Most of us would agree that the people in Brooklyn and the people on the Mississippi Delta speak dialects of the English language-well, of the US dialect of the English language. However, if someone who has seldom left Brooklyn were to meet an African American who has seldom left his rural home in the Mississippi Delta, they would hardly be able to communicate with each other. You can imagine the problems between a life-long resident of Yorkshire, England and a Mississippian from the Delta.
In the movie, "My Cousin Vinny," there is a famous scene in which the Brooklyn character played by Joe Pesci refers to "the two yutes [youths] in question" and the educated Southern judge, played by Fred Gwynne, has no idea what he is referring to. This breakdown of communications, however, would have been much more profound had Joe tried to talk to rural African Americans.
So where do dialects come from and how do they become languages? First, how do dialects arise? As the population speaking a language increases, it tends to expand, to migrate away from the center. The farther away from the center it moves, the more difficult it is to keep up with the constant changes taking place in the central area.
Moreover, migration takes people into areas where other languages are spoken. In interacting with members of the other linguistic culture, features of the other language little by little creep into the migrating language. These changes do not match those that are taking place at the center and, over the years, they mount up until the migrating population is speaking with a distinct accent-like people from Brooklyn and Long Island.
The migratory population moves farther and farther away, integrating more and more with the foreign culture. The differences between its accent and that of the central population increase until they are speaking a distinct dialect of the language. Now we have strongly noticeable differences, such as the speech of Mississippians and Brooklynites.
Even if the central population has massive TV, radio, and motion picture facilities, if the two populations do not talk with each other on a regular basis, the dialects become more and more dissimilar and comprehension becomes more and more difficult.
This brings us to the second question: at what point does a dialect become an independent language? When the two dialects are 51% mutually incomprehensible? When they are 66.67% mutually incomprehensible? When they are 82.4567% mutually incomprehensible? As you can see, it is impossible to draw a line without arbitrarily defining what dialects and languages are.
This problem has led to some interesting inconsistencies in the use of the terms "dialect" and "language." Norwegian, Swedish, and Danish are essentially striking dialects of the same language.
On the other hand, what we refer to as "Chinese" is, in fact, at least 7 different languages: Mandarin, Cantonese, Hakka, Xiang, Min, Gan, and Wu. These languages are usually referred to as "dialect groups" which amounts to the same thing as languages—right? Speakers of these languages cannot communicate with each other at all or only to a very limited degree.
How did this situation come to pass? Someone once said that a language is a dialect with an army. If the Norwegians, Swedes, and Danes have distinguishable borders that they can defend, that is more important than distinguishable, mutually incomprehensible languages.
It should therefore come as no surprise, then, that speakers of Serbo-Croatian in the former Yugoslavia, now claim to speak distinct languages: Croatian, Serbian, and Bosnian. Each of their territories have been recognized as sovereign states (and all are building up their armies). Yet the differences between these languages, as spoken in their capitals, are less than those distinguishing Brooklyn and Mississippian US English.
If you spoke Croatian in the northernmost province of Croatia, then slowly traveled south, say, 50 miles or so, then stopping for a week to learn the slight differences in the local dialect each time you stopped, by the time you reached Sophia, you would be speaking Bulgarian. No where from Zagreb, Croatia to Sofia, Bulgaria is there a clear line between languages though speakers from Zagreb, Croatia can barely understand anyone speaking Bulgarian.
It is difficult to count all the conflicts that have arisen from drawing geopolitical boundaries without consideration of linguistic and cultural ones. About a third of the Kurds live in Iraq, another third in Turkey, and another third in Afghanistan. All live with the dream of one day living in their own Kurdistan-they even have a flag and coat of arms. However, until they have an army, they lack the means of achieving their dream.