In language change, analogical change occurs when one linguistic sign is changed in either form or meaning to reflect another item in the language system on the basis of analogy or perceived similarity. In contrast to regular sound change, analogy is driven by idiosyncratic cognitive factors and applies irregularly across a language system. This leads to what is known as Sturtevant's paradox: sound change is regular, but produces irregularity; analogy is irregular, but produces regularity.
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".