Uniformitarian principle (linguistics) in the context of "Historical linguist"

Language change is the process of alteration in the features of a single language, or of languages in general, over time. It is studied in several subfields of linguistics: historical linguistics, sociolinguistics, and evolutionary linguistics. Traditional theories of historical linguistics identify three main types of change: systematic change in the pronunciation of phonemes, or sound change; borrowing, in which new features (often, new words) enter a language or dialect as a result of influence from another language or dialect; and analogical change, in which the shape or grammatical behavior of a word is altered to more closely resemble that of another word. Research on language change generally assumes the uniformitarian principle—the presumption that language changes in the past took place according to the same general principles as language changes visible in the present.

Language change usually does not occur suddenly, but rather takes place via an extended period of variation, during which new and old linguistic features coexist. All living languages are continually undergoing change. Some commentators use derogatory labels such as "corruption" to suggest that language change constitutes a degradation in the quality of a language, especially when the change originates from human error or is a prescriptively discouraged usage. Modern linguistics rejects this concept, since from a scientific point of view such innovations cannot be judged in terms of good or bad. John Lyons notes that "any standard of evaluation applied to language-change must be based upon a recognition of the various functions a language 'is called upon' to fulfil in the society which uses it".

Historical linguistics, also known as diachronic linguistics, is the scientific study of how languages change over time. It seeks to understand the nature and causes of linguistic change and to trace the evolution of languages. Historical linguistics involves several key areas of study, including the reconstruction of ancestral languages, the classification of languages into families, (comparative linguistics) and the analysis of the cultural and social influences on language development.

This field is grounded in the uniformitarian principle, which posits that the processes of language change observed today were also at work in the past, unless there is clear evidence to suggest otherwise. Historical linguists aim to describe and explain changes in individual languages, explore the history of speech communities, and study the origins and meanings of words (etymology).