The presence or absence of nasality can be designated as [+ nasal] or [- nasal}, with [m] being [+ nasal] and [b] or [p] being [- nasal]. A [- nasal] sound is equivalent to an oral sound.
The phonetic and phonemic symbols are cover symbols for a set or bundle of distinctive features, a shorthand method of specifying the phonetic properties of the segment. Phones and phonemes are not indissolube units; they are similar to molecules, composed of atoms phonetic features. A more explicit description of /p/, /b/, and /m/ may thus be given as :
Aspiration is not listed as a feature in the above phonemic specification of these units because it is non-distinctive and it is not necessary to include both [p] and [ ph] as phonemes. In a phonetic transcription, however, the aspiration would be specified where it occurs. This will be discussed later.
A phonetic feature is distinctive when the + value of that feature found in certain words contrast with the - value of that feature in other words. Each phoneme must be distinguished from all other phonemes in a language by at least one feature value distinction.
Since the phonemes /b/, /d/, and /g/ contrast by virtue of their place of articulation features labial, alveolar, and velar these place features are also distinctive in English. Since uvular sounds do not occurs in English, the place feature uvular is non-distinctive. The distinctive features of the voiced stops in English are shown in the following chart :
Each of the phonemes in the above chart differs form all the other phonemes by at least one distinctive feature.
The minimal pairs given in the following list illustrate some of the distinctive features in the phonological system of English.
The symbol [ _+] before a feature sould be read: 'plus minus' that feature, showing that it is a binary-valuated feature.
