Stop consonant

A stop, plosive, or occlusive is a consonant sound produced by stopping the airflow in the vocal tract. The term plosive is reserved for oral (non-nasal) stops: that is, stops with a release burst.

All languages in the world have stops. Most have at least [p], [t], [k], [n], [m]. However, colloquial Samoan lacks the dentals [t] and [n], and the northern Iroquoian languages lack the labials [p] and [m]. Several of the Chimakuan, Salishan, and Wakashan languages around Puget Sound lack nasal stops.

Stop articulation
In the articulation of the stop, three phases can be distinguished:
 * Catch: The airway closes so that no air can escape through the mouth (hence the names stop). With nasal stops, the air escapes through the nose.
 * Hold or occlusion: The airway stays closed, causing a pressure difference to build up (hence the name occlusive).
 * Release or burst: The closure is opened. In the case of plosives, the released airflow produces a sudden impulse causing an audible sound (hence the name plosive).

In many languages, such as Malay and Vietnamese, final stops lack a release burst, or have a nasal release. See Unreleased stop.

In affricate stops, the release is a fricative.

Nasalization
nasal stops are differentiated from oral stops only by a lowered velum that allows the air to escape through the nose during the occlusion.

Nasal stops are acoustically sonorants, as they have a non-turbulent airflow and are nearly always voiced, but they are articulatorily obstruents, as there is complete blockage of the oral cavity.

A prenasalized stop starts out with a lowered velum that raises during the occlusion. The closest examples in English are consonant clusters such as the [nd] in candy, but many languages have prenasalized stops that behave as single consonants. Swahili is well known for having words that begin with sounds like [mp] or [nd].

A postnasalized stop begins with a raised velum that lowers during the occlusion. This causes an audible nasal release, as in English sudden. Russian and other Slavic languages have words that begin with [dn], which can be seen in the name of the Dnieper River.

Note that the terms prenasalization and postnasalization are normally only used in languages where these sounds are phonemic, that is, not analyzed into sequences of plosive plus nasal stop.

Voice
Voiced stops are articulated with simulaneous vibration of the vocal cords, voiceless stops without. Plosives are commonly voiceless, whereas nasal stops are only rarely so.

Aspiration
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 duration between the release of the stop and the voice onset is called voice onset time (VOT). Tenuis stops have a voice onset time close to zero, meaning that voicing begins when the stop is released. Voiced stops have a negative voice onset time, meaning the voicing begins before the stop is released. A stop is called "fully voiced" if it is voiced during the entire occlusion. In English, however, initial voiced plosives like [b] or [d] are only partially voiced, meaning that voicing picks up sometime during the occlusion. Aspirated stops have a voice onset time greater than zero, so that there is a period of voiceless airflow (a phonetic voiceless glottal fricative) before the onset of the vowel.

In most dialects of English, the final g in the word bag is likely to be fully voiced, while the initial b will be only partially voiced. Initial voiceless plosives, like the p in pie, are aspirated, with a palpable puff of air upon release, while a plosive after an s, as in spy, is tenuis. If you speak near a candle flame, you will see that the flame will flicker more when you say pie, tie, chi than when you say spy, sty, sky.

Length
In a geminate or long stop, the occlusion lasts longer than in normal stops. In languages where stops are only distinguished by length (e.g. Arabic, Ilwana, Icelandic), the long stops may last up to three times as long as the short stops. Italian is well known for its geminate stop, as the double t in the name Vittoria takes just as long to say as the ct does in English Victoria.

Note that there are many languages where the features voice, aspiration, and length reinforce each other, and in such cases it may be hard to tell which of these features predominates. In such cases the terms fortis is sometimed used for aspiration or gemination, while lenis is used for single, tenuis or voiced stops. Beware, however, that the terms fortis and lenis are poorly defined, and their meanings vary from source to source.

Airstream mechanism
Stops may be made with more than one airstream mechanism. The normal mechanism is pulmonic egressive, that is, with air flowing outward from the lungs. All languages have pulmonic stops. Some languages have stops made with other mechanisms as well: ejective stops (glottalic egressive), implosive stops (glottalic ingressive), or click consonants (velaric ingressive).

Tenseness
A fortis stop (in the narrow sense) is produced with more muscular tension than a lenis stop (in the narrow sense). However, this is difficult to measure, and there is usually debate over the actual mechanism of alleged fortis or lenis consonants.

There are a series of stops in Korean, sometimes written with the IPA symbol for ejectives, which are produced using "stiff voice", meaning there is increased contraction of the glottis than for normal production of voiceless stops. The indirect evidence for stiff voice is in the following vowels, which have a higher fundamental frequency than those following other stops. The higher frequency is explained as a result of the glottis being tense. Other such phonation types include breathy voice, or murmur; slack voice; and creaky voice.

Examples
Here are the oral stops (plosives) granted dedicated symbols in the IPA. See also the nasal stops.


 * voiceless bilabial plosive
 * voiced bilabial plosive
 * voiceless alveolar plosive
 * voiced alveolar plosive
 * voiceless retroflex plosive
 * voiced retroflex plosive
 * voiceless palatal plosive
 * voiced palatal plosive
 * voiceless velar plosive
 * voiced velar plosive
 * voiceless uvular plosive
 * voiced uvular plosive
 * epiglottal plosive
 * glottal stop

English stops
,, (aspirated word-initially, tenuis in clusters with s)

,, (in most dialects: partially voiced word-initially, fully voiced intervocalically)

,, (fully voiced nasal stops)

(glottal stop, not as a phoneme in most dialects)