Instructor: PHD. NGUYỄN NGỌC VŨ
In phonetics and phonology, phonemes - the smallest units of speech in a language that distinguish one word from another - usually place next to one another by a certain time interval. In other words, each phoneme takes up a period of time. However, to form a Vietnamese word má, for instance, we need not only the phonemes /m/ and /a/ but also sắc tone. Similarly, the English word mother is made of the morphemes /mʌðə/ and the stress in a syllable [ˈmʌ]. The phonetic features just mentioned such as sắc tone and stress cannot be put in the time line as the ordinary phonemes. They, in fact, appear at the same time with those phonemes. In linguistics, these features are called prosodic facts or prosodic features. Specifically, they are tones, stress and intonation. This paper provides a contrastive analysis of the meaning and functions of certain prosodic facts in Vietnamese and English. This analysis of these facts can hopefully propose some useful implications for language learning and translation. Then, we can have an in-depth understanding of prosodic facts, the interesting features in languages.
Prosodic facts in Vietnamese and English
Different scholars may have different descriptions of these tones. The widely cited descriptions about the Vietnamese tones are given by Thompson (1987, p. 20) as follows:
The tone distribution in syllables has a strong relation with the final sound.
In poetry, the six tones of Vietnamese language are divided based on their falling and rising nature into two categories: bằng (flat) and trắc (sharp or non-flat).
For purposes of riming, the tones are divided into two tonal patterns dictated by melodic compatibility: the bằng (flat) or low-pitch group comprises the neutral (ngang) and the low (huyền) tones, and the trắc (sharp) or clipped high-pitch group consists of the high (sắc) and the low-rising (hỏi), the mid-rising (ngã), and the low-stop (nặng) tones. In the bằng scheme vowels may be sustained over a period of time whereas vowels in the trắc group tend to be short and clipped. The riming rule, which requires recurrence of the sound successions as well as membership of the vocalic tones in the same tonal group, insures melodic compatibility of the riming words and avoids cacophony. The offshoot of this prosodic rule is that Vietnamese verses exhibit a melodic quality that is absent in the poetry of non-tonal languages.
Tones are among the most important elements in Lục Bát as well as the other Vietnamese verse forms. The tones of the syllables in lục bát verses should follow the following model:
The odd syllables in lục bát verses don't have to follow the rule, but the even syllables must follow the rule.
I.1.2.2. Tones in reduplication
A type of assimilation known as tonal harmony is involved in Vietnamese reduplication. The rule of this type of reduplication is as follows: bằng tone (flat tone) and trắc tone (sharp tone) of the same register go with each other in the combinations. Element with trắc tone precedes on with trắc tone. Some common instances for this type are: xam xám, hâm hấp, nho nhỏ, đo đỏ, nhàn nhạt, nhè nhẹ…The tones of all reduplicated words are always within the same tonal register (either upper or lower). Take the first example to analyze: xám (gray) with the sắc tone when reduplicated appears as xam xám (grayish) with a ngang-toned reduplicant — both syllables are in the upper tonal register.
I.1.2.3. Tones in idioms
One striking feature of Vietnamese idioms is symmetry. Apart from three-syllable idioms, other idioms made of four or more syllables are usually divided into two parts. In this kind of idioms, two parts of an idiom have a symmetric structure not only in the numbers of syllables but also in tones. This symmetric rule is that: the last syllables of each part carry the opposite tones. The symmetric model is:
… bằng/ … trắc (… flat/ … sharp)
… trắc/ … bằng (… sharp/ … flat)
Đứng núi này/ trông núi nọ. (The grass is always greener on the other side.)
Màn trời/ chiếu đất. (Sky as net, ground as mat.)
Giật đầu cá/ vá đầu tôm. (To rob Peter to pay Paul.)
Việc nhà thì nhác/ việc chú bác thì siêng. (Lazy in house, hardworking in society.)
This symmetry can sometimes spread the second or third… syllable counting from the last syllable.
… bằng trắc/ … trắc bằng (… flat sharp/ … sharp flat)
Xa mặt/ cách lòng. (Out of sight, out of mind.)
… bằng bằng bằng/ … trắc trắc trắc (…flat flat flat/ … sharp sharp sharp)
Treo đầu dê/ bán thịt chó. (Hange the goat head, sell the dog meat.)
… trắc bằng bằng/ … bằng trắc trắc (… sharp flat flat/ … flat sharp sharp)
I.2. Intonation in Vietnamese
Đổ mồ hôi/ sôi nước mắt. (Pour the sweats, boil the tears.)
Intonation is defines as the rise and fall of the voice in speaking, especially as this affects the meaning of what is being said. Generally speaking, we can identify the following intonations:
Rising Intonation means the pitch of the voice increases over time [↗];
Falling Intonation means that the pitch decreases with time [↘];
Dipping Intonation falls and then rises [↘↗];
Peaking Intonation rises and then falls [↗↘].
Together with pauses, intonation is also a means to classify utterances. Besides, its main function is to put the parts of an utterance together, making a meaningful sentence. Intonation is also used to express characteristics of a certain sentence. It plays a role as a real grammar manner. By intonation, listeners can identify the types of that utterance: affirmative, interrogative or causative…
Anh đi? (You go?) [↗] (raising voice) interrogative sentence
Anh đi! (You go!) [↘] request
In many languages, the up movement of intonation usually shows that the clause is not finished while its down movement signs the completeness of the clause. Moreover, the horizontal movement means enumeration e.g. Đây: bàn, ghế, tủ, giường
… (Here: tables, chairs, closets, beds…)
Finally, intonation has a special meaning in expressing all varied feelings. Listeners, through intonation, can know feelings, emotions of speakers: rage, love, irony, happiness, sadness, worry, sulk…
In Vietnamese, intonation usually goes with modals such as à, ư, nhỉ, nhé… Good use of these means can make utterances lively, meaningful and effective.
I.3. Stress in Vietnamese
In linguistics, stress is the relative emphasis that may be given to certain syllables in a word, or to certain words in a phrase or sentence. The term is also used for similar patterns of phonetic prominence inside syllables. The word accent is sometimes also used with this sense. Stress plays a significant key in European languages like Russian, English, and French while its role is faded away by tones in tonal languages, especially Vietnamese. However, it’s not true to say that Vietnamese does not have stress at all.
In Vietnamese, stress is emphasized by intensifying the length of vowels. In other words, stress in Vietnamese is mainly called qualitative accent. In Vietnamese, there are some words which never carry stress (e.g. cái (a/an/the) – modifier). There are, however, words which are strongly stressed, for example: cà khẳng cà khiu, tóe tòe loe. Most of the lexical words carry stress. There are contrastive pairs of words in which stress is the only means to tell them apart. For instance: cho (give) and để (put) are verbs. (Tôi cho anh quyển sách – I give you the book; Nó để khăn trên bàn – He put the towel on the table). If some polysyllable words are put the wrong stress, they will disintegrate; each syllable will become separate, e.g. bảo với = nói theo (verb) and bảo (verb) + với (preposition).
II.1. Intonation in English
Prosodic facts in English
Intonation, a unit of speech bounded by pauses has movement of music and rhythm, associated with the pitch of voice (Roach, 1983, p. 113). Pausing in some sense is a way of packaging the information such that the lexical items put together in an intonation unit form certain psychological and lexic-grammatical realities.
The certain pattern of voice movement is called 'tone'. A tone is a certain pattern, not an arbitrary one, because it is meaningful in discourse. By means of tones, speakers signal whether to refer, proclaim, agree, disagree, question or hesitate, or indicate completion and continuation of turn-taking, in speech.
II.1.1. Fall (A falling tone)
A falling tone is by far the most common used tone of all. It signals a sense of finality, completion, belief in the content of the utterance… A speaker, by choosing a falling tone, also indicates to the addressee that that is all he has to say, and offers a chance (turn-taking) to the addressee to comment on, agree or disagree with, or add to his utterance. However, it is up to the addressee to do either of these. This tone does in no way solicit a response from the addressee. Nonetheless, it would be polite for the addressee to at least acknowledge in some manner or form that he is part of the discourse. Now, let us see the areas in which a failing tone is used.
A falling tone may be used in referring expressions.
I've spoken with the CLEAner.
Questions that begin with wh-questions are generally pronounced with a falling tone
Imperative statements have a falling tone.
Go and see a DOCtor.
Take a SEAT.
II.1.2. Low rise (A rising tone)
This tone is used in genuine 'Yes/No' questions where the speaker is sure that he does not know the answer, and that the addressee knows the answer. Such Yes/No questions are uttered with a rising tone. For instance, consider the following question uttered with a rising tone, the answer of which could be either of the three options below:
A: Isn't he NICE?
B3: I don't know.
II.1.3. High rise (A rising tone)
If the tonic stress is uttered with extra pitch height, as in the following intonation units, we may think that the speaker is asking for a repetition or clarification, or indicating disbelief.
A: I'm taking up TAxidermy this autumn.
king up WHAT?
A: She passed her DRIving test.
B: She PASSED?
II.1.4. Fall rise (followed by Fall)
While the three tones explicated so far can be used in independent, single intonation units, the fourth tone, fail-rise, appears to be generally used in what may be called 'dependent' intonation units such as those involving sentential adverbs, subordinate clauses, compound sentences, and so on. Fall-rise signals dependency, continuity, and non-finality (Cruttenden, 1986 p. 102). It generally occurs in sentence non-final intonation units. Consider the following in which the former of the intonation units are uttered with a fall-rise tone (the slash indicates a pause):
Private enterPRISE / is always EFficient.
A quick tour of the CIty / would be NICE.
PreSUmably / he thinks he CAN.
Usually / he comes on SUNday.
One of the most frequent complex clause types in English is one that has dependent (adverbial or subordinate) clause followed by an independent (main) clause. When such a clause has two intonation units, the first, non-final, normally has a fall-rise while the second
, final, has falling tone. Therefore, the tone observed in non-final intonation units can be said to have a 'dependency' tone, which is fall-rise (The explication of tone patterns as well as some of the examples in this section are largely based on Cruttenden, 1986). Consider the following:
When I passed my REAding test / I was VEry happy.
If you SEE him / give my MESsage.
When the order of complex clause is reversed, we may still observe the pattern fall-rise and fall respectively, as in
I WON'T deliver the goods / unless I receive the PAYment.
The moon revolves around the EARTH / as we ALLknow.
Private enterprise is always EFficient / whereas public ownership means INefficient.
All in all, final intonation units have a falling tone while non-final ones have fall-rise. Consider further complex clauses:
He joined the ARmy / and spent all his time in ALdershot.
My sister who is a NURSE / has ONE child.
This completes the four major tones selected for the framework. As is the case in this section, some of these tones can be used in combination when a syntactic unit (sentence) has more than one intonation unit. This section has reviewed the (fall-rise + fall) and (fall + fall-rise) patterns. In the following two sections, two patterns, namely (fall-rise + low rise) and (fall + fall), are examined respectively.
II.1.5. Fall-rise + Low Rise
Typically this tone pattern involves a dependent clause followed by a Yes/No question. For example:
If I HELPED you / would you try aGAIN?
Despite its DRAWbacks / do you favor it or NOT?
II.1.6. Fall + Fall
A fall tone can be followed by another fall tone when the speaker expects or demands agreement as in tag questions.
It's a bit TOO good to be true / ISN'T it?
Reinforcing adverbials can also have a fall when place utterance finally as an expression of after-thought.
Ann said she'd help as much as she COULD / NATUrally.
If the two actions are part of a sequence of related events, it has (fall + fall) tone pattern, as in the following in which the information in the first intonation unit and the one in the second one do not have dependency:
II.2. Stress in English
She's 28 years OLD / and lives in GiPPSland.
There are languages like English, Italian, Russian and Spanish, where stress is (at least partly) unpredictable. In such languages, otherwise homophonous words may differ only by the position of the stress (e.g. incite and insight in English), and therefore it is possible to use stress as a grammatical device.
At the clausal level, normally, words that carry higher information content in the utterance are given higher stress than those carrying lower input (information) and those that are predictable in the context. It is generally the case that one word is stressed more than any other since it possesses the highest information content for the discourse utterance, that is, it informs the hearer most. The group of words described above are largely from what is called 'content' words as opposed to 'function' words. Content words are nouns, verbs, adjectives, and adverbs while function words are articles, prepositions, conjunctions, and modal auxiliaries. Furthermore, it is content words that are polysyllabic, not function words. This classification conforms to grammatical considerations. The classification we present here from a suprasegmental viewpoint, that is on the basis of being stressed or not, is slightly different from that of grammar. Consider the following:
English does this to some extent with noun-verb pairs such as a récord
vs. to recórd
, where the verb is stressed on the last syllable and the related noun is stressed on the first; record
also hyphenates differently: a réc-ord
vs. to re-córd
. It is common for dialects to differ in their stress placement for some words. For example, in British English
, the word "laboratory" is pronounced with primary stress on the second syllable, while American English stresses the first.
Some speakers make quite complex semantic distinctions in English using secondary stress. For instance, between "paper BAG" as in a bag made of paper, and "PAPer bag" as in a bag for carrying newspapers.
'Primary' and 'secondary' stress are distinguished in some languages. English is commonly believed to have two levels of stress, as in the words cóunterfòil [ˈkaʊntərˌfɔɪl] and còunterintélligence [ˌkaʊntər.ɪnˈtɛlɪdʒəns], and in some treatments has even been described as having four levels, primary, secondary, tertiary, and quaternary, but these treatments often disagree with each other. It is possible to describe English with only one degree of stress, as long as unstressed syllables may occur without vowel reduction.
In English, stress is most dramatically realized on focused or accented words. For instance, consider the dialogue:
"Is it brunch tomorrow?"
"No, it's dinner tomorrow."
In it, the stress-related acoustic differences between the syllables of "tomorrow" would be small compared to the differences between the syllables of "dinner", the emphasized word. In these emphasized words, stressed syllables such as "din" in "dinner" are louder and longer. They may also have a different fundamental frequency, or other properties. Unstressed syllables typically have a vowel which is closer to a neutral position (the schwa), while stressed vowels are more fully realized. In contrast, stressed and unstressed vowels in Spanish share the same quality—unlike English, the language has no reduced vowels.
Stress can also be put on any word in a sentence to make a possible several sentences, for example:
didn't take the test yesterday. (Somebody else did.)
take the test yesterday. (I did not take it.)
I didn't take
the test yesterday. (I did something else with it.)
I didn't take the
test yesterday. (I took a different one.)
I didn't take the test
yesterday. (I took something else.)
I didn't take the test yesterday
. (I took it some other day.)
The possibilities for stress in tone languages are an area of ongoing research, but stress-like patterns have been observed in Mandarin Chinese. They are realized as alternations between syllables where the tones are carefully realized with a relatively large swing in fundamental frequency, and syllables where they are realized "sloppily" with typically a small swing.
Stressed syllables are often perceived as being more forceful than non-stressed syllables. Research has shown, however, that although dynamic stress is accompanied by greater respiratory force, it does not mean a more forceful articulation in the vocal tract.
This section addresses the notion of stress in words as perceived in connected speech. In addition, the existence and discovery of tonic stress is discussed, and the major types of stress are explicated. Four major types of stress are identified:
II.2.1 Tonic tress
An intonation unit almost always has one peak of stress, which is called 'tonic stress', or 'nucleus'. Because stress applies to syllables, the syllable that receives the tonic stress is called 'tonic syllable'. The term tonic stress is usually preferred to refer to this kind of stress in referring, proclaiming, and reporting utterances. Tonic stress is almost always found in a content word in utterance final position. Consider the following, in which the tonic syllable is underlined:
I'm going to London.
I'm going to London for a holiday.
A question does arise as to what happens to the previously tonic assigned syllables. They still get stressed, however, not as much as the tonic syllable, producing a three level stress for utterances. Then, the following is arrived at., where the tonic syllable is further capitalized:
II.2.2. Emphatic stress
I'm going to London for HOliday.
One reason to move the tonic stress from its utterance final position is to assign an emphasis to a content word, which is usually a modal auxiliary, an intensifier, an adverb, etc. Compare the following examples. The first two examples are adapted from. Roach (1983, p. 144).
- It was very BOring. (unmarked)
- It was VEry boring. (emphatic)
+ You mustn't talk so LOUDly. (unmarked)
+ You MUSTN'T talk so loudly. (emphatic)
Some intensifying adverbs and modifiers (or their derivatives) that are emphatic by nature are (Leech & Svartvik, 1975, p. 135): indeed, utterly, absolute, terrific, tremendous, awfully, terribly, great, grand, really, definitely, truly, literally, extremely, surely, completely, barely, entirely, very (adverb), very (adjective), quite, too, enough, pretty, far, especially, alone, only, own, -self.
II.2.3. Contrastive stress
In contrastive contexts, the stress pattern is quite different from the emphatic and non-emphatic stresses in that any lexical item in an utterance can receive the tonic stress provided that the contrastively stressed item can be contrastable in that universe of speech. No distinction exists between content and function words regarding this. The contrasted item receives the tonic stress provided that it is contrastive with some lexical element (notion) in the stimulus utterance. Syllables that are normally stressed in the utterance almost always get the same treatment they do in non-emphatic contexts. Consider the following examples:
a) Do you like this one or THAT one?
b) I like THIS one.
Many other larger contrastive contexts (dialogues) can be found or worked out, or even selected from literary works for a study of contrastive stress. Consider the following examples:
II.2.4. New information stress
She played the piano yesterday. (It was her who...)
She played the piano yesterday. (She only played (not. harmed) ...)
She played the piano yesterday. (It was the piano that...)
She played the piano yesterday. (It was yesterday...)
In a response given to a wh-question, the information supplied, naturally enough, is stressed,. That is, it is pronounced with more breath force, since it is more prominent against a background given information in the question. The concept of new information is much clearer to students of English in responses to wh-questions than in declarative statements. Therefore, it is best to start with teaching the stressing of the new information supplied to questions with a question word:
a) What's your NAME
b) My name's GEORGE.
a) Where are you FROM?
b) I'm from WALES.
a) Where do you LIVE
b) I live
a) When does the school term END
b) It ends
a) What do you DO
b) I'm a STU
The questions given above could also be answered in short form except for the last one, in which case the answers are:
In other words, 'given' information is omitted, not repeated. In the exchange:
a) What's your name?
b) (My name's) George.
The 'new' information in this response is 'George.' The part referring to his name is given in the question, so it may be omitted.
Regarding the significance of new information declarative statements, Ladefoged (1982, p. 100) states:
'In general, new information is more likely to receive a tonic accent than material that has already been mentioned. The topic of a sentence is less likely to receive the tonic accent than the comment that is made on the topic.'
Comparison between Vietnamese and English prosodic facts and the implications for language learning and translation
Based on detailed descriptions of Vietnamese and English prosodic facts mentioned above, we can have a contrastive view of them in terms of tones, intonation and stress. Then, it can shed a light on language learning and translation.
One of the phonetic typological differences between Vietnamese and English is that Vietnamese is a tonal language in which the pitch levels are used to distinguish words while English is a non-tonal language. In other words, it is tones that make Vietnamese a unique language. Tones are typical features of Vietnamese and some similar tonal languages such as Chinese and Thai. In contrast, English, Russian, French and some other Indo-European languages are not tonal languages and the function of tone is much more difficult to define than in a tone language. That is a reason why most of the foreigners find Vietnamese a difficult language in writing and speaking. Similarly, Vietnamese people usually make mistakes of some English words’ pronunciation. However, knowing the similarities and differences between English and Vietnamese can help learners study these two languages easily and effectively. I once read the collection of short stories “Tớ là Dâu” (“I am Strawberry) by Mr. Joe, a Canadian well-known in Vietnam for his blog writing style in Vietnamese. It is hard to believe that a foreigner who has just been living in Vietnam for three years can speak and write Vietnamese as correctly and fluently as a native Vietnamese. I am really impressed by his humorous writing style as well as the way he uses Vietnamese. In one of his entries, he wrote: “Mọi đường nét của âm thanh đều biến dạng. Tiếng Việt là ngôn ngữ hẻo lánh. Đã thế lại rất oái ăm, bởi nó có đến sáu thanh. Chỉ nhầm một tí là đi một dặm.” (“Every tone has different shapes. Vietnamese is an isolated language. Awkwardly, it has six tones. A miss is as good as a mile.”) Underlying his entries is his careful selection of each Vietnamese word and his appreciation towards Vietnamese. However, not many Vietnamese people nowadays can preserve the traditional beauty of our language. Teen languages or chat languages have been invading our conventional language in specific and our traditional culture in general. Contrasting different languages is at first to have a deeper understanding of our own language, to treasure it, to use it appropriately and to keep its pure beauty intact, then to have strategies for the acquisition of other languages.
Additionally, in English, as in many other European languages, the intonation may function as the only means of distinguishing various types of sentences, for example: He is coming. versus He is coming? In Vietnamese, in contrast, intonation is rarely used as a way to form questions. On one hand, if an assertive statement ends in a word with the high-rising tone, the voice should be raised at the end of the sentence, for example: Hôm nay trời nóng lắm. (It is really hot today.) On the other hand, if a question ends in a word with the low-falling tone, the voice should be lowered at the end of the question, for example: Hôm nay trời nóng lắm à? (Is it really hot today?) In many European languages, like English, the pitch of voice in an assertive statement is usually dropped at the end. In Vietnamese, the meanings of the sentences Ông ấy đi tu. (He has become a Buddhist monk.) and Ông ấy đi tù. (He has been sent to prison.) are completely different. Thus, learners’ attention should be drawn to the fact that the Vietnamese language uses certain grammatical patterns for assertive, negative and interrogative forms. Intonation in Vietnamese is strictly restricted by the tones.
Last but not least, the key difference lies in the fact that Vietnamese is a syllable-timed language in which the rhythm appears to be fairly even, which each syllable giving the impression of having about the same duration and force as any other. English, in contrast, is a stress-timed language in which stressed syllables recur at intervals. In other words, stress is an essential feature of word identity in English (Kenworthy, 1987, p. 18). It, meanwhile, plays an insignificant role in Vietnamese. That is a reason why we cannot translate a Vietnamese poem into an English version in a perfect way. The difficulties for the translation lie in the fact that if we translate word for word, we may not keep the original content of the poem or that if we translate according to its meaning, the translated version may lack the natural rhythm of the original one. Take the Tale of Kieu by Nguyen Du as an example:
Trăm năm trong cõi người ta,
Chữ tài chữ mệnh khéo là ghét nhau.
Trải qua một cuộc bể dâu,
Những điều trông thấy mà đau đớn lòng.
Lạ gì bỉ sắc tư phong,
Trời xanh quen thói má hồng đánh ghen.
“Truyện Kiều” – Nguyễn Du
There have been a lot of translated versions for the stanza above. One of them is:
Within the span of hundred years of human existence,
what a bitter struggle is waged between genius and destiny!
How many harrowing events have occurred while mulberries cover the conquered sea!
Rich in beauty, unlucky in life!
Strange indeed, but little wonder,
since casting hatred upon rosy cheeks is a habit of the Blue Sky.
Translation from Lê Xuân Thuy – “Kim Vân Kiều” (page 19), Second Edition, 1968
Though this translated version can express the full idea of the original poem, it cannot reach the Vietnamese rimming style.
Vladislav Zhukov's version (2004), however, can reproduce the same rhyme schemeof the original without missing its meaning:
Were full five-score the years allotted to born man,
How oft his qualities might yield within that span
to fate forlorn
In time the mulberry reclaims the sunk sea-bourn
And what the gliding eye may first find fair weighs mournful
on the heart
Uncanny? Nay--lack ever proved glut's counterpart
And mindful are the gods on rosy cheeks to dart
celestial spite ...
Thus, in order to have a successful translation, we should take into consideration the distinguished phonetic features of each language such as tonal and rhythm system.
In conclusion, prosodic facts - parts of suprasegmental phonology, together with segmental phonologic phonemes, play a key role in the formation of languages in general. Specifically, a contrastive analysis of prosodic facts in Vietnamese and English help us have some informative ideas about their descriptions and functions. Therefore, we can apply them in our process of acquiring new languages and studying our own language. I hope this paper, to a certain extent, can be useful for your language teaching and learning.
Le, Q.T. (2004). Nghien cuu doi chieu cac ngon ngu. Hanoi: National University Publishing House.
Mai, N.C., Vu, D.N., & Hoang, T.P. (2007). Co so ngon ngu hoc va tieng Viet. Ho Chi Minh City: Education Publishing House.
Ngo, B. N. (2002). The Vietnamese Language Learning Framework. Harvard University, Cambridge, MA.
Roach, P. (2000). English Phonetics and Phonology. Cambridge, UK: Cambridge University Press.
Pham, A.H. (2003). Vietnamese tone: A new analysis. New York, NY: Roudedge.
Jannedy, S. (2007). Prosodic focus in Vietnamese. Humboldt University of Berlin, Berlin, Germany.
Oatlamoe, G.S.S. (2001). Sound system in Vietnamese. Retrieved from http://www.de-han.org/vietnam/chuliau/lunsoat/sound/4.htm
Celik, M. (2001). Teaching English Intonation to EFL/ESL Students. Retrieved from http://iteslj.org/Techniques/Celik-Intonation.html
Ruelle, J. (2007). To la Dau. Ho Chi Minh City: Kim Dong Publishing House.