Vietnamese phonology

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This article is a technical description of the sound system of the Vietnamese language, including phonetics and phonology. Two main varieties of Vietnamese, Hanoi and Ho Chi Minh City, are described below.

Initial consonants

Initial consonants which exist only in the Hanoi dialect are in red, while those that exist only in the Saigon dialect are in blue.

		Labial	Dental/ Alveolar	Retroflex	Palatal	Velar	Glottal
Nasal		m	n		ɲ	ŋ
Stop/ Affricate	plain	(p)	t	ʈʂ	c	k	(ʔ)
	aspirated		tʰ
	glottalized	ɓ	ɗ
Fricative	plain	f	s	ʂ		x	h
	voiced	v	z	ʐ		ɣ
Approximant			l		j	w

• /p/ occurs syllable-initially only in loan words, and is mostly converted into /ɓ/ (as in sâm banh, derived from French champagne).
• /m, ɓ/ are bilabial, while /f, v/ are labiodental.
• The glottalized stops are preglottalized and voiced: [ʔɓ, ʔɗ] (i.e., the glottis is always closed before the oral closure). This glottal closure is often not released before the release of the oral closure, resulting in the characteristic implosive pronunciation. However, sometimes the glottal closure is released prior to the oral release in which case the stops are pronounced [ʔb, ʔd]. Therefore, the primary characteristic is preglottalization with implosion being secondary.
• /tʰ, t/ are denti-alveolar ([t̪ʰ, t̪]), while /ɗ, n/ are apico-alveolar.
• /c, ɲ/ are phonetically lamino-palatoalveolar (i.e. the blade of the tongue makes contact behind the alveolar ridge).
• /c/ is often slightly affricated [t͡ɕ], but it is unaspirated. (Note that the English affricate is aspirated [t͡ʃʰ] and usually apical, unlike Vietnamese).
• A glottal stop [ʔ] is inserted before words that begin with a vowel, and additionally before /w/ in the Hanoian dialect:

ăn	'to eat'	/ăn/	→	[ʔăn]
uỷ	'to delegate'	/wi/	→	[ʔwi]

Hanoi

• /ʐ/ and /j/ exist only in loan words.
• /s, z/ are dentalized laminal alveolar: [s̪, z̪].
• /l/ is apico-alveolar.
• /w/ can form consonant clusters with other consonants except labial consonants.

Ho Chi Minh City (Saigon)

• /v/ is generally pronounced [j] in informal speech, but the speakers generally pronounce [v] when they read a text. It is always pronounced [v] in loan words (va li, ti vi etc.), even in informal speech. There is [vj, bj, βj] that is also present among other speakers. These pronunciations are remnants of a merger and sound change involving /v/ in southern speech (but /v/ is always present in the northern and central regions).
• Some speakers don't distinguish /s/ and /ʂ/.
• Some speakers don't distinguish /c/ and /tʂ/.
• Some speakers pronounce d as [j], and gi as [z], many speakers pronounce both as [j].
• /s/ is apico-alveolar.
• /l/ is lamino-palatoalveolar: [lʲ].
• In southern speech, the phoneme /ʐ/ has a number of variant pronunciations that depend on the speaker. More than one pronunciation may even be found within a single speaker. It may occur as a retroflex fricative [ʐ], an alveolar approximant [ɹ], a flap [ɾ], a trill [r], or a fricative tap/trill [ɾ̞, r̝]. This sound is generally represented in Vietnamese linguistics by the letter ⟨r⟩.
• /w/ cannot form consonant clusters.

Reduction of consonant clusters

In the Saigonese dialect, all initial consonant + /w/ clusters have been reduced:

• After velars and glottals (except /x/), the velar is dropped:

hu	/hw/	→	u	/w/
qu	/kw/	→	u	/w/
ngu	/ŋw/	→	u	/w/

• /xw/ (khu) becomes /f/ (ph).

• After coronals (including retroflexes and palatals), the onglide is dropped:

tu	/tw/	→	t	/t/
xu	/sw/	→	x	/s/
lu	/lw/	→	l	/l/

Comparison of initials

In Hanoian Vietnamese, d, gi and r are all pronounced [z], while x and s are both pronounced [s]. The table below summarizes these sound correspondences:

Syllable onsets
Hanoi	Saigon	Example
		word	Hanoi	Saigon
/v/	/j/	vợ   'wife'	/və˨˩ˀ/	/jə˨˧/
/z/		da   'skin'	/za˧/	/ja˧/
	/ʐ/	ra   'to go out'		/ʐa˧/
/c/	/c/	chẻ   'split'	/cɛ˧˩/	/cɛ˩˥/
	/tʂ/	trẻ   'young'		/tʂɛ˩˥/
/s/	/s/	xinh   'beautiful'	/siŋ˧/	/sɨn˧/
	/ʂ/	sinh   'born'		/ʂɨn˧/

Vowels

Vowel nuclei

	Front	Central	Back
Centering	/iə̯/ ⟨ia~iê⟩	/ɨə̯/ ⟨ưa~ươ⟩	/uə̯/ ⟨ua~uô⟩
Close	/i/ ⟨i, y⟩	/ɨ/ ⟨ư⟩	/u/ ⟨u⟩
Close-mid	/e/ ⟨ê⟩	/ə/ ⟨ơ⟩ /ə̆/ ⟨â⟩	/o/ ⟨ô⟩
Open-mid	/ɛ/ ⟨e⟩		/ɔ/ ⟨o⟩
Open		/a/ ⟨a⟩ /ă/ ⟨ă⟩

The IPA chart of vowel nuclei to the right is based on the sounds in Hanoi Vietnamese, (i.e., other regions of Vietnam may have different inventories). Vowel nuclei consist of monophthongs (i.e., simple vowels) and three centering diphthongs.

• All vowels are unrounded except for the three back rounded vowels: /u, o, ɔ/.
• /ə̆/ and /ă/ are pronounced short — shorter than the other vowels.
• While there are small spectral differences between /ə̆/ and /ə/, it has not been established that they are perceptually significant.
• /ɨ/: Many descriptions, such as Thompson, Nguyễn (1970), Nguyễn (1997), consider this vowel to be close back unrounded: [ɯ]. However, Han's instrumental analysis indicates that it is more central than back. Hoang (1965), Brunelle (2003) and Phạm (2006) also transcribe this vowel as central.
• According to Hoang (1965), /ə, ə̆, a/ are phonetically central [ɘ, ɐ, ä], whereas /ă/ is back [ɑ].
• Thompson (1965) notes that in Hanoi the diphthongs, iê /iə̯/, ươ /ɨə̯/, uô /uə̯/, may be pronounced [ie̯, ɨə̯, uo̯], respectively (as the spelling suggests), but before /k, ŋ/ and in open syllables these are always pronounced [iə, ɨə, uə].
• In Southern Vietnamese, the high and upper-mid vowels /i, ɨ, u, e, ə, o/ are diphthongized in open syllables: [ɪi̯, ɯ̽ɯ̯, ʊu̯, ɛe̯, ʌɤ̯, ɔo̯]:

chị	('elder sister')	/ci/	→	[cɪi̯]		quê	('countryside')	/we/	→	[wɛe̯]
tư	('fourth')	/tɨ/	→	[tɯ̽ɯ̯]		mơ	('to dream')	/mə/	→	[mʌɤ̯]
thu	('autumn')	/tʰu/	→	[tʰʊu̯]		cô	('paternal aunt')	/ko/	→	[kɔo̯]

Closing sequences

In Vietnamese, vowel nuclei are able to combine with offglides /j/ or /w/ to form closing diphthongs and triphthongs. Below is a chart listing the closing sequences of general northern speech.

	/w/ offglide		/j/ offglide
	Front	Central		Back
Centering	/iə̯w/ ⟨iêu⟩	/ɨə̯w/ ⟨ươu⟩	/ɨə̯j/ ⟨ươi⟩	/uə̯j/ ⟨uôi⟩
Close	/iw/ ⟨iu⟩	/ɨw/ ⟨ưu⟩	/ɨj/ ⟨ưi⟩	/uj/ ⟨ui⟩
Close-mid	/ew/ ⟨êu⟩	– /ə̆w/ ⟨âu⟩	/əj/ ⟨ơi⟩ /ə̆j/ ⟨ây⟩	/oj/ ⟨ôi⟩
Open-mid	/ɛw/ ⟨eo⟩			/ɔj/ ⟨oi⟩
Open		/aw/ ⟨ao⟩ /ăw/ ⟨au⟩	/aj/ ⟨ai⟩ /ăj/ ⟨ay⟩

Thompson (1965) says that in Hanoi, words spelled with ưu and ươu are pronounced /iw, iəw/, respectively, whereas other dialects in the Tonkin delta pronounce them as /ɨw/ and /ɨəw/. Hanoi speakers that do pronounce these words with /ɨw/ and /ɨəw/ are using only a spelling pronunciation.

Final stops

When stops /p, t, k/ occur at the end of words, they have no audible release ([p̚, t̚, k̚]):

đáp	'to reply'	/ɗap/	→	[ɗap̚]
mát	'cool'	/mat/	→	[mat̚]
khác	'different'	/xak/	→	[xak̚]

When the velar consonants /k, ŋ/ follow [w] (Hanoi) or /u, o/ (Saigon), they are articulated with a simultaneous bilabial closure [k͡p̚, ŋ͡m] (i.e. doubly articulated) or are strongly labialized [kʷ̚, ŋʷ].

đục	'muddy'	/ɗuk/	→	[ɗɨ̆wk͡p̚], [ɗuk͡p̚]
độc	'poison'	/ɗok/	→	[ɗə̆wk͡p̚], [ɗok͡p̚]
ung	'cancer'	/uŋ/	→	[ʔɨ̆wŋ͡m], [ʔuŋ͡m]

Hanoi finals

Diphthongization

Old Vietnamese rimes ending with velar consonants have been diphthongized in the Hanoian dialect:

ong, oc	/ɔŋ/, /ɔk/	→	[ăwŋ͡m], [ăwk͡p̚]
ông, ôc	/oŋ/, /ok/	→	[ə̆wŋ͡m], [ə̆wk͡p̚]
ung, uc	/uŋ/, /uk/	→	[ɨ̆wŋ͡m], [ɨ̆wk͡p̚]
anh, ach	/ɛŋ/, /ɛk/	→	[ăjŋ̟], [ăjk̟]
ênh, êch	/eŋ/, /ek/	→	[ə̆jŋ̟], [ə̆jk̟]
inh, ich	/iŋ/, /ik/	→	[ɨ̆jŋ̟], [ɨ̆jk̟]

The monophthongal variants are now mainly heard in the Nghệ An, Hà Tĩnh and a few South Central Coast dialects, and have been diphthongized in most Northern varieties.

Analysis of final ch, nh

The pronunciation of syllable-final ch and nh in Hanoi Vietnamese has had different analyses. One analysis, that of Thompson (1965) has them as being phonemes /c, ɲ/, where /c/ contrasts with both syllable-final t /t/ and c /k/ and /ɲ/ contrasts with syllable-final n /n/ and ng /ŋ/. Final /c, ɲ/ is, then, identified with syllable-initial /c, ɲ/.

Another analysis has final ⟨ch⟩ and ⟨nh⟩ as representing predictable allophonic variants of the velar phonemes /k/ and /ŋ/ that occur after upper front vowels /i/ (orthographic ⟨i⟩) and /e/ (orthographic ⟨ê⟩). This analysis interprets orthographic ⟨ach⟩ and ⟨anh⟩ as an underlying /ɛ/, which becomes phonetically open and diphthongized: /ɛk/ → [ăjk̟], /ɛŋ/ → [ăjŋ̟].

Arguments for the second analysis include the limited distribution of final [c] and [ɲ], the gap in the distribution of [k] and [ŋ] which do not occur after [i] and [e], the pronunciation of ⟨ach⟩ and ⟨anh⟩ as [ɛc] and [ɛɲ] in certain conservative central dialects, and the patterning of [k]~[c] and [ŋ]~[ɲ] in certain reduplicated words. Additionally, final [c] is not usually articulated as far forward as the initial [c]: [c] and [ɲ] are pre-velar [k̟, ŋ̟].

The first analysis closely follows the surface pronunciation of a slightly different Hanoi dialect than the second. In this dialect, the /a/ in /ac/ and /aɲ/ is not diphthongized but is actually articulated more forward, approaching a front vowel [æ]. This results in a three-way contrast between the rimes ăn [æ̈n] vs. anh [æ̈ɲ] vs. ăng [æ̈ŋ]. For this reason, a separate phonemic /ɲ/ is posited.

Saigon finals

While the variety of Vietnamese spoken in Hanoi has preserved finals faithfully from old Vietnamese, the variety spoken in Saigon has drastically changed its finals. There were two steps in the development of rimes in the Saigonese dialect from old Vietnamese. In the first step, -ch and -nh merged with -t and -n, while rimes ending in /t, n/ except after /i, e/ merged with /k, ŋ/. In the second step, vowels in alveolar rimes became centralized, analogous to the diphthongization in the Hanoian dialect.

Comparison of finals

Below is a table of rimes ending in /n, t, ŋ, k/ for the Hanoian dialect:

	/ă/	/a/	/ɛ/	/ɔ/	/ə̆/	/ə/	/e/	/o/	/i/	/ɨ/	/u/	/iə̯/	/ɨə̯/	/uə̯/
/n/	ăn	an	en	on	ân	ơn	ên	ôn	in	ưn	un	iên	ươn	uôn
/t/	ăt	at	et	ot	ât	ơt	êt	ôt	it	ưt	ut	iêt	ươt	uôt
/ŋ/	ăng	ang	anh	ong	âng	–	ênh	ông	inh	ưng	ung	iêng	ương	uông
/k/	ăc	ac	ach	oc	âc	–	êch	ôc	ich	ưc	uc	iêc	ươc	uôc

In the Saigonese dialect, /k, ŋ/ and /t, n/ are only distinguished after /a, ə, ɨ/ and do not occur after /i, e/:

	/ă/	/a/	/ɛ/	/ɔ/	/ə̆/	/ə/	/o/	/ɨ/	/u/	/iə̯/	/ɨə̯/	/uə̯/
/n/		anh				ên ênh		in inh
/t/		ach				êt êch		it ich
/ŋ/	ăn ăng	an ang	en	on ong	ân âng	ơn	ôn ông	ưn ưng	un ung	iên iêng	ươn ương	uôn uông
/k/	ăt ăc	at ac	et	ot oc	ât âc	ơt	ôt ôc	ưt ưc	ut uc	iêt iêc	ươt ươc	uôt uôc

Tone

Vietnamese vowels are all pronounced with an inherent tone. Tones differ in

• pitch
• length
• contour melody
• intensity
• phonation (with or without accompanying constricted vocal cords)

Unlike many Native American, African, and Chinese languages, Vietnamese tones do not rely solely on pitch contour. Vietnamese often uses instead a register complex (which is a combination of phonation type, pitch, length, vowel quality, etc.). So perhaps a better description would be that Vietnamese is a register language and not a "pure" tonal language.

In Vietnamese orthography, tone is indicated by diacritics written above or below the vowel.

Six-tone analysis

There is much variation among speakers concerning how tone is realized phonetically. There are differences between varieties of Vietnamese spoken in the major geographic areas (i.e. northern, central, southern) and smaller differences within the major areas (e.g. Hanoi vs. other northern varieties). In addition, there seems to be variation among individuals. More research is needed to determine the remaining details of tone realization and the variation among speakers.

Northern varieties

The six tones in the Hanoi and other northern varieties are:

Tone name	Tone ID	Description	Chao Tone Contour	Diacritic	Example
ngang "level"	A1	mid level	˧ (33)	(no mark)	ba ('three')
huyền "hanging"	A2	low falling (breathy)	˨˩ (21) or (31)	`	bà ('lady')
sắc "sharp"	B1	mid rising, tense	˧˥ (35)	´	bá ('governor')
nặng "heavy"	B2	mid falling, glottalized, short	˧ˀ˨ʔ (3ˀ2ʔ) or ˧ˀ˩ʔ (3ˀ1ʔ)	̣	bạ ('at random')
hỏi "asking"	C1	mid falling(-rising), harsh	˧˩˧ (313) or (323) or (31)	̉	bả ('poison')
ngã "tumbling"	C2	mid rising, glottalized	˧ˀ˥ (3ˀ5) or (4ˀ5)	˜	bã ('residue')

Northern Vietnamese (non-Hanoi) tones as uttered by a male speaker in isolation. From Nguyễn & Edmondson (1998)

Hanoi tones as uttered by a female speaker in isolation. From Nguyễn & Edmondson (1998)

Hanoi tones as uttered by a different female speaker in isolation. From Nguyễn & Edmondson (1998)

Ngang tone:

• The ngang tone is level at around the mid level (33) and is produced with modal voice phonation (i.e. with "normal" phonation). Alexandre de Rhodes (1651) describes this as "level"; Nguyễn (1997) describes it as "high (or mid) level".

Huyền tone:

• The huyền tone starts low-mid and falls (21). Some Hanoi speakers start at a somewhat higher point (31). It is sometimes accompanied by breathy voice (or lax) phonation in some speakers, but this is lacking in other speakers: bà = [ɓa˨˩]. Alexandre de Rhodes (1651) describes this as "grave-lowering"; Nguyễn (1997) describes it as "low falling".

Hỏi tone:

• The hỏi tone starts a mid level and falls. It starts with modal voice phonation, which moves increasingly toward tense voice with accompanying harsh voice (although the harsh voice seems to vary according to speaker). In Hanoi, the tone is mid falling (31). In other northern speakers, the tone is mid falling and then rises back to the mid level (313 or 323). This characteristic gives this tone its traditional description as "dipping". However, the falling-rising contour is most obvious in citation forms or when syllable-final; in other positions and when in fast speech, the rising contour is negligible. The hỏi also is relatively short compared with the other tones, but not as short as the nặng tone. Alexandre de Rhodes (1651) describes this as "smooth-rising"; Nguyễn (1997) describes it as "dipping-rising".

Ngã tone:

• The ngã tone is mid rising (35). Many speakers begin the vowel with modal voice, followed by strong creaky voice starting toward the middle of the vowel, which is then lessening as the end of the syllable is approached. Some speakers with more dramatic glottalization have a glottal stop closure in the middle of the vowel (i.e. as [VʔV]). In Hanoi Vietnamese, the tone starts at a higher pitch (45) than other northern speakers. Alexandre de Rhodes (1651) describes this as "chesty-raised"; Nguyễn (1997) describes it as "creaking-rising".

Sắc tone:

• The sắc tone starts as mid and then rises (35) in much the same way as the ngã tone. It is accompanied by tense voice phonation throughout the duration of the vowel. In some Hanoi speakers, the ngã tone is noticeably higher than the sắc tone, for example: sắc = ˧˦ (34); ngã = ˦ˀ˥ (45). Alexandre de Rhodes (1651) describes this as "acute-angry"; Nguyễn (1997) describes it as "high (or mid) rising".

Nặng tone:

• The nặng tone starts mid or low-mid and rapidly falls in pitch (32 or 21). It starts with tense voice that becomes increasing tense until the vowel ends in a glottal stop closure. This tone is noticeably shorter than the other tones. Alexandre de Rhodes (1651) describes this as "chesty-heavy"; Nguyễn (1997) describes it as "constricted".

Southern varieties

The Southern variety is similar through all tones except for the nặng tone, which is pronounced [˨˧]. Many of those speaking Southern dialects will omit using the ngã tone and replace it with the hỏi tone.

North-central and Central varieties

North-central and Central Vietnamese varieties are fairly similar with respect to tone although within the North-central dialect region there is considerable internal variation.

It is sometimes said (by people from other provinces) that people from Nghệ An pronounce every tone as a nặng tone.

Eight-tone analysis

An older analysis assumes eight tones rather than six. This follows the lead of traditional Chinese phonology. In Middle Chinese, normal syllables allowed for three tonal distinctions, but syllables ending with /p/, /t/ or /k/ had no tonal distinctions. Rather, they were consistently pronounced with in a short high tone, which was called the entering tone and considered a fourth tone. Similar considerations lead to the identification of two additional tones in Vietnamese for syllables ending in /p/, /t/, /k/ or /c/. These are not phonemically distinct, however, and hence not considered as separate tones by modern linguists.

Syllables and phonotactics

According to Hannas (1997), there are 4,500 to 4,800 possible spoken syllables (depending on dialect), and the standard national orthography (Quốc Ngữ) can represent 6,200 syllables (Quốc Ngữ orthography represents more phonemic distinctions than are made by any one dialect).

The Vietnamese syllable structure follows the scheme:

Hanoi: (C₁)(w)V(G|C₂)+T

Saigon: (C₁)V(G|C₂)+T

where

C1 = initial consonant onset w = labiovelar on-glide /w/ V = vowel nucleus

G = off-glide coda (/j/ or /w/) C2 = final consonant coda T = tone.

In other words, a syllable can have an optional consonant onset, an optional on-glide /w/ (Hanoi only), and an optional coda. The vowel nucleus may have an additional off-glide.

More explicitly, the syllable types are as follows:

Syllable	Example	Syllable	Example
V	ê "eh"	wV	uể "sluggish"
VC	ám "possess (by ghosts,.etc)"	wVC	oán "bear a grudge"
VC	ớt "capsicum"	wVC	oắt "little imp"
CV	nữ "female"	CwV	huỷ "cancel"
CVC	cơm "rice"	CwVC	toán "math"
CVC	tức "angry"	CwVC	hoặc "or"

C₁:

Any consonant may occur in as an onset with the following exceptions:

• /p/ does not occur in native Vietnamese words

w:

• does not occur after labial consonants /ɓ, f, v, m, w/
• does not occur after /n/ in native Vietnamese words (it occurs in uncommon Sino-Vietnamese borrowings)
• absent in Saigonese as Saigonese /w/ behaves as an initial consonant

V:

The vowel nucleus V may be any of the following 14 monophthongs or diphthongs: /i, ɨ, u, e, ə, o, ɛ, ə̆, ɔ, ă, a, iə̯, ɨə̯, uə̯/.

G: The offglide may be /j/ or /w/. Together, V and G must form one of the diphthongs or triphthongs listed in the section on Vowels. The offglide cannot be /w/ if the syllable contains a /w/ onglide, except for case of 'khuỷu (tay)' (elbow).

C₂:

The optional coda C₂ is restricted to labial, coronal, & velar stops /p, t, k/ and nasals /m, n, ŋ/.

T:

Syllables are spoken with an inherent tone contour. All tone contours are possible for open syllables (syllables without consonant codas) and closed syllables with nasal codas. If the syllable is closed with labial, coronal, or velar stops /p, t, k/, only 2 contours are possible, that is the sắc and the nặng tone.

Notes

²

Below is a table comparing four linguists' different transcriptions of Vietnamese vowels as well as the orthographic representation. Notice that this article mostly follows Han (1966), with the exception of marking short vowels short.

comparison of orthography & vowel descriptions

Orthography	Wikipedia	Thompson	Han	Nguyễn	Đoàn
i/y	i	iː	i	i	i
ê	e	eː	e	e	e
e	ɛ	ɛː	ɛ	a	ɛ
ư	ɨ	ɯː	ɨ	ɯ	ɯ
u	u	uː	u	u	u
ô	o	oː	o	o	o
o	ɔ	ɔː	ɔ	ɔ	ɔ
ơ	ə	ɤː	ɜː	əː	ɤː
â	ə̆	ʌ	ɜ	ə	ɤ
a	a	æː	ɐː	ɐː	aː
ă	ă	ɐ	ɐ	ɐ	a

Thompson (1965) says that the vowels [ʌ] (orthographic â) and [ɐ] (orthographic ă) are shorter than all of the other vowels, which is shown here with the length mark [ː] added to the other vowels. His vowels above are only the basic vowel phonemes. Thompson gives a very detailed description of each vowel's various allophonic realizations.

Han (1966) uses acoustic analysis, including spectrograms and formant measuring and plotting, to describe the vowels. She states that the primary difference between orthographic ơ & â and a & ă is a difference of length (a ratio of 2:1). ơ = /ɜː/, â = /ɜ/; a = /ɐː/, ă = /ɐ/. Her formant plots also seem to show that /ɜː/ may be slightly higher than /ɜ/ in some contexts (but this would be secondary to the main difference of length).

Another thing to mention about Han's studies is that she uses a rather small number of participants and, additionally, although her participants are native speakers of the Hanoi variety, they all have lived outside of Hanoi for a significant period of their lives (i.e. in France or Ho Chi Minh City).

Nguyễn (1997) has a simpler, more symmetrical description. He says that his work is not a "complete grammar" but rather a "descriptive introduction." So, his chart above is more a phonological vowel chart rather than a phonetic one.

Bibliography

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• Đoàn, Thiện Thuật; Nguyễn, Khánh Hà, Phạm, Như Quỳnh. (2003). A Concise Vietnamese Grammar (For Non-Native Speakers). Hà Nội: Thế Giới Publishers, 2001.
• Earle, M. A. (1975). An acoustic study of northern Vietnamese tones. Santa Barbara: Speech Communications Research Laboratory, Inc.
• Ferlus, Michel. (1997). Problemes de la formation du systeme vocalique du vietnamien. Asie Orientale, 26 (1), .
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External links

• Ngữ âm học
• Vietnamese ESL, Hoc Tieng Anh