Every human group ever found has had language. No one has discovered a tribe, village or island without it, and today people speak roughly 7,000 languages. Linguistics is the scientific study of language: how it is built, how it is learned, how it changes and how it works in social life.

Speech, sign and writing

Language is not the same thing as speech. In the 1950s many people, including many teachers of deaf children, thought the signing of deaf people was a crude set of gestures. In 1960 the American scholar William Stokoe published a study showing that American Sign Language has its own structure, and later research confirmed it. Sign languages are full languages with their own grammar, not pantomime or codes for spoken words. American Sign Language is not English on the hands: it descends largely from French Sign Language, brought to the United States in 1817 by the deaf teacher Laurent Clerc, and it is quite different from British Sign Language.

Nor is language the same as writing, a recent invention that most languages in history never had. Level 8 returns to writing.

Describing, not prescribing

Many people think of "grammar" as school rules, such as never splitting an infinitive. Linguists use the word differently. Linguists describe how people actually speak rather than prescribing how they ought to. A grammar rule, in this sense, is a pattern that native speakers follow without ever being taught. No English teacher explains that we say "a big red ball" and never "a red big ball," yet every native speaker knows it. Style rules can be useful, but they are a different thing.

What makes language language

In 1960 the American linguist Charles Hockett proposed a list of "design features" that together set human language apart. A few matter most.

Arbitrariness means the link between a word's sound and its meaning is mostly a matter of convention. Nothing about the sound "dog" is doglike, which is why French says chien, German Hund and Spanish perro. Even words that imitate sounds differ: an English rooster says cock-a-doodle-doo, a German one kikeriki.

Displacement is the ability to talk about things that are not here and now: last winter, next year, a city across the ocean, a dragon that never existed.

Productivity means a limited stock of words and rules can produce an unlimited number of new sentences. You have probably never read this exact sentence before, yet you understood it.

Language is also passed on by learning, not by genes: a child raised in Seoul speaks Korean whatever her ancestry.

Animal communication

Studying animals sharpens the question. The Austrian scientist Karl von Frisch, who shared a Nobel Prize in 1973, decoded the honeybee's dance. The honeybee waggle dance tells hivemates the direction and distance of food. That is a form of displacement, since the food is far away. But a bee can discuss only a few topics, such as food and new nest sites, and it cannot say anything new.

Vervet monkeys in East Africa were studied by Robert Seyfarth, Dorothy Cheney and Peter Marler, who reported in 1980 that vervet monkeys give different alarm calls for leopards, eagles and snakes. When the researchers played recordings of the calls, monkeys ran up trees, looked up or looked down, as fitted each predator. The calls carry meaning, yet they form a small fixed set, and monkeys do not combine them into new messages. Simple call combinations found recently in some birds and apes are a subject of debate.

The most famous tests involved apes taught signs or symbols. The chimpanzee Washoe learned over a hundred signs in the 1960s and 1970s, and the bonobo Kanzi learned to use a keyboard of symbols and understood many spoken English requests. Supporters argue these apes showed real, if limited, linguistic ability. Critics point to Herbert Terrace, who led a project with a chimpanzee named Nim Chimpsky. After studying videotapes, Terrace concluded that Nim's signing was mostly imitation of his teachers, without grammar. Most linguists today hold that apes can learn symbols and some word meanings, but that no ape has shown the open-ended, structured productivity that every human child develops.

Worked example: one sentence, three species

Consider this sentence: "There was a leopard by the river yesterday, so let's take the long path tomorrow."

A vervet monkey has a call that means something like "leopard!" But the call warns of danger now. The monkey cannot say "yesterday," place the leopard by the river or propose a plan for tomorrow. The sentence uses displacement twice, into the past and the future, and vervet calls allow neither.

A honeybee does better on displacement. Its dance can point to a place far from the hive. But it can only point to food or a nest site. It cannot mention a predator, a time or a choice between routes.

A human speaker has no trouble. Each word is arbitrary: "leopard" sounds nothing like a leopard. The words fall into a structure that any English speaker understands at once, though they have probably never heard this sentence before. Bees and monkeys have systems well fitted to their lives. The comparison shows what is unusual about ours: it can carry any thought, about any time and place, in combinations no one has heard before.