Some definitions and basic facts important for historical linguistics

Donald Ringe, Spring 2012

Native language (back to top)
A native language is a language learned thoroughly in childhood, so that the speaker uses it perfectly without conscious control.

Critical period (back to top)
The critical period for native language acquisition (NLA) is the first few years of life. The grammar of a native language is normally acquired completely by the age of 7 or so; a native language cannot be acquired after puberty (so far as we know). Possibly for that reason, the basic grammar of a native language (phonemic structure, inflectional morphology, basic syntax) strongly resists modification later in life.

Linguistic descent (back to top)
Language or dialect Y of a given time is descended from language or dialect X of an earlier time if and only if X developed into Y by an unbroken sequence of instances of NLA. (Descent relationships are different in kind from other kinds of linguistic relationships, such as mutual influence through contact; be careful never to confuse them.)

Language family (back to top)
A language family is a group of languages descended from a single language of an earlier time. Members of a language family are said to be related to one another (whereas languages that have influenced one another by contact are not said to be related because of the contact). Members of a language family are often called daughters of the parent language (or ancestor) from which they are descended, or sister languages to each other.

Cognate (back to top)
Cognates are words and affixes in related languages that have been inherited from their common parent entirely by linguistic descent. Other linguistic items are not cognates, no matter now much they may resemble each other; in particular, words borrowed into a language are not cognates of the corresponding words in the language(s) they were borrowed from.

Sound change (back to top)
Spontaneous changes in pronunciation that occur in a language or dialect over extended periods of time (generations and centuries) are called sound changes. They apparently begin as native learner errors which survive into adulthood and spread through the speech community.

Regularity of sound change (back to top)
Within each line of linguistic descent, sound changes are overwhelmingly regular, such that either all instances of sound x in a given dialect in a given generation become sound x ́ over the course of the sound change, or, if there are conditions on which instances of x become x ́, they can be stated entirely in terms of other sounds in the same utterance (i.e., entirely in phonological terms). (Unfortunately other types of change occur too, and none of those other types is regular.)

Finally, a question to think about:
The definition of linguistic descent given above is just that, a definition; it doesn’t say how you can tell that Y is descended from X. Given that descent is a matter of an unbroken chain of NLA (not contact), and given what we know about what’s acquired in NLA, what sort of evidence would you look for if you wanted to demonstrate that a certain language Y is descended from another particular language X?