In theoretical linguistics

Theoretical linguistics

Theoretical linguistics is the branch of linguistics that is most concerned with developing models of linguistic knowledge. The fields that are generally considered the core of theoretical linguistics are syntax, phonology, morphology, and semantics...

, underspecification is a phenomenon in which certain feature

Feature (linguistics)

A feature is a concept applied to several fields of linguistics, typically involving the assignment of binary or unary conditions which act as constraints.-In phonology:...

s are omitted in underlying representation

Underlying representation

In some models of phonology as well as morphophonology, the underlying representation or underlying form of a word or morpheme is the abstract form the word or morpheme is postulated to have before any phonological rules have applied to it. If more rules apply to the same form, they can apply...

s. Restricted underspecification theory holds that features should only be underspecified if their values are predictable. For example, in English

English language

English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

, all front vowel

Front vowel

A front vowel is a type of vowel sound used in some spoken languages. The defining characteristic of a front vowel is that the tongue is positioned as far in front as possible in the mouth without creating a constriction that would be classified as a consonant. Front vowels are sometimes also...

s (/i, ɪ, e, ɛ, æ/) are unrounded

Roundedness

In phonetics, vowel roundedness refers to the amount of rounding in the lips during the articulation of a vowel. That is, it is vocalic labialization. When pronouncing a rounded vowel, the lips form a circular opening, while unrounded vowels are pronounced with the lips relaxed...

. It is not necessary for these phoneme

Phoneme

In a language or dialect, a phoneme is the smallest segmental unit of sound employed to form meaningful contrasts between utterances....

s to include the distinctive feature

Distinctive feature

In linguistics, a distinctive feature is the most basic unit of phonological structure that may be analyzed in phonological theory.Distinctive features are grouped into categories according to the natural classes of segments they describe: major class features, laryngeal features, manner features,...

[−round], because all [−back] vowels are [−round] vowels, so the distinctive feature is not distinctive if we know the vowel to be front. Radical Underspecification theory, on the other hand, also allows for traditionally binary features to be specified for only one value, where it is assumed that every segment not specified for that value has the other value. For example, instead of the features [+voice] and [−voice], only [+voice] is specified and voicelessness is taken as the default.