Such grammars typically prescribe rules of correct or preferred usage. They divide words into form classes distinguished according to grammatical features. For example, a noun is defined in terms of its position in a sentence and its inflections, such as the -s for plural. The goal of this theory is to explain the uniformity of language acquisition among humans despite ostensible differences in their native languages. Since Chomsky's original proposals in 1957, numerous elaborations and alternative theories have been proposed.
Phonology involves analyzing how sounds function in a given language or dialect.
Phonologists examine such phonetic shifts to construct theories about linguistic sounds in one language that can be used in comparing linguistic systems. The analysis of sounds in different languages can be very useful for foreign language teachers. Morphology is the study of the structure of words. Morphologists study minimal units of meaning, called morphemes, and investigate the possible combinations of these units in a language to form words. The root, perfect , is transformed from an adjective into a noun by the addition of ion , made negative with im , and pluralized by s .