Explanation I use in comments on student papers:
Both the personal and public voice (“I believe,” “we believe”) are viable when conducting a critical argument. However, there can be a problem if a paper begins in one voice and suddenly switches to the other, or if it randomly goes back and forth between the two.
There are two solutions to this problem: either be consistent in voice; or oscillate between “we” and “I” as needed. By oscillation, I do not mean a random alternation but splitting the tasks of the paper between the two voices. Often, good writers will use the “we” voice when they speak about broadly held views or when they are trying to reach out to include the reader; then they will switch to the “I” voice to break with convention and advance a novel or contrasting view–a kind of good cop, bad cop routine. For example, “We commonly think that a poem should seduce us with its beauty. But I would advance the thesis that hard work is needed first.”
