Students often ask how they can get their own opinion, position, and ideas in a formal paper without using 1st person. This typically leads to discussing voice (authorial in this case), tone, genre, perspective, and type (of writing).
Obviously, the perspective is partially a matter of authorial voice and tone. More of the latter, I think, in that while voice is important (if only to differentiate oneself from other writers), the formality or informality of the tone is often more important in various ways (I’ll mention this later). Which brings things back to “person” or perspective and its role in the type of writing.
It should be pretty clear that there is a difference between fiction and non-fiction writing and that the use of perspective/person in the two types is different as well. Purpose also comes into play, as does genre (by which I mean the kind of finished work—report, novel, scholarly essay, poem—rather than the marketing classification).
In non-fiction, first person is generally considered both informal and subjective. Since most forms of non-fiction attempt a degree of professionalism, formality and objectivity are desired. The exception here is first person plural, which can be used (sparingly) to connect with the audience. For example, saying “Based on this data, we see that . . .” places the writer amongst the audience as one of them. Second person, in non-fiction, is informally familiar or commanding. It also tends to backfire. For example, take the sentence, “The first thing you do in the morning is try not to step on the cat.” Quick show of hands: how many do not do this? And I’ve just sown the seeds of doubt in the minds of everyone whose hand is up, leading them to distrust everything else I say. Third person, though, is formal and is seen as being objective. Third person also projects confidence and certainty, even the presence or illusion of supporting data.
One other issue with first person in non-fiction is that writers, especially beginning writers, tend to slip into phrases like: “I believe,” “I feel,” “In my opinion,” etc. that sound uncertain, lack confidence, and generally serve to weaken the reader’s faith in the writer’s level of knowledge or expertise.
In fiction, we’re not concerned so much with authorial confidence, at least not in the same way. Nor are we worried about authorial objectivity. For fiction, perspective, I think, depends more on the author’s comfort level. Some people write better fiction using first person, others writer better with third. Both are effective and connect with readers, albeit in different ways. That said, first person can make the reader more emotionally connected and sympathetic (this can be true in non-fiction as well, and is fine in certain types of writing such as memoirs). First person tends to feel more like a conversation or being told a story in front of the fire. Second person fiction is, to the best of my knowledge, rare outside of dialogue or Choose Your Own Adventure books. It is very difficult to pull off in fiction.
I’ve found that one of the most difficult things to get early writers to understand is what we mean by “find your voice.” They tend to confuse “finding their voice” with writing like they speak, which is not true and only rarely works. Likewise, what works or is appropriate in one genre or rhetorical situation won’t necessarily work in another, e.g. one’s ability to effortlessly write good poetry has no bearing on the ability to write a good scholarly research paper or newspaper article and vice versa. This realization too, I think, is an important part of finding the writer’s authorial voice, and the evolution of that unique voice.