviewer in your case is possibly among those people. You don't want to fight with them on this kind of issue.

If the reviewer has other comments that tend to create additional work without clearly improving the thesis, you may consider exchanging the reviewer.