Pure vowels

How are pure vowels characterized in English?
A brief description.

Before learning about their features, we have to get to know to them.

*/i:/ the fleece

/ɪ/ the kit

/e/ the dress

/æ/ the trap

/ɜ:/ the nurse

/ə/ the shwa

/ʌ/ the strut

/ɑ:/ the palm

/ɒ/ the lot

/ɔ:/ the thought

/ʊ/ the foot

/u:/ the goose

* Key words devised by Professor J.C. Wells and widely used as a standard set.

Phonetically.

Vowels are produced by a stricture of open approximation. This means that The air goes out unimpeded centrally over the tongue without contact of the articulators. Because of this, they are no easy to describe in terms of articulation and they are learned auditorily by listening and imitation.
In all cases we assume that the soft palate is raised, the vocal cords vibrating and the tongue tip behind the lower teeth.
To know in what ways vowels differ from each other, we have to consider the shape and position of the tongue and the shape of the lips.

Let's see below their phonetics features:

Part of the tongue

This trapezium represents the position of the tongue in the mouth.

/i:, ɪ, e, æ/ are produced with an approximation of the blade of the tongue towards the alveolar ridge, in the production of /ɜ:, ə, ʌ/ the approximation is made by the front of the tongue towards the hard palate and finally we approximate the back of the tongue with the soft palate in order to produce /ɑ:, ɒ, ɔ:, ʊ, u:/.

We can also observe that the tongue can be raised to different levels, this is what its called height of the tongue (vertical distance between the upper surface of the tongue and the palate) close, half-closed, half-open, open.
According to its height /i:/ and /u:/ are produced with the tongue near a closed position, /ɪ/ and /ʊ/ above the half-closed position, /ɜ:, ə/ and /ɔ:/ below the half-closed, /e/ in a medial position, /ɒ/ below the half-open position, /ʌ/ between the half-open and open position and /æ/ and /ɑ:/ above the open position (though /æ/ is produced higher than /ɑ:/ ).

Shape of the lips:

Pure vowels are also made different from each other bymodifying the shape of the lips: spread, rounded and neutral. This gives each sound its particular quality.

Length and tenseness
By tensing or laxing the muscles, which affects the length of the sound, we can produce 5 long (tense) vowels /i:, ɜ:, ɑ:, ɔ:, u:/ or 7 short (lax) vowels /ɪ, e, æ, ə, ʌ , ɒ, ʊ/. The tenser the muscles are, the longer the vowels are. This gives each pure vowel sound its quantity.

Phonologically.
In English they function as the nucleus of the syllable in words, this means that they make up the prominent parts of the syllables. This is the reason why they are vocalic elements.

Distribution

When it has to do with their distribution, we have to consider that:

-All the long vowels occur in all positions and the short vowels /e, æ, ʌ, ɒ, ʊ/ have restricted occurrence to initial and medial position.
-The schwa (/ə/) has restricted occurrence to unstressed syllables.

Let's see distribution vowel by vowel:

/i:/
initial position: east /i:st/
medial position: keep /ki:p/
final position: knee /ni:/

/ɪ/
initial position: image /ɪmɪdʒ/
medial position: kit /kɪt/
final position: city /sɪtɪ/

/e/
initial position: egg /eɡ/
medial position: head /hed/

/æ/
initial position: apple /æpl/
medial position: path /pæθ/

/ɜ:/
initial position: earth /ɜ:θ/
medial position: perfect /pɜ:fekt/
final position: fur /fɜ:/

/ə/
initial position: away /əweɪ/
medial position: family /fæməlɪ /
final position: mirror /mirə/

/ʌ/
initial position: unusual /ʌnju:ʒʊəl/
medial position: tounge /tʌŋ/

/ɑ:/
initial position: arm /ɑ:m/
medial position: hard /hɑ:d/
final position: kar /kɑ:/

/ɒ/
initial position: office /ɒfis/
medial position: dog /dɒɡ/

/ɔ:/
initial position: also /ɔ:lsəʊ/
medial position: broght /brɔ:t/
final position: straw /strɔ:/

/ʊ/
initial position: umlaunt /ʊmlaʊt/
medial position: pull /pʊl/

/u:/
initial position: ooze /u:z/
medial position: use /ju:s/
final position: zoo /zu:/

Allophonic variants

Pre-fortis clipping
Pre-fortis clipping is a phonological process in which pure vowels can be clipped or shortened before voiceless or fortis consonants and can be lengthened before voiced or lenis consonants within the same syllable and in final position. All pure vowels, except for the schwa, undergo this process. This process does not only apply for pure vowel but also it applies for diphthongs.

In narrow transcription, the length of the vowel is represented by means of a dot [ˑ]:

-In the case of long vowels, that are represented by 2 dots, this single dot [ˑ] is used when the vowel is shortened because it is followed by a fortis consonant.
-When long vowels are followed by voiced consonants or when they are found in final position, the length does not change and so we must keep the 2 dots

keep [kiˑp] need[ni:d] knee [ni:]

birth [bɜˑθ] hers [hɜ:z] fur [fɜ:]

cart [kɑˑt] hard [hɑ:d] car [kɑ:]

force [fɔˑs] all [ɔ:l] law [lɔ:]

suit [suˑt] ooz [u:z] two [tu:]

-On the other hand, in the case of short vowels, the dot [ˑ] is used when the vowel is lengthened because it is followed by a voiced consonant. In the case of /ɪ/,It is neutralized in final position with /i:/ and turns into /i/.
-When they are followed by fortis consonants, the length does not change and so we don't have to add any dot.