Children can learn any language they are exposed to. Take a moment to consider how remarkable that ability is. If you put any infant born without developmental disabilities in any culture, that child will learn the language—or languages—he or she hears spoken. Ethnic origin makes no difference to this fluency. A child of Japanese parents raised by English speakers will grow up speaking fluent English. A child of European ancestry will learn to speak perfect Navajo if raised among Navajo speakers. And no special training is necessary. By the time children reach school age, they have already mastered the basic structures and vocabulary of their native language, even if their parents give them no special instruction.

Adults, by contrast, lack this ability. Although a lucky few can absorb new languages easily, most people require laborious study to learn a new language after childhood. Many immigrants, for example, live in their new country for years and never completely master the local language, even after making sustained efforts to study it. Pronunciation in particular can be a continuing source of difficulty, even when the speaker is otherwise fluent. Henry Kissinger, a professor and former Secretary of State whose written English is sophisticated and complex, betrays his German origins every time he speaks. And he immigrated to the United States at the age of 15.

This contrast between children and adults suggests that there is something biological to language, that it is not just an arbitrary invention of human cultures. Children seem biologically primed to acquire a language as part of their development and lose this ability as they mature. What is this biological basis of language? Are there basic similarities among languages that make it easier for children to master them, or do languages vary without limit? What are the rules of a language, and how do people learn those rules? These are a few of the basic questions that the subject of linguistics tries to answer.

Linguistics is the study of the basic nature and structure of human language. It tries to explain the fundamentals of how language works. That focus means that linguistics attends to different aspects of language than do the other language arts with which you may be more familiar. For example, one reason people study languages is to learn how to communicate with other speakers of that language, as in the classes in Spanish, French, or other languages that most high-school students take. Linguists, of course, do need to study languages, but communication with others isn't typically their primary goal. A linguist trying to explain some basic feature of language may examine hundreds of languages from all over the world—relying on descriptions of these languages by specialists—without being able to communicate in more than a handful of them.

Linguistics also distinguishes itself from the other language arts by its scientific approach. Like other sciences, linguistics constructs theories and tests the validity of these theories against empirical evidence. Linguists for the most part study how people actually use language, whether or not that use matches what schoolbooks claim is the "correct" form of the language. Linguistics wants to explain things the way they actually are, not to change them according to some preconceived notion. Consider, for example, an utterance such as

(1) Me and Sally ain't never been friends.

Grammar books like those you probably used in high school would dismiss this sentence as ungrammatical, telling you that ain't is not a word, that me mustn't be used in the subject of a sentence, and that you can't use two negatives together. Yet people utter this sort of sentence every day despite repeated and strenuous objections from teachers. An adequate description of English must explain this fact.