Normal transmission

Normal transmission is the non-interrupted transmission of a language from one generation of speakers to the next one. In normal transmission the language is passed on to the child generation from the parent generation and/or the peer group, "with relatively small degrees of change over the short run"(Thomason & Kaufmann 1988: 9f.).

Example
A typical example of languages where there has been a break in transmission are creole languages and all other types of mixed languages.

Comments
Only if a language has undergone normal transmission can it be genealogically classified, which means there is one and only one direct parent of that language. To claim genealogical continuity of a language "entails systematic correspondences in all parts of the grammar because that is what results from normal transmission: what is transferred in normal transmission is an entire language---that is, a complex set of interrelated lexicon, phonological, morphosyntactic, and semantic structures."(Thomason & Kaufmann 1988: 11).

Reference

 * Thomason, Sarah Grey & Kaufmann, Terrence. 1988. Language Contact, Creolization, and Genetic Linguistics. Berkeley, Los Angeles: University of California Press.