Types of individual languages
In the code table for ISO 639-3, the individual languages are identified as being of one of the following five types.
A language is listed as living when there are people still living who learned it as a first language.
This part of ISO 639 also includes identifiers for languages that are no longer living. A language is listed as extinct if it has gone extinct in recent times. (e.g. in the last few centuries). The criteria for identifying distinct languages in these case are based on intelligibility (as defined for individual languages).
A language is listed as ancient if it went extinct in ancient times (e.g. more than a millennium ago). In the case of ancient languages, a criterion based on intelligibility would be ideal, but in the final analysis, identifiers are assigned to ancient languages which have a distinct literature and are treated distinctly by the scholarly community. In order to qualify for inclusion in ISO 639-3, the language must have an attested literature or be well-documented as a language known to have been spoken by some particular community at some point in history; it may not be a reconstructed language inferred from historical-comparative analysis.
A language is listed as historic when it is considered to be distinct from any modern languages that are descended from it; for instance, Old English and Middle English. Here, too, the criterion is that the language have a literature that is treated distinctly by the scholarly community.
This part of ISO 639 also includes identifiers that denote constructed (or artificial) languages. In order to qualify for inclusion the language must have a literature and it must be designed for the purpose of human communication. Specifically excluded are reconstructed languages and computer programming languages.