In its publications, the MLA generally does not use the plural pronoun they (or their, them, and themselves) to refer to singular nouns. While the singular they is not uncommon in spoken English and in some informal contexts, in formal writing it is best to reword for agreement in number. In the following example their and they are mismatched with each student:
Each student is expected to choose the topic of their research paper before they take the midterm.
In our editorial practice, our first preference is to cast the reference into the plural or to reword so that no pronoun is needed. In the first revision below, we have made the subject plural to agree with the pronouns. In the second, we have eliminated the pronouns.
Students are expected to choose the topic of their research paper before they take the midterm.
Each student is expected to choose a research paper topic before taking the midterm.
Alternatively, you may revise the pronouns to agree with a singular subject:
Each student is expected to choose the topic of his or her research paper before taking the midterm.
But constructions such as “his or her” are often cumbersome, and some writers may find singular, gender-specific constructions insufficient, given that many people do not identify with a particular gender. Using plural constructions, if possible, is often the best solution—and the most inclusive one—especially when you’re editing someone else’s writing.
Writers who wish to use a non-gender-specific pronoun to refer to themselves may prefer they and their (or a neologism like hir). Likewise, writers should follow the personal pronoun choices of individuals they write about, if their preferences are known, and editors should respect those preferences. They may be used in a singular sense according to a person’s stated preference for it:
They are writing their research paper on Austen’s Persuasion.
The MLA’s usage guidelines mostly follow the consensus of good practice among authors and editors of scholarly works. If a consensus emerges on a singular generic personal pronoun, we’ll most likely incorporate it into our usage.