Language Variation and Change
A recent advertisement for Lockheed products claimed that if William the Conqueror had not had technological superiority when he invaded England in 1066, "this very ad might have been written in Anglo-Saxon". What's wrong with this picture? Two things: First, all living languages are always changing, so the Old English spoken by William's adversaries would be greatly different from Modern English even if there had been no Norman conquest. (Just try to read the 14th-century Middle English of Chaucer's Canterbury Tales without special training and you'll see how ordinary wear and tear can transform a language even when there are no dramatic military reversals to complicate things.) And second, although the aftereffects of William's adventure did bring a flood of French loanwords into English, English remained, and remains, a Germanic language: The bulk of the basic vocabulary and the bulk of the grammar are as Germanic as they ever were. The English population never did switch to French, the language of the conquerors; instead, the Norman French eventually switched to English.
Other Germanic languages include Dutch, German, Icelandic, Swedish, and more. All of them arose from a single language, called Proto-Germanic by linguists, which was spoken over 2500 years ago. Proto-Germanic was never written down, but its existence and much of its vocabulary and structure can be confidently inferred from the many systematic correspondences in words and grammatical structures shared by its descendants.
The break-up of Proto-Germanic happened when subgroups of the original speech community became separated: 500 to 1000 years of independent changes first produced divergent dialects, and then these became separate languages. The same thing happened to Latin after the Romans spread it over large parts of Europe; it split into dialects that turned into the modern Romance languages, among them French, Spanish, and Italian. Latin and Proto-Germanic were also related. Their ancestor, and the ancestor of many other languages of Europe, India, and points in between, was Proto-Indo-European, the parent of one of the world's most widespread language families.
There are dozens or even hundreds of other language families around the world, ranging from huge families like Niger-Congo in Africa and Indo-European to one-language families like Basque, which has no known linguistic relatives. Linguists still hope to connect many of these families, but the chances for reducing the number of separate language families to a handful are slim. Although most historical linguists believe that human language probably arose just once, in a single place at a particular time, most of them also believe that language change is too rapid and too sweeping to permit the verification of family relationships older than about ten thousand years. (This very rough estimate is based on the estimated time depths of well-established families and on the amounts of change over thousand-year periods.)
Everyone speaks at least one language, and probably most people in the world speak more than one. Even Americans, most of whom speak only English, usually know more than one dialect. Certainly no one talks exactly the same way at all times: You are unlikely to speak to your boss in the style (or vocabulary) that you'd use in talking to the idiot who just rammed your car from behind. All dialects start with the same system, and their partly independent histories leave different parts of the parent system intact. This gives rise to some of the most persistent myths about language, such as the claim that the people of Appalachia speak pure Elizabethan English. Non-Appalachians notice features of Shakespeare's English that have been preserved in Appalachia but lost in (for instance) Standard English, but only Appalachian fans of Shakespeare would be likely to notice the features of Shakespeare's English that have been preserved in Standard English but lost in the Appalachian dialect.
Types of Language Change
What kinds of language change are there? First, there's vocabulary change. Slang terms, in particular, come and go every few years. In a 1990 Beetle Bailey cartoon, for instance, Sarge chews Beetle out with a string of symbols ending in #!!, and Beetle laughs, "#?? Nobody says # anymore!" Sarge, deflated, sighs, "Gee, I always thought # was all-time classic cussing." Sarge is embarrassed because with a very few exceptions—notably the genuinely classic four-letter English words, at least one of which has a pedigree that includes a Latin obscenity written on the walls of ancient Pompeii—using last year's slang spells social disaster. Meanings of words change, too. English and German both inherited a word that refers to a person of high rank in English ('knight') but to a servant or even a slave in German ('Knecht'). (Thanks to evidence from other Germanic languages, we know that the German meaning is closer to the original.)
Grammatical constructions also change. A passage in the Old English Lord's Prayer reads, in literal translation, 'not lead thou us into temptation', in sharp contrast to Modern English 'don't lead us into temptation'. Nowadays, 'not' must follow an auxiliary verb 'do' (often contracted to 'don't'), there is no pronoun subject in the sentence, and if there were one it would be 'you'--'thou' has entirely disappeared from the modern language.
Last but not least, sounds change. Everyone realizes this, in a way, when dialect variation causes communication breakdown. If you go into a Chicago store and ask for 'sacks' in an East Coast accent you may get socks instead, and Bostonians sometimes have trouble understanding Alabamans even when both are using Standard English grammar. People are usually surprised, though, to discover that sound change is highly regular: if a sound 'x' changes to a sound 'y' in one word, 'x' will change to 'y' in comparable contexts in every word it appears in. As a result, the form of a word often reveals part of its history. Consider French 'coup' and English 'coup': They look alike, sound alike, and have similar meanings, but they can't both have been inherited independently from the same Proto-Indo-European (PIE) word, because the sound [k] doesn't come from the same PIE source in French and English. PIE (and, later, Latin) [k] did give rise to French [k], but original PIE [k] ended up as [h] in English. So there are pairs of words inherited from PIE in which French [k] corresponds to English [h], e.g. French 'coeur' and English 'heart', or French 'canevas' and English 'hemp'; but the reason the English words 'coup' and 'canvas' look like their French counterparts is that they were borrowed into English from French.
Change and Language Values
Language change inevitably leads to variation, and variation within a speech community often leads to social valuation of particular features as 'good' or 'bad'. 'Good' variants are typically believed to be characterized by logical superiority or venerability, or both; 'bad' variants must then be illogical and/or recent inventions by the vulgar.
But neither logic nor great age plays a significant role in the labeling of variants. Consider 'ain't', which may be the English word most despised by schoolteachers and pundits. Far from being illogical or recent, 'ain't' is a legitimate phonological descendant of 'amn't', which was the original contraction of 'am not'. It isn't clear how 'ain't' fell into disrepute, but once there, it left an awkward gap in the system of negative contractions: We have "You're going, aren't you?", "She's going, isn't she?", and so on, but surely no real person actually says "I'm going, am I not?". Instead, people say "I'm going, aren't I?", in part because they have been taught to avoid 'ain't' like the plague; and here logic shudders, because while "You are going, She is going," etc., are fine, "I are going" is impossible for native speakers of English. The point of this example is not to urge rehabilitation of ain't'—legislating language change is generally a losing proposition—but to illustrate the linguistically arbitrary nature of social valuation of the results of language change.
Trask, R. L. 1994. Language change. London and New York: Routledge.
Hock, Hans Henrich, and Brian D. Joseph. 1996. An introduction to historical and comparative linguistics. Berlin and New York: Mouton de Gruyter.
Romaine, Suzanne. 1994.Language in society: An introduction to sociolinguistics.Oxford: Oxford University Press.
Weinreich, Uriel. 1953. Languages in contact. The Hague: Mouton (repr. in 1968).