In writing, just as in life, you’re selective when choosing words and the tone of voice you use in various situations. When writing a thank-you note to Great-Aunt Millie for the socks she sent you for your birthday, you probably use a polite, respectful voice. When you are having a fight with your partner or are gossiping with a friend, both your vocabulary and tone will be quite different. Likewise, you’ll use a more formal voice in a research paper compared to a personal essay, an email, or a journal entry.
Deciding what kind of voice to use in writing depends entirely on who will be reading what you write and what your purpose is in writing. Are you writing about the first time you ever drove a car? Explaining your theory about why yoga is such a popular exercise regimen and spiritual practice? Putting forth your informed opinion of why hybrid cars are problematic for the environment despite their increased gas mileage?
What creates voice is simply the words you choose and the way you use them. What kind of voice you use in a paper depends on the assignment and the audience, as well as the effect you want to create. By making conscious choices about the words you use to communicate to your reader, you establish a voice.