| Field | Communication |
| Went Obsolete | Varies |
| Made Obsolete By | Most often by the dominance of some other language |
| Knowledge Assumed | The language |
| When useful | Communicating. Expressing ideas common to a culture |
According to http://www.nytimes.com/2007/09/19/science/19language.html(approve sites) “Of the estimated 7,000 languages spoken in the world today, linguists say, nearly half are in danger of extinction and likely to disappear in this century. In fact, one falls out of use about every two weeks.”
A (small) list of extinct languages and more information at: http://en.wikipedia.org/wiki/Extinct_language
