Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Choose an appropriate level of formality
Choose appropriate language
Clarity

Language is appropriate when it suits your subject, engages your audience, and blends naturally with your voice.

To some extent, your choice of language will be governed by the conventions of the genre in which you are writing. When in doubt about the conventions of a particular genre — lab reports, informal essays, business memos, and so on — consult your instructor or look at models written by experts in the field.

17a Choose an appropriate level of formality.

In deciding on a level of formality, consider both your subject and your audience. For most college and professional writing, some degree of formality is appropriate. In a job application, for example, it is a mistake to sound too breezy and informal.

In choosing a level of formality, above all be consistent. When a writer’s voice shifts from one level of formality to another, readers receive mixed messages.