Each year, the American Dialect Society selects a “Word of the Year.” Recent winners include tweet, a “short, timely message sent via the Twitter.com service,” and app, “an abbreviated form of application, a software program for a computer or phone operating system.” Even the Oxford English Dictionary—the resource that defines the English language—annually announces what new terms have officially been added to the English vocabulary.

Many people view language as fixed. But in fact, language constantly changes. A particular language’s constitutive rules—which define the meanings of words—may shift. As time passes and technology changes, people add new words to their language and discard old ones. Sometimes people create new phrases, such as helicopter parent, that eventually see wide use. Other times, speakers of a language borrow words and phrases from other languages and incorporate them into their own.

A language’s regulative rules also change. When you learned to speak and write English, for example, you probably were taught that they is inappropriate as a singular pronoun. But before the 1850s, people commonly used they as the singular pronoun for individuals whose gender was unknown—for example, “the owner went out to the stables, where they fed the horses” (Spender, 1990). In 1850, male grammarians petitioned the British Parliament to pass a law declaring that all gender-indeterminate references be labeled he instead of they (Spender, 1990). Since that time, teachers of English worldwide have taught their students that they used as a singular pronoun is “not proper.”