1.1 Stress, stresslessness, and stress in tone languages

There is a certain conceptual vagueness in the use of the term stress in the literature on Vietnamese. To avoid further confusion, Hyman's (Reference Hyman2006) definition of stress-accent will be adopted in this paper. Primary stress (or just stress, for convenience) is an indication of

Words can also bear secondary stress, which typically manifests itself as a prominent initial or final syllable (edge-prominence), or as alternation of stressed and unstressed syllables (bounded or alternating stress). An additional factor that often plays a role in stress systems, weight-sensitivity, can be disregarded in Vietnamese, because it has a minimality requirement forcing all syllables to have at least two moras (i.e. it has no light syllables). Furthermore, even researchers who believe Vietnamese has stress agree that it is not contrastive (for full discussion see Section 1.4).

It is important to distinguish stress from phrasal prominence (or phrasal stress), a cover term for a variety of phenomena that can be misinterpreted as stress if words are recorded in isolation or in inadequate frame sentences. Phrasal prominence not only includes the lengthening effects typically found at phrase edges (Beckman & Edwards Reference Beckman, Edwards, Kingston and Beckman1990, Cutler & Butterfield Reference Cutler and Butterfield1990a, Turk & Shattuck-Hufnagel Reference Turk and Shattuck-Hufnagel2000), but can also result from the realization of boundary tones. Along similar lines, stress can be difficult to distinguish from word-final lengthening (Cutler & Butterfield Reference Cutler, Butterfield and Seidl1990b, Byrd Reference Byrd1996, Byrd & Krivokapić Reference Byrd and Krivokapić2006, Fletcher Reference Fletcher, Hardcastle, Laver and Gibbon2010). Information structure (focus, givenness, topicalization) can also affect phrasal prominence, but our understanding of information structure in Vietnamese is still limited (Michaud & Brunelle Reference Michaud, Brunelle, Féry and Ishihara2016).

Word stress (primary or secondary) is phonetically realized by means of a combination of increased duration, intensity and f0, and can also be cued by a reduction of phonological contrast (especially a neutralization of vowel quality) in unstressed syllables (Hayes Reference Hayes1995, van der Hulst Reference Van Der Hulst2012). In a variety of languages a longer syllable duration has been shown to be the clearest acoustic correlate of stress (Fry Reference Fry1955 on English, Sluijter & Van Heuven Reference Sluijter and Heuven1996 and Sluijter, Van Heuven & Pacilly Reference Sluijter, Heuven and Pacilly1997 on Dutch, De Jong & Zawaydeh Reference De Jong and Zawaydeh1999 on Jordanian Arabic, Arvaniti Reference Arvaniti2000 on Greek, Remijsen Reference Remijsen, Gussenhoven and Warner2002 on Ma'ya, Remijsen & Van Heuven Reference Remijsen and Van Heuven2005 on Papamientu, Prieto & Ortega-Llebaria Reference Prieto and Ortega-Llebaria2006 on Spanish and Catalan). The smallest reported stress-conditioned increase in duration is about 10% in word-initial Spanish syllables (Prieto & Ortega-Llebaria Reference Prieto and Ortega-Llebaria2006), but this lengthening is typically much greater in other languages. Note however that durational cues to stress are sometimes less direct. For instance, in Welsh, it is the post-stress consonant that is lengthened, rather than the stressed syllable itself (Williams Reference Williams1985).

Vowel quality and intensity are also generally robust cues, although their exact manifestations and contributions are partly language-specific. In languages that show dramatic reduction or phonological neutralization of vowel contrasts in unstressed syllables, like English, formants are radically centralized. However, even in languages without clear vowel reduction, F1 and F2 are usually affected to some extent (De Jong & Zawaydeh Reference De Jong and Zawaydeh1999, Remijsen Reference Remijsen, Gussenhoven and Warner2002, Remijsen & Van Heuven Reference Remijsen and Van Heuven2005, Prieto & Ortega-Llebaria Reference Prieto and Ortega-Llebaria2006). Formant measurements are difficult to compare across studies, but Jordanian Arabic, with a 5% boost in F1 in stressed syllables seems to have one of the lowest reported differences (De Jong & Zawaydeh Reference De Jong and Zawaydeh1999). The effect of stress on intensity is less straightforward: mean intensity often correlates with stress, but as the energy increase is not equally distributed in the frequency spectrum, a boosted intensity in higher harmonics has been shown to be an even better indicator of stress in Dutch, Spanish and Catalan unaccented syllables (Sluijter & Van Heuven Reference Sluijter and Heuven1996, Sluijter et al. Reference Sluijter, Heuven and Pacilly1997, Prieto & Ortega-Llebaria Reference Prieto and Ortega-Llebaria2006). However, no such effect is found in English (Campbell & Beckman Reference Campbell and Beckman1997), and it seems that, at least in some languages, overall intensity is more correlated with accent (i.e. the association of a melodic target, or pitch-accent, to a stressed syllable) than with stress itself. In fact, it has been proposed that the combined effect of duration and intensity may be a better way of capturing the perceptual prominence of stressed syllables than the two cues taken separately (Beckman Reference Beckman1986, Arvaniti Reference Arvaniti2000). Finally, although f0 is primarily a phonetic correlate of accent, a residual higher f0 may be maintained on stressed syllables, even when unaccented (De Jong & Zawaydeh Reference De Jong and Zawaydeh1999, Remijsen Reference Remijsen, Gussenhoven and Warner2002).

Although they are superficially competing for some of the same acoustic cues, lexical tone and stress are not incompatible in absolute terms. There are many well-described cases of languages where lexical tone and contrative stress coexist (Inkelas & Zec Reference Inkelas and Zec1998 on Serbo-Croatian, Riad Reference Riad1998 and Lahiri, Wetterlin & Jönsson-Steiner Reference Lahiri, Wetterlin and Jönsson-Steiner2005 on Scandinavian, Remijsen Reference Remijsen, Gussenhoven and Warner2002 on Ma'ya, Baart Reference Baart, Baart and Hyder Sindhi2003 on the tonal languages of Pakistan, Remijsen & Van Heuven Reference Remijsen and Van Heuven2005 on Papamientu, Nara Reference Nara2015 on Punjabi). In Ma'ya for instance, stress and tone rely on the same phonetic properties, but weighted in opposite orders (Remijsen Reference Remijsen, Gussenhoven and Warner2002). Perhaps more typically, in many languages with sparse tonal specification as diverse as Swedish (Riad Reference Riad1998, Lahiri et al. Reference Lahiri, Wetterlin and Jönsson-Steiner2005) and Punjabi (Baart Reference Baart, Baart and Hyder Sindhi2003, Nara Reference Nara2015), stress attracts tone and is the primary cue to stressed syllables. On the other hand, we know much less about languages in which tone is densely distributed, especially those in which each syllable has its own lexical stress. In East Asia, the best studied case is Mandarin, a language in which most disyllables have a trochaic structure and where unstressed syllables are segmentally reduced and bear a neutral tone (Norman Reference Norman1988, Chen Reference Chen1993, Duanmu Reference Duanmu2000). Another language where tone and vowel contrasts are neutralized in unstressed syllables is Burmese (Gruber Reference Gruber2011). In the absence of morphophonological alternations, one may wonder if unstressed syllables in these languages still bear an underlying tone, but tonal reduction without full neutralization is also attested: in Thai, unstressed syllables are shorter and have reduced vowels and tones, but tonal contrasts are still maintained (Potisuk, Gandour & Harper Reference Potisuk, Gandour and Harper1994, Reference Potisuk, Gandour and Harper1996). What Mandarin, Burmese and Thai have in common is that word stress is realized through a general reduction of unstressed syllables that includes, but is not limited, to tonal reduction. This contrasts with other East Asian tone languages, like Cantonese (Bauer & Benedict Reference Bauer and Benedict1997) and other southern Chinese languages (Norman Reference Norman1988), that have complex tone systems, but no stress.

Vietnamese is interesting in this context because it has a complex tone system and has often been described as having word stress, but does not exhibit a clear reduction of unstressed syllables in lexical words.Footnote ¹ There is, however, considerable disagreement about the metrical structure of Vietnamese: even native-speaking linguists have failed to reach a consensual description of its stress system (see Section 1.4 for a discussion). The main goal of this paper is therefore to look at Vietnamese in more detail in order to determine if there is any form of word prominence in this language and, if there is any, to conceptually sort out the various forms of prominence at play.

1.2 Vietnamese syllables and tones

There is considerable phonological and phonetic variation between Vietnamese dialects (see Kirby Reference Kirby2011 for a comprehensive phonetic sketch of Hanoi Vietnamese, Brunelle Reference Brunelle, Jenny and Sidwell2015 for phonetic overviews of the northern and southern dialects). However, all dialects share relatively simple phonotactics: all syllables conform to a C(w)V(C) template and bear a lexical tone. Furthermore, there are, to my knowledge, no mentions of dialectal differences in the placement or realization of stress anywhere in the literature. The results presented here are therefore valid for the southern dialect, but should in theory be generalizable to other dialects. For the purpose of this paper, Southern Vietnamese will refer to the relatively homogeneous varieties spoken in Hồ Chí Minh City and the Mekong Delta.Footnote ² There is minor lexical and phonological variation even in that zone, but no salient differences in tone or prosody have been reported. The transcriptions given below correspond to surface forms as pronounced in standard Southern Vietnamese, as it would be spoken in formal contexts by educated native speakers from Hồ Chí Minh City.

Two dialectal features related to tone are relevant to this paper. The first one is that while northern and central varieties have glottalized tones (Nguyễn & Edmondson Reference Nguyễn and Edmondson1997, Phạm Reference Phạm2003, Michaud Reference Michaud2004), southern dialects make no use of voice quality in tonal contrasts (Brunelle Reference Brunelle2009). The second one is that unlike Northern Vietnamese, which has six tones, southern dialects (and many central dialects) have merged the tones C1 (hỏi) and C2 (ngã) and now have a five-tone inventory. This simpler tone system is the reason why this paper focuses on Southern Vietnamese. In citation, the five tones of Southern Vietnamese have the following shapes (Figure 1): tone A1 (ngang) is high-level, tone A2 (huyền) is falling, tone B1 ( sắc ) is rising, tone B2 (nặng) is low falling-rising and tone C (hỏi-ngã) is high falling-rising. Two additional tones are only found in checked syllables (i.e. syllables closed by voiceless stops) and will not be tested here: D1 (checked sắc ) is a rising tone very similar to tone B1 ( sắc ), while D2 (checked nặng) is a falling tone very similar to tone A2 (huyền).

Figure 1 The five tones of Southern Vietnamese in unchecked syllables (mean speaker z-normalized values obtained from all the words pronounced by the 18 speakers recorded for this study).

1.3 The Vietnamese lexicon

The native Vietnamese lexicon is largely composed of monosyllabic roots, but these roots are often compounded into polysyllabic words. Monomorphemic polysyllabic words also exist, but are limited to loanwords and ideophones. Assessments of the prevalence of polysyllables in the Vietnamese lexicon vary: Nguyễn (Reference Nguyễn1997: 35) reports that 80% of the lexicon is composed of disyllables, while Trần & Vallée (Reference Trần, Hiền and Vallée2009: 232) establish the respective proportions of disyllables and trisyllables in a syllabified lexicon at 49% and 1%. The proportion of polysyllables is certainly much lower in spontaneous speech (especially if one looks at token rather than type frequency), but compounds and polysyllables are nonetheless common and well-integrated into the lexicon and phonology. Since the morphosyntactic structure of compounds has been claimed to affect stress, a typological overview of Vietnamese polysyllables is given before addressing the issue of stress proper.

Native Vietnamese compounds can be grouped into two categories: coordinative and subordinative. Coordinative compounds are made up of two roots belonging to the same lexical category, out of which neither can be treated as a syntactic or semantic head. They typically have a generalized meaning which adds up to more than the sum of their parts. Thus, quần áo [wəŋ^A2 ʔaːw ^B1] <pants+shirt> means ‘clothes’. Although most coordinative compounds have a default lexicalized order, this order can be reversed without affecting their core meaning. For instance, áo quần, though much less common and more stylistically marked than quần áo, is acceptable and has the same compositional meaning. Subordinative compounds, on the other hand, are composed of a head and a modifier. As they are rigidly left-headed, they are not reversible. An example is cá heo [ka ^B1 hɛw ^A1] <fish+pig> ‘dolphin’, in which the syntactic and semantic head cá ‘fish’ is modified by heo ‘pig’. Previous researchers have pointed out that there is no clear dividing line between Vietnamese compounds and phrases, be it from phonetic (Ingram & Nguyễn Reference Ingram and Nguyễn2006, Nguyễn & Ingram Reference Nguyễn, Thư and Ingram2007a) or morphosyntactic perspectives (Thomas Reference Thomas1962, Noyer Reference Noyer1998). Frequent compounds seem equivalent to lexicalized phrases.

Reduplicates form a large proportion of the Vietnamese polysyllabic lexicon. One can roughly distinguish three forms of reduplicates. Real reduplicates are formed by applying a productive (or at least common) reduplication template to an existing root (Trương Reference Trương1883, Emeneau Reference Emeneau1951, Thompson Reference Thompson1965). For instance, vui [vuj ^A1] ‘happy’ can be reduplicated into vui vẻ [vui ^A1 vɛ^C] ‘very happy’ and mạnh [man ^B2] ‘strong’ into mạnh mẽ [man ^B2 mɛ^C] ‘very strong’ through a regular rhyme change and a predictable tone alternation.Footnote ³ The few available strategies for creating real reduplicates can result in forms where the base precedes the reduplicant, like in the examples just given, or in forms where the reduplicant precedes the base, as in mành mạnh [man ^A2 man ^B2] ‘strong-ish’. There is also a large set of pseudo-reduplicates, which are reduplicated forms where the reduplicant is lexicalized and cannot be derived from the base through an established morphophonological template. An example is nhút nhát [ɲu ^D1 ɲaːk ^D1] ‘very timid’, which is clearly related to nhát ‘timid’, even if there is no regular u~a reduplication pattern in Vietnamese. To this, one can also add a class of false reduplicates, that are actually a type of adjectival compounds, where an adjective is followed by a verb, like vui thích [vuj ^Á1 tʰɨt ^D1] <happy+to like> ‘very happy’.

There are three other types of polysyllabic words. The first type is ideophones, a large class of words that are phonological similar to reduplicates, but do not share their semantic properties (Brunelle & Lê Reference Brunelle, Lê and Williams2013). Words like lung tung [lu ^A1 tu ^A1] ‘disordered, without a clear goal’, are composed of syllables that share phonological properties, but are not derived through clear morphophonological processes and do not have a base (neither lung nor tung mean anything in isolation). The second type, Sino-Vietnamese compounds, have an ambiguous status as they are often not transparent to native speakers (Alves Reference Alves, Haspelmath and Tadmor2009). This is because Sino-Vietnamese monosyllabic roots are often semantically opaque, just like Latin or Greek roots in Western European languages and because Sino-Vietnamese subordinative compounds are right-headed, contrary to their systematically left-headed native correspondents. For instance, a word like tuần lộc [tuːŋ^A2 lo ^D2] <docile+deer> ‘elk, reindeer’ is opaque because the meaning of its roots is unknown to native speakers (except sinologists and zoologists), while a word like quốc ngữ [wɔk ^D1 ŋɨ^C] <country+language> ‘Vietnamese script’ is probably semantically transparent to all native speakers due the high frequency of its roots, but is structurally marked as its headenedness does not follow the morphosyntactic rules of native Vietnamese. The last type of polysyllabic word is composed of a few hundred monomorphemic polysyllabic loanwords, mostly borrowed from French (ban công [baːŋ^A1 ko ^A1] ‘balcony’ < Fr. balcon; sơ cua [sə^A1 kuə^A1] ‘back-up suitor’ < Fr. roue de secours ‘safety wheel’) (Huỳnh Reference Huỳnh2008), but also from neighboring languages (Sài Gòn [saːj ^A2 ɡɔŋ^A2] name of a city < Khmer pr j nokor Footnote ⁴ ‘City of the forest’, Phan Rang [faːŋ^A1 ɾaːŋ^A1] name of a town < Cham/Sanskrit Panduranga).

This paper focuses on disyllabic words because they are by far the most common type of polysyllables. There is however no theoretical upper limit on the number of syllables in a word. Native coordinative compounds can have more than two syllables (e.g. anh chị em [an ^A1 ci ^B2 ɛm ^A1] <older brother+older sister+younger sibling> ‘siblings’), subordinative compounds/phrases are recursive (nhà máy điện [ɲa ^A2 maːj ^B1 ɗiːŋ^B2] <house+machine+electricity> ‘power station’) and reduplicates can have up to four syllables in some stylistic contexts (Ngô Reference Ngô1984).

1.4 Stress in Vietnamese

To my knowledge, Vietnamese stress has been described in four, largely incompatible, ways. The first is that there is no word stress; as suggested by Emeneau (Reference Emeneau1951: 25), ‘[t]here are no stress phenomena to be noted – every word in connected utterance . . . has the same degree of energy as every other’.Footnote ⁵ The second view is that there is morphosyntactically-defined word stress. This position was first put forward coherently by Cao (Reference Cao2003 [1978]) in a paper in which he made a set of observations about duration and tone reduction in Vietnamese (apparently following observations made in Thompson Reference Thompson1965). Cao did not fully distinguish sentential prominence and word stress, and described processes that seem to go beyond stress, such as phonological reduction of function words and the lexicalization of high-frequency phrases into compounds. However, he did make explicit claims about headeness and stress in coordinative and subordinative compounds, and these were later expanded and formalized by Ngô (Reference Ngô1984: 101). According to Ngô, all lexical words are stressed, but (i) coordinative compounds only have heads and therefore receive stress on each of their syllables, (ii) subordinative compounds receive stress on their non-head, which means that native subordinative compounds should be right-headed while Sino-Vietnamese compounds should be left-headed, (iii) reduplicates receive stress on their base, and (iv) non-Sino-Vietnamese loanwords are stressed on their initial syllable. Ngô’s extension of Cao's proposal to Sino-Vietnamese and non-Sino-Vietnamese loanwords is a radical move, but the general idea that stress is related to headedness remains influential among Vietnamese linguists.

The third position is that Vietnamese stress is always word-final. This is the position adopted by Nguyễn & Ingram, in a series of papers that constitute the only experimental evidence about Vietnamese stress (Nguyễn Reference Nguyễn and Thư2010, Nguyễn & Ingram Reference Nguyễn, Thư and Ingram2007a, Reference Nguyễn, Thư and Ingramb). In a study of disyllabic head-final reduplicates, Nguyễn & Ingram (Reference Nguyễn, Thư and Ingram2007b) found that first syllables are shorter and have more centralized vowels and more reduced f0 contours than second syllables, but that their intensity tends to be stronger; spectral tilt differences independent of tone were not found. Nguyễn & Ingram obtained similar results in a related study of disyllabic coordinative compounds: their second syllable is prominent in terms of F1 and duration, but their first syllable has a stronger intensity unaccompanied by any spectral tilt difference (Nguyễn & Ingram Reference Nguyễn, Thư and Ingram2007a, Figure 5).Footnote ⁶ Based on these results, they proposed that Vietnamese disyllables bear second-syllable stress and conservatively concluded that ‘there was clear acoustic evidence that Vietnamese disyllabic word forms are not symmetrical in terms of accentual prominence, but “right-headed” or biased in weight toward the second element’ (Nguyễn & Ingram Reference Nguyễn, Thư and Ingram2007a: 1757). However, as they acknowledge, the fact that their target words are always phrase-final makes it difficult to determine if second syllable prominence is really due to accentual prominence or if it is a consequence of phrase-final lengthening. In a more recent study, Nguyễn adopted a more formal analysis and proposed, based on an investigation of nonce place names of up to six syllables (e.g. La-na, La-na-ma, La-na-ma-ra, La-na-ma-ra-ga, La-na-ma-ra-ga-nha), that ‘polysyllabic words in Vietnamese tend to be parsed into bi-syllabic iambic feet with a rightward or retrograde [i.e. alternating] rhythmic pattern’ (Nguyễn Reference Nguyễn and Thư2010: 25). Unfortunately, results suggest that the task may have been too awkward to yield natural speech: quadrisyllabic nonce words, which match the longest attested monomorphemic words of Vietnamese (pê ni xi lin [pe ^A1 ni ^A1 si ^A1 lin ^A1] ‘penicillin’, phô tô cóp pi [fo ^A1 to ^A1 kɔp ^D1 pi ^A1] ‘photocopy’), have an abnormally long average duration of about 1200 ms, while hexasyllabic nonce words reach an alarming 2000 ms. Nguyễn's (Reference Nguyễn and Thư2010) claim about the alternating nature of Vietnamese stress thus seems bold, but Nguyễn & Ingram's (Reference Nguyễn, Thư and Ingram2006, Reference Nguyễn, Thư and Ingram2007a, b) more general proposal that stress is word-final or iambic must be considered seriously, especially since it was made independently by other researchers (Trần Reference Trần, Nguyễn, Trần and Dellinger1967, Phạm Reference Phạm2008).

The fourth position is that stress is a phrasal phenomenon. This view was adopted, explicitly or not, by several authors who noticed significant phrase-final lengthening in Vietnamese (Thomas Reference Thomas1962; Thompson Reference Thompson1963, Reference Thompson1965; Hoáng & Hoáng Reference Hoáng and Hoáng1975; Cao Reference Cao2003 [1978]). Some of its proponents deem that this final lengthening is accompanied by recursive iambic phrasal stress (Thomas Reference Thomas1962) or additional morphosyntactic stress (Thompson Reference Thompson1963, Reference Thompson1965; Cao Reference Cao2003 [1978]). A recent version of this proposal has been put forward by Schiering, Bickel & Hildebrandt (Reference Schiering, Bickel and Hildebrandt2010), based on Thompson's (Reference Thompson1965) examples and on a loose reinterpretation of Nguyễn & Ingram's (Reference Nguyễn, Thư and Ingram2006) conclusions. Schiering et al.’s (Reference Schiering, Bickel and Hildebrandt2010) claim is that Vietnamese has neither prosodic word nor word stress, but rather very short phrases (of an undefined nature) with final stress.

In order to determine which of these accounts is the most appropriate, an experimental investigation of Vietnamese stress was conducted. It was designed to determine if there is any form of prominence in Vietnamese disyllables and to assess if such prominence is caused by phrase-final effects or by word stress. Various types of compounds were recorded to see if their morphosyntactic structure affects prominence.