It is a reference point which is fixed and unchanged, established within the total range of vowel quality to which any other vowel sound can be directly related.

That means we can establish certain points which are accepted as fixed and unchanged. This system of reference points is called a system of cardinal vowels. The exact value of quality of any vowel may be defined within the system. The idea of the system was defined yet in the 18-th century, and the number of cardinal vowels varied. In England it was introduced by D. Jones. The principal cardinal vowels are 8 in number.

All the English vowels are classified according to the system of cardinal vowels. Any vowel may be defined in reference to it.

2. Classification of English vowels.

Vowels are made by voiced air passing through different mouth-shapes; the difference in the shape of the mouth are caused by different positions of the tongue and of the lips

There are 21 vowel phonemes in English. They are divided first of all into two large groups: monophthongs and diphthongs. This division is based on the stability of articulation.

A monophthong is a vowel in the pronunciation of which the organs of speech (principally the tongue and the lips) do not change their position throughout the duration of the vowel.

The particular quality, or timber of vowels depends on the volume and shape of the mouth-resonator and to a great extent also on the shape and the size of the opening of the resonator.

However, in English the character of certain vowels varies not only with their quality, but also with their quantity, or length (duration).

Thus the English monophthongs may be classified according to the following principles:

the position of the tongue;

the position of the lips;

their length;

the degree of tenseness;

The first two principles are the main ones because they reflect the qualitative characteristic of the English vowel phonemes, which is their most important feature, while their quantitative characteristic is of secondary importance. This is because the length of one and the same English vowel phoneme noticeably changes in different positions, while its quality remains unchanged. For example, the English [i:] in the word [si:t] seat is shorter than in the word [si:d] seed, although the quality of the vowel sound in both words is the same.

1. Classification of the vowels according to the position of the tongue.

1. According to the position of the bulk of the tongue (or the horizontal movement of the tongue) vowels are divided into five groups: (A) front, (B) front-retracted, (C) mixed, (D) back and (E) back-advanced.

(A) Front vowels are those in the production of which the bulk of the tongue is in the front part of the mouth while the middle part of the tongue is raised in the direction of the hard palate.

(B) Front-retracted vowels are those in the production of which the bulk of the tongue is in the front part of the mouth, but somewhat retracted, while the middle part of the tongue is raised in the direction of the hard palate.

(C) Mixed vowels are those in the production of which the tongue is neither advanced nor retracted, and both the middle and the back of the tongue are raised in such a way that the surface of the tongue is more or less flat.

(D) Back vowels are those in the production of which the bulk of the tongue is in the back part of the mouth while the back part of the tongue is raised in the direction of the soft palate.

(E) Back-advanced vowels are those in the production of which the bulk of the tongue is in the back of the mouth, but somewhat advanced , while the back part of the tongue is raised in the direction of the front part of the soft palate, forming an empty space in the front part of the mouth.

2. According to the height of the raised part of the tongue (or the vertical movement of the tongue) vowels are divided into three groups: (A) close, or high vowels, (B) open, or low vowels and (C) mid-open, or mid, vowels.

(A) Close (high) vowels, or vowels of a high position of the tongue, are those in the production of which one of the parts of the tongue comes close to the roof of the mouth and the air-passage is narrowed, but not so much as to form a consonant.

(B) Open (low) vowels, or vowels of a low position of the tongue, are those in the production of which the tongue is very low in the mouth, and the air-passage is very wide.

(C) Mid-open (mid) vowels, or vowels of a medium position of the tongue are those in the production of which the highest part of the tongue

is half-way between its high and low positions, described above.

Each of these three main tongue-positions (high, mid and low) has two variations: narrow and broad. This means that in pronunciation a vowel of a narrow variation of each of the three main tongue-positions the part of the tongue involved is raised a little higher than the same part in pronouncing a vowel of a broad variation of the same general tongue-position. This makes it convenient to subdivide each of the three above-mentioned large groups of English vowels into the following smaller groups:

Close vowels into:

(a) vowels pronounced with a narrow variation of a high position of the tongue;

(b) vowels pronounced with a broad variation of a high position of the tongue.

Open vowels into:

(a) vowels pronounced with a narrow variation of a low position of the tongue,

(b) vowels pronounced with a broad variation of a low position of the tongue.

Mid-open vowels into;

(a) vowels pronounced with a narrow variation of a medium position of the tongue,

(b) vowels pronounced with a broad variation of a medium position of the tongue.

Thus altogether there are six groups of English vowel phonemes, which are differentiated according to the vertical movement of the tongue.