A dead language is a language which is no longer learned as a native language. Some well known examples of dead languages include Coptic, Ancient Greek, Latin, and Sanskirt, although there are numerous other dead languages from regions around the world, including huge numbers of Native American languages which died out with European colonialism. Some dead languages are topics of study because of their cultural, linguistic, or social importance, and some dead languages actually have numbers of speakers which exceed those of modern or living languages, languages which are learned as native tongues.
In some cases, a dead language mutates into a modern language. Ancient Greek, for example, was the obvious precursor to Modern Greek, although the two languages are markedly different. Latin gave birth to Spanish, French, Italian, and Portuguese, while Sanskrit was the predecessor of many Indian languages. In these instances, many academics study the dead language to learn more about the history of a culture.
Studying dead languages can be very important if people want to learn about the history of the people who spoke them. Especially in instances where written languages were developed, knowing a dead language can open a window, by allowing people to read contemporary accounts of historical events. As you might imagine, many academics become embroiled in controversy over the specifics of a dead language, debating how things would have been pronounced, for example, or how specific words would have been used.
The term “dead language” is also used to refer to a language which is obviously on the way to death. In the Americas, for example, several Native American languages are known to a handful of older speakers, who may use them for communication, but these languages are obviously dying, as they are not used by the younger generation, and they have often stopped changing as well. In some communities, concerns about language death have led people to embark on programs which are designed to preserve these languages, and some communities have even tried to revive truly dead languages like Latin and Sanskrit.
The study of a culture's language can be very revealing, as the structure of a language can provide clues into how people look at the world and think about their relationships with other people, animals, and objects. This is why the study of dead languages is so interesting to so many people, and it explains why debate in the field can sometimes get heated, with various people supporting one view or another because it advances their personal opinions.