A stop or plosive or occlusive is a consonant sound produced by stopping the airflow in the vocal tract.
All languages in the world have stops (some Polynesian languages have only three). Most languages have at least [p], [t], [k], [n], [m] (though the latter two aren't considered stops by all).
In the articulation of the stop, three phases can be distinguished:
- Catch or implosion: The airway closes so that no air can escape through the mouth (hence the names stop). If the nasals are considered stops, then the air might still escape through the nose.
- Hold or occlusion: The airway stays closed causing a pressure difference to build up (hence the name occlusive).
- Release or explosion: The closure is suddenly opened; the released airflow produces a sudden impulse causing an audible sound (hence the name plosive).
In certain languages, final stops may lack the release. In affricate stops, the release simultaneously is a fricative.
Classification of stops
Some linguists consider nasal consonants to be nasal stops, which are differentiated from the oral stop only by the lowered velum that allows the air to escape through the nose during the production of the nasal stop.
Other linguists consider the nasal consonants not to be stops because they are continuants and call them simply nasals, as opposed to stops.
A prenasalized (oral) stop begins with a lowered velum that raises during the second phase of the stop articulation (e.g. [nd] in the English word candy which is phonetically a prenasalized stop).
A postnasalized (oral) stop begins with a raised velum that lowers during the second phase of the stop articulation. This lowering of the velum causes an audible nasal release (e.g. [dn] in the English words Edna, sudden which is phonetically a postnasalized stop).
Note that the terms prenasalization and postnasalization are normally only used in languages where these sounds are not analyzed into sequences (clusters) of (oral) stop and nasal (stop).
Voiced stops are articulated with simulaneous vibration of the vocal cords, voiceless stops without.
In aspirated stops, the voice onset (the time when the vocal cords begin to vibrate) comes perceivably later than the release of the stop. The deviation between the release of the stop and the voice onset is called voice onset time (VOT).
In a long stop, the hold takes more time. In languages where stops are only distinguished by length, the long stops take about three times longer than the short stops. Long stops are often called geminates.
Note that there are many languages where the features voice, aspiration, and length depend on each other (e.g. in English). Because it may be hard to tell which one of these features is predominant, the terms fortis and lenis are sometimes used (in their broader sense).
Stops may be made with more than one airstream mechanism. The normal mechanism is pulmonic, that is with air flowing outward from the lungs. All languages have pulmonic stops. Some languages have stops made with other mechanisms too: these are called ejective, implosive, or click dependent on the mechanism.
A fortis stop (in the narrow sense) is produced with more muscular tension than a lenis stop (in the narrow sense). This feature has never been proved in measurements.
Here are some of the oral stops. (The figures in square brackets are from the IPA.)
[p], [t], [k] (voiceless)
[b], [d], [g] (voiced)
[m], [n], [ŋ] (nasal, and not considered stops by all)
[ʔ] (glottal stop, though not as a phoneme in most dialects)