In linguistics, a distinctive feature is the most basic unit of phonological structure that distinguishes one sound from another within a language. For example, the feature [+voice] distinguishes the two bilabial plosives: [p] and [b] (i.e., it makes the two plosives distinct from one another). There are many different ways of defining and arranging features into feature systems: some deal with only one language while others are developed to apply to all languages.
Distinctive features are grouped into categories according to the natural classes of segments they describe: major class features, laryngeal features, manner features, and place features. These feature categories in turn are further specified on the basis of the phonetic properties of the segments in question.
Since the inception of the phonological analysis of distinctive features in the 1950s, features traditionally have been specified by binary values to signify whether a segment is described by the feature; a positive value, [+], denotes the presence of a feature, while a negative value, [−], indicates its absence. In addition, a phoneme may be unmarked with respect to a feature. It is also possible for certain phonemes to have different features across languages. For example, could be classified as a continuant or not in a given language depending on how it patterns with other consonants. After the first distinctive feature theory was created by Russian linguist Roman Jakobson in 1941, it was assumed that the distinctive features are binary and this theory about distinctive features being binary was formally adopted in "Sound Pattern of English" by Noam Chomsky and Morris Halle in 1968. Jakobson saw the binary approach as the best way to make the phoneme inventory shorter and the phonological oppositions are naturally binary.
In recent developments to the theory of distinctive features, phonologists have proposed the existence of single-valued features. These features, called univalent or privative features, can only describe the classes of segments that are said to possess those features, and not the classes that are without them.
List
thumb|[[Euler diagram showing a typical classification of sounds (in IPA) and their manners of articulation and distinctive features|class=skin-invert-image]]
This section lists and describes distinctive features in linguistics.
Major class
Major class features: The features that represent the major classes of sounds.
- [+/− syllabic] Syllabic segments may function as the nucleus of a syllable, while their counterparts, the [−syll] segments, may not. Except in the case of syllabic consonants, [+syllabic] designates all vowels, while [−syllabic] designates all consonants (including glides).
- [+/− consonantal] Consonantal segments are produced with an audible constriction in the vocal tract, such as obstruents, nasals, liquids, and trills. Vowels, glides and laryngeal segments are not consonantal.
- [+/− approximant] Approximant segments include vowels, glides, and liquids while excluding nasals and obstruents.
- [+/− sonorant]
- [+/− diffuse] backward-flanged: labial and coronal, narrow vowel (low vowels) Distinctive features have also been used to distinguish proverbs from other types of language such as slogans, clichés, and aphorisms.
Analogous feature systems are also used throughout Natural Language Processing (NLP). For example, part-of-speech tagging divides words into categories. These include "major" categories such as Noun vs. Verb, but also other dimensions such as person and number, plurality, tense, and others. Some mnemonics for part-of-speech tags conjoin multiple features, such as "NN" for singular noun, vs. "NNS" for plural noun, vs. "NNS$" for plural possessive noun (see Brown Corpus). Others provide more explicit separation of features, even formalizing them via markup such as the Text Encoding Initiative's feature structures. Modern statistical NLP uses vectors of very many features, although many of those features are not formally "distinctive" in the sense described here.
See also
- Feature geometry