Higgins: Tired of listening to sounds?
Pickering: Yes. It’s a fearful strain. I rather fancied myself because I can pronounce twenty-four distinct vowel sounds, but your hundred and thirty beat me. I can’t hear a bit of difference between most of them.
Higgins: Oh, that comes with practice. You hear no difference at first, but you keep on listening and presently you find they’re all as different as A from B.
GEORGE BERNARD SHAW, Pygmalion, 1912
According to Wikipedia [The Free Encyclopedia], the word ‘vowel’ comes from the Latin word vocalis, meaning “vocal” (i.e. relating to the voice). In English, the word vowel is commonly used to mean both vowel sounds and the written symbols that represent them. Middle English: from Old French vouel, from Latin vocalis (littera) ‘vocal (letter)’.
In phonetics, a vowel is a sound in spoken language, with two complementary definitions. In the phonetic definition, a vowel is a sound, such as the English “ah” /ɑː/ or “oh” /əʊ/, produced with an open vocal tract; it is median (the air escapes along the middle of the tongue), oral (at least some of the airflow must escape through the mouth), frictionless and continuant. There is no significant build-up of air pressure at any point above the glottis. This contrasts with consonants, such as the English “sh” [ʃ], which have a constriction or closure at some point along the vocal tract. In the other, phonological definition, a vowel is defined as syllabic, the sound that forms the peak of a syllable. A phonetically equivalent but non-syllabic sound is a semivowel. According to Longman Dictionary of Language Teaching and Applied Linguistics, Fourth edition, by Jack C. RICHARDS and RICHARD SCHMIDT, in which the term ‘vowel’ is defined as:
“A speech sound produced without the significant constriction of the air flowing through the mouth.”
And according to DAVID CRYSTAL who defines ‘vowel’ in his ‘A Dictionary of Linguistics and Phonetics, 6th Edition.’
“One of the two general categories used for the classification of speech sounds, the other being consonant. Vowels can be defined in terms of both phonetics and phonology. Phonetically, they are sounds articulated without a complete closure in the mouth or a degree of narrowing which would produce audible friction; the air escapes evenly over the centre of the tongue…………..From a phonological point of view, vowels are those units which function at the centre of syllables…”
Then, the term ‘vowel’ is also defined by Cambridge Advanced Learner’s Dictionary & Thesaurus, Third Edition, which is published by Cambridge University Press:
“A speech sound produced by humans when the breath flows out through the mouth without being blocked by the teeth, tongue, or lips:”
And HARUKO MOMMA defines the term ‘vowel’ in his ‘Glossary of Linguistic Terms’ as:
“Vowel Refers to speech sounds other than consonants: e.g., [i, u, æ, ɑ]. A vowel is produced without major restriction on the flow of air in the mouth and can comprise the centre of a syllable.”
So, vowels can be represented with regard to the horizontal and vertical tongue position within the oral cavity. If one raises the front of one’s tongue as close to the hard palate as one can without actually reaching it, one produces a close (high) front vowel: [i]. If one lowers the front of one’s tongue as far from the hard palate as possible, one gets an open (low) front vowel: [a]. Now if one divides the distance between the tongue positions for [i] and [a] into three equal parts, one gets the half-close front [e], and the half-open front [Ɛ]. If one does the same movements with the back of one’s tongue, one will get the close back vowel [u], the half-close back [o], the half-open back [ɔ], and the open back [ɑ].
The 8 vowels so obtained are called cardinal vowels. They do not necessarily occur in every language, they should rather be regarded as theoretical vowels or orientation points which indicate the limits within which the tongue can move in the human mouth to produce vowels, and with reference to which all vowels of all languages can be accommodated. The trapezium(a flat shape with four straight sides) formed by the cardinal vowels is called the Cardinal Vowel Chart, see below:
Figure 1: Cardinal Vowel Chart
The most important simple vowels of English are shown in the below chart. They are called simple because the particular tongue position characterizing the vowel in each case is steady throughout producing the vowel. The vowels in the triangle of the chart are central vowels, those on the left of the triangle are front, and those on the right of the triangle are back vowels. The encircled vowels are produced with lip-rounding: they are round vowels. The vowels whose symbols have a colon (:) attached to them are long vowels.
Figure 2: English Simple Vowels
Difference between Vowel and Consonant
Even though all the languages of the world contain both vowels and consonants, and although almost everybody has some idea of whether a given sound is a vowel or a consonant in his language, there is actually more than one way to distinguish between the two classes of sounds. From a phonetic point of view, one way of distinguishing is by considering which sounds have the highest degree of obstruction. Although vowels have almost no obstruction, and some consonants (obstruents, nasals, and the lateral) have a high degree of obstruction, there is a group of consonants (the approximants) which would be classified as vowels if this criterion was used: approximants have no more obstruction than vowels. This can be seen by comparing the approximant [j] in yeast [ji:st] with the vowel [i:] in east [i:st].
From a phonological point of view, it is possible to distinguish between vowels and consonants by testing which sounds may be the nucleus of a syllable, i.e. the part of a syllable that cannot be left out. If one considers a syllable such as [kɑːt] cart, the initial [k] may be left out and one still has a syllable, [ɑːt] art, the final [t] may be left out and one still has a syllable, [kɑː] car. In fact [k] and [t] may both be left out, and the remainder is still a syllable, [ɑː] are. If however, one tries to leave out the vowel, then there is no syllable anymore: [kt]. [a:] is then the sound that cannot be left out. Compare with yeast whereas [j] can be left out, giving [i:st], [i:] cannot:[jst]. Syllabicity seems to be the criterion to determine whether a sound is a vowel or a consonant.
The above discussion would not be complete if one does not mention the problem of so-called syllabic consonants. This is the case when sounds like /r,l,n/ may function as a separate syllable consisting of an only sound, as in /kɒt+n/ cotton or /æp+l/ apple, where English speakers clearly hear two separate syllables. In these words, the /n/ and /l/ seem to function as the nucleus of the second syllable of these words. However, they cannot be classified as vowels, as they can never occur alone as a word.
Articulation of vowels
i. The height of the Tongue (how to open your jaw is in the production of the vowel and how high in the mouth is the tongue):
Depending on the height of the tongue, vowels can be classified into high, mid, and low vowels:
a) High or Close (overall height of tongue is greatest; tongue is closest to roof of mouth): When the front or the back of the tongue is raised towards the roof of the mouth, the vowel is called high, this is the case, for example, in pill, meet, look, or soon. [see the figure 3 (a)]
b) Close-mid, open-mid (intermediate positions) (also: mid / upper-mid / lower-mid). When the tongue occupies the position intermediate between the high and the low one, the vowel is called mid, for example, in get, or the unstressed [ə] in about.
c) Open (overall height of mouth is least; the mouth is most open): When the front or the back of the tongue is as low as possible, the vowel is called low, as, for example, in land, star, or dog. <heed, hid, head, had, father, good, food> [see the figure 3 (b)]
ii. The position of the tongue (how forward your tongue is in the production of the vowel):
Depending on the part of the tongue that is raised most vowels are classified into the front, central and back vowels:
a) Front (tongue is overall forward): When the front part of the tongue is raised towards the hard palate, the vowel is called front, as in meet, get, or land. [see the figure 3 (d)]
b) Central (intermediate position): When the front part of the tongue is raised towards the back part of the hard palate, the vowel is called central, as in about, much, or nurse.
c) Back (tongue is overall back (near pharynx)): When the back part of the tongue is raised towards the soft palate, the vowel is called back, as in star, dog, law, or soon. [see the figure 3 (c)]
a) High b) Low c) Back d) Front
Figure 3: Tongue Height and Tongue Position
These high-low and front-back dimensions of vowel articulation are also referred to as vowel quality (vowel quality is determined by the shape of the mouth when the particular vowel is produced. The shape of the mouth varies according to the position of the tongue and the degree of lip rounding). To illustrate how the articulatory properties of vowels relate to each other, a vowel chart is commonly used as a reference system. The diagram in figure (4) is conventionalized diagram whereas the second diagram in figure (5) complete vowels chart is shown:
Figure 4: Conventionalized Diagram. Figure 5: Vowels Chart
Now, one can consider the height of the tongue and position of the tongue with details.
The upper two diagrams Figure 4 and 5 show that the tongue is high in the mouth in the production of the vowels [i:] and [u:] in the words he [hi:] and who [hu:]. In he the front part (but not the tip) of the tongue is raised; in who it is the back of the tongue. (Prolong the vowels of these words and try to feel the raised part of one’s tongue.) These are both high vowels, and the [i:] is a high front vowel while the [u:] is a high back vowel.
To produce the vowel sound [a:] of hah [ha:], the back of the tongue is low in the mouth, as the lower diagram in Figure 5 shows. (The reason a doctor examining one’s throat may ask anyone to say “ah” is that the tongue is low and easy to see over.) This vowel is, therefore, a low back vowel.
The vowels [ɪ] and [ʊ] in the words hit [hɪt] and put [pʰʊt] are similar to those in heat [hi:t] and hoot [hu:t] with slightly lowered tongue positions.
The vowel [æ] in hack [hæk] is produced with the front part of the tongue low in the mouth, similar to the low vowel [a:], but with the front rather than the back part of the tongue lowered. Say “hack, hah, hack, hah, hack, hah . . .” and one should feel one’s tongue moving forward and back in the low part of one’s mouth. Thus [æ] is a low front vowel.
The vowels [e] and [ɒ] in ten [ten] and got [ɡɒt] (British English) are mid vowels, produced by raising the tongue to a position midway between the high and low vowels just discussed. [ɜː] and [ɔ:] in the words fur [fɜː(r)] and bore [bɔ:r] are also mid vowels, produced with a slightly lower tongue position than [e] and [ɒ], respectively. Here, [e] and [ɜː] are front; [ɒ] and [ɔ:] are back.
To produce the vowel [ʌ] in the word butt [bʌt], the tongue is not strictly high nor low, front nor back and a similar sound of [a:]. So, it is a lower mid-central vowel. The schwa vowel [ə], which occurs as the first sound in about [əbaʊt], or the final sound of sofa [sofə], is also articulated with the tongue in a more or less neutral position between the extremes of high/low, front/back. The schwa is used mostly to represent unstressed vowels. (Everybody can understand the concept of ‘stress’ in my syllable structure assignment)
iii. The position of the lips (whether your lips are rounded in the production of the vowel):
Although the lips can have many different shapes and positions, one will at this stage consider only three possibilities. These are:
a) Rounded, where the corners of the lips are brought towards each other and the lips pushed forwards. This is most clearly seen in [u:].
b) Spread, with the corners of the lips, moved away from each other, as for a smile. This is most clearly seen in [i:].
c) Neutral, where the lips are not noticeably rounded or spread. The noise most English people make when they are hesitating (written ‘er’) has neutral lip position. This is most clearly seen in [a:]. [see the figure 6]
Figure 6: The Position of the Lips
So, vowels may be different from each other with respect to rounding. If one compares [i:] in [tʃi:z] cheese with [u:] in [tʃu:z] choose, one will see that not only is [i:] a front vowel and [u:] a back vowel, but [i:] is also unrounded where [u:] is rounded. When pronouncing [u:] one’s lips are rounded, but when pronouncing [i:] the corners of the mouth are much further apart. [See the above figure 6].
However, /u:/, /ʊ/, /ə/, /ɔ:/, and /ɒ/ are the rounded vowels in English while /i:/, /ɪ/, /e/and /æ/ are the spread vowels but other vowels as /ɜː/, /ʌ/, and /a:/ are the neutral vowels. [See the figure 7].
No lip rounding Lip rounding
Figure 7: Rounding. (MCCARTHY 1967:31)
iv. Tenseness (Tense or Lax vowels):
Vowels have additional classifications which are called tense and lax vowels. In English, tense vowels tend to be long, while lax vowels are short. For instance, the tense vowel /i:/ in a word such as feet has a longer duration than the lax vowel /ɪ/ in fit. But tense and lax vowels have other differences too. While tense vowels can occur in both open and closed syllables, lax vowels are restricted to closed syllables. A closed syllable is a syllable ending with a consonant. In such syllables, one finds either tense or lax vowels:
Tense vowels: read /ri:d/, suit /su:t/, hate /heɪt/, talk /tɔ:k/
Non-tense or Lax vowels: fit /fɪt /, sat /sæt/, help /help/, took /tυk/
Open syllables, in contrast, end in a vowel. Only tense vowels can occur in such syllables: bee /bi:/, sue /su:/, pay /peɪ/, law /lɔ:/
So, one can consider tense and lax between monophthong and diphthong vowels through the below examples:
Tense: i: –beat, eɪ– bait, u:- boot, a: –hah, aɪ- high, aʊ -how, ə -about
Lax: ɪ -bit, e -bet, ʊ -put, ɔ: -bore, ɔɪ -boy, æ –hat, ʌ -hut
Additionally, [a:] is a tense vowel as are the diphthongs [aɪ] and [aʊ], but the diphthong [ɔɪ] is lax as are [ӕ], [ʌ], and of course [ə]. Tense vowels may occur at the ends of words: [si:], [seɪ], [su:], [səʊ], [pa:], [saɪ], and [haʊ] represent the English words see, say, sue, sew, pa, sigh, and how. Lax vowels mostly do not occur at the ends of words; [sɪ], [sɛ], [sʊ], [sæ], [sʌ], and [sə] are not possible words in English. (The one exception to this generalization is lax [ɔ:] and its diphthong [ɔɪ], which occur in words such as [sɔ:] (saw) and [sɔɪ] (soy))
In English, all vowels are voiced (except when whispering), but some languages, such as Japanese, have voiceless vowels as well.
Are the vowels long or short? As one may have seen, there are two types of [i] sound in English placed in two different positions. However for the purpose of description, what is relevant is not the difference of position but that of the perceived length of the vowel. Thus it is said that [i:] is a long vowel and [ɪ] is a short one. The same is valid for [u:]/ [ʊ], [ɜː]/ [ə] and [sɔ:]/ [a]. Symbols for long vowels all have a colon. Phonologically, one can establish the rule such as only long vowels may be the last sound of a syllable, whereas short vowels are always followed by at least a consonant. If one takes away the final [t] from the court, [k ɔ:] is a possible syllable (core) whereas [kɒ] could not possibly occur. (Exceptions from this, these are the three short vowels that occur in completely unstressed syllables, [sɪti, ɪntə, swetə(r)] city, into, sweater).
vii. Nasalization of Vowels (Nasality):
Vowels, like consonants, can be produced with a raised velum that prevents the air from escaping through the nose, or with a lowered velum that permits air to pass through the nasal passage. When the nasal passage is blocked, oral vowels result; when the nasal passage is open, nasal (or nasalized) vowels result. In English, nasal vowels occur for the most part before nasal consonants in the same syllable, and oral vowels occur in all other places. The words bean, bone, bingo, boom, bam, and bang are examples of words that contain nasalized vowels. To show the nasalization of a vowel in a narrow phonetic transcription, an extra mark called a diacritic—the symbol ~ (tilde) in this case—is placed over the vowel, as in bean [bĩn] and bone [bõn].
But there are no nasal vowels in British English, i.e. no vowels in which the air also escapes through the nose. So, nasality is optional. If nothing is said, the vowel is not nasal.
viii. “R”- coloured vowels:
In phonetics, an r-coloured or rhotic vowel (also called a retroflex vowel, vocalic r, or a rhotacized vowel) is a vowel that is modified in a way that results in a lowering in the frequency of the third formant. R-coloured vowels can be articulated in various ways: the tip or blade of the tongue may be turned up during at least part of the articulation of the vowel (a retroflex articulation) or the back of the tongue may be bunched. In addition, the vocal tract may often be constructed in the region of the epiglottis. The r-coloured vowels of General American can be written with “vowel-r” digraphs:
Stressed [ɝ] (more-formal) or [ɚ] (more-common): hearse, assert, mirth, work, turkey, Myrtle
Unstressed [ɚ]: standard, dinner, Lincolnshire, editor, measure, martyr
Stressed [ɑ˞]: start, car
Stressed [ɔ˞]: north, war
In words such as start, many speakers have r-colouring only in the coda of the vowel, rather than as a simultaneous articulation modifying the whole duration. This can be represented in IPA by using a succession of two symbols such as [ɑɚ] or [ɑɹ], rather than the unitary symbol [ɑ˞]. Dialects of English differ in how many vowel sounds are distinct before [ɹ], for example, mary, merry, marry. In British English, the final “r” has been lost and replaced with a schwa, for example. [ɪə] for ‘ear’.
Classification of vowels
(on the basis of their manner of Articulation)
In establishing the vowel system of a language, several further dimensions of classification may be used. One criterion is in terms of the duration of the vowel (whether relatively ‘long’ or ‘short’ vowels are used). Another is whether, during an articulation, there is any detectable change in quality. If the quality of a vowel stays unchanged, the term pure vowel, or monophthong, is used, for example, the standard British pronunciation of red, car, sit, seat. If there is an evident change in quality, one talks instead of a gliding vowel. If two auditory elements are involved, the vowel glide is referred to as a diphthong, for example, light, say, go; if three elements, as a triphthong, for example, fire, hour (in some pronunciations). In the distinctive feature theory of phonology, the term vocalic is used as the main feature in the analysis of vowel sounds. So, one can consider these classifications with details:
i. Monophthongs or Pure vowels. (From Greek monophthongs, from monos ‘singleʼ + phthongos ‘soundʼ):
A term used in the phonetic classification of vowel sounds on the basis of their manner of articulation: it refers to a vowel (a pure vowel) where there is no detectable change in quality during a syllable, as in English cart, cut, cot. In some dialect and diachronic studies, a process of monophthongization can be found, i.e. a change in vowel quality from a diphthong to a monophthong and English has 12 of them. One can understand the description of English monophthong vowels in the following lines:
a) English short vowels:
English has a large number of vowel sounds; the first ones to be examined are short vowels and each vowel is described in relation to the cardinal vowels. [See the above figure 5].
ɪ sit/sɪt/ Short high front unrounded monophthong
e ten/ten/ Short mid front unrounded monophthong
æ cat/kæt/ Short low front unrounded monophthong
ʌ cup/kʌp/ Short low central unrounded monophthong
ɒ got/ɡɒt/ (British English) Short low back rounded monophthong
ʊ put/pʊt/ Short high back rounded monophthong
ə about/əˈbaʊt/ Short mid central unrounded monophthong
b) English long vowels:
English has a large number of vowel sounds; the second ones to be introduced here are the five long vowels; these are the vowels which tend to be longer than the short vowels in similar contexts. [See the above figure 5].
iː see/siː/ Long high front unrounded monophthong
ɑː father/ˈfɑːðə(r)/ Long low back unrounded monophthong
ɔː saw/sɔː/ Long mid back rounded monophthong
uː too/tuː/ Long high back rounded monophthong
ɜː fur/fɜː(r)/ Long mid central unrounded monophthong
ii. Diphthongs [from Greek diphthongos, from di- ‘twiceʼ + phthongos ‘voice, soundʼ.]:
A term used in the phonetic classification of vowel sounds on the basis of their manner of articulation: it refers to a vowel where there is a single (perceptual) noticeable change in quality during a syllable, as in English beer, time, loud. The vowels described so far have all been monophthongs, such vowels are called monophthongs (where no qualitative change is heard), and English has 12 of them. In contrast to the diphthongs (or gliding vowels), where the tongue moves from one position to another. English also has 8 diphthongs, which are vowels that change character during their pronunciation, that is, they begin at one place and move towards another place. Examples can be found in a day, fight, oil, so, and now for the so-called closing diphthongs, while centring diphthongs occur, for example, in bare, beer, and sure. So, a diphthong is a complex vowel during the production of which one tongue position is changed into another but no new syllable is formed and it can be analyzed as a sequence of two vowels or a vowel + glide. For example, the vowels in the words height, hate, house, hose. Therefore, another word goal is written [əʊ], as in [gəʊl] goal, with two symbols, one for how it starts and one for how it ends.
Figure 8: Diphthongs.
The easiest way to remember them is in term of three groups composed as follow:
According to different theoretical criteria, a diphthong can be considered a single (‘unit’) phoneme or a combination of two phonemes. The terms ‘rising’ and ‘falling’ are used to describe diphthongs in two different ways:
a) If the first phase is more open (closed vs open) than the second, it is a rising diphthong, as in the examples above. If the first phase is more closed, it is falling, for example, in Fr. bois ‘woods.
b) In a different terminology, a diphthong is said to be rising if the first element carries less stress than the second, as in Span. país ‘country’; it is falling if the first element carries greater stress, as in the English examples above. There is much debate about whether diphthongs in English consist of two vowels or of one vowel and one glide. Numerous orthographic conventions prevail, for example, [aυ] [au], [āυw].
Other classifications of diphthongal types exist, in terms of the extent of their movement (for example, whether it is ‘wide’ or ‘narrow’) and their direction (whether the diphthong is ‘centring’ or not, i.e. ending with a central vowel). Diphthongization is the term used to describe a process where a monophthong has become a diphthong (has been diphthongized), as in cases of historical or dialect change. Diphthongs are transcribed using symbols which represent the extremes of vowel movement between the two positions, as in [aI] for the unit in fine.
iii. Triphthongs (from French triphtongue, from tri- ‘threeʼ, on the pattern of a diphthong):
A term used in the phonetic classification of vowel sounds on the basis of their manner of articulation: it refers to a type of vowel where there are two noticeable changes in quality during a syllable, as in a common pronunciation of English fire and tower /faɪə/ and /taʊə/. The distinction between triphthongs and the more common diphthongs is sometimes phonetically unclear. Note that some people speak of triphthongs for groups of diphthongs + schwa (ə) for example, mower /ˈməʊə(r)/. So, the triphthongs can be looked on as being composed of the five closing diphthongs described in the last section, with ə added on the end. Thus, one can get with examples:
eɪ+ə=eɪə > layer /ˈleɪə(r)/ , player /ˈpleɪə(r)/
əʊ+ə=əʊə > lower /ˈləʊə(r)/ , mower /ˈməʊə(r)/
aɪ+ə=aɪə > liar /ˈlaɪə(r)/ , fire /ˈfaɪə(r)/
ɔɪ+ə=ɔɪə > loyal /ˈlɔɪəl/ , royal /ˈrɔɪəl/
aʊ+ə =aʊə > power /ˈpaʊə(r)/ , hour /ˈaʊə(r)/
iv. Semivowel (from semi- + vowel, on the pattern of Latin semivocalis):
In phonetics and phonology, a semivowel (or glide) is a sound, such as English /w/ or /j/ that is phonetically similar to a vowel sound but functions as the syllable boundary rather than as the nucleus of a syllable or a speech sound intermediate between a vowel and a consonant, for example, w or y. Semivowels are glides like /w/ and /j/ that act as part of a diphthong, so in conjunction with a vowel sound. In practice, only those semivowels that precede the vowel count as a consonant, not those that follow it where they count as a vowel.
So, the words wet and yet are pronounced with a consonant glide at their fronts, and this is referred to as a semivowel because they start with a consonant sound. Contrast this with cow and coy where there is no consonant property involved, so those are purely vocalic: they end in a vowel sound, not in a consonant sound. Spelling may or may not reflect this, though, because English spelling derives at best from the sounds of English that were spoken five to nine centuries ago, not from the sounds of English today. That is why it is pointless to talk about letters. One has a false premise here: there is no semivowel in the word cry, only a purely vocalic, garden-variety diphthong. The y in cry /kraɪ/ represents a falling diphthong /aɪ/, whereas the one is in yes/jɛs/ is the semi-vocalic glide /j/ one is looking for, being the first element of a rising diphthong /jɛ/. Similarly in few /fju/.
Semi-vowels are things like /w/ and /j/, and they are frequently talked about only in rising diphthongs in English where they take on a consonant character. So cow has /kaʊ/ while coward has /ˈkaʊɚd/, which can also be written /ˈkawɚd/. Similarly, the noun toe and verb tow have /tou/, which can also be written /tow/. In concrete phonetics, one may see narrow transcriptions like [tʰo̞ʊ̯]. A semivowel at the start of the rising diphthong does not usually count as part of the syllable’s rime so yet /jɛt/ rhymes with bet /bɛt/. Similarly, the glide in queen /kwin/, [kʰwi:n] does not count for rhyming, allowing it to rhyme with seen /sin/ and machine /məˈʃin/.
However with the /ju/ diphthong, some poets prefer to include the leading semivowel, preferring to rhyme cute /kjut/ with dispute /dɪˈspjut/ instead of with words lacking that /j/ component like shoot /ʃut/. So for them the vowel is the entire diphthong /ju/ including its leading semi-vowel and not just /u/, since they are trying to rhyme with /jut/ not just with /ut/.
v English Phonetics and Phonology, Fourth Edition by PETER ROACH
v Phonetics and Phonology by CLAIRE-A. FOREL and GENOVEVA PUSKÁS
v Introducing English Linguistics by CHARLES F. MEYER.
v An Introduction to Language, 9th Edition by Victoria FROMKIN, ROBERT RODMAN and NINA HYAMS
v Introduction to English Language & Linguistics by LÁSZLÓ VARGA
v The Handbook of English Linguistics Edited by BAS AARTS AND APRIL MCMAHON
v Longman Dictionary of Language Teaching and Applied Linguistics, Fourth Edition, by Jack C. RICHARDS and RICHARD SCHMIDT.
v A Dictionary of Linguistics and Phonetics 6th Edition.’ By DAVID CRYSTAL.
v Oxford Advanced Learner’s Dictionary 9th Edition, published by OALD
v ANDROID MOBILE APPS (only for education)
v Various Education Websites for Online Search like Wikipedia.com