# Rounding contrast activation in Ngbugù: licensing and subsegmental interactions

Galla Althabégoïty, Charles Vancaeyzeele

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## To cite this version:

Galla Althabégoïty, Charles Vancaeyzeele. Rounding contrast activation in Ngbugù: licensing and subsegmental interactions. Radical: A journal of Phonology, In press. hal-04962480

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# Rounding contrast activation in Ngbúgù: licensing and sub-segmental interactions

Althabégoïty, Galla & Charles Vancaeyzeele. 2024. "Rounding contrast activation in Ngbúgù: licensing and sub-segmental interactions". Manuscript available in *Radical: A Journal of Phonology*.

<figure><img src="image_3.png" /></figure>
in South Central Banda, one of the several dialect clusters making up the Banda language
group. The Banda group itself belongs to the hypothetical Ubangi language family, as-
sumed to be part of the Niger-Congo phylum (Cloarec-Heiss 1988, ISO: lnl in glottolog).
To this day, the phonological system of Ngbúgù has been the topic of five publications
(Théret-Kieschke 1998, Boyeldieu and Cloarec-Heiss 2001, Touguele 2008, Althabégoïty
2019, Olson 2022). The present study is based on firsthand data which were collected
from two speakers from the city of Alindao who were living in France at the time of data
collection. The data are consistent with Boyeldieu's (1989, available on RefLex, Segerer
and Flavier 2011) but not with Olson's (2022).

The data show a rounding contrast between [o] and [ɔ] on one hand, between [u] and
[w] on the other. Both contrasts appear to be restricted to seven contexts which all share
a velar component: g_, gв_, k_, кв_ к_, ɲgk_ and ɲk_. For instance, whereas the verbal
forms [gw] ‘to leave, to insult’ and [gu] ‘to grow up, to be far away’ are in opposition,
[tfʷ] and [tʃu] ‘to die’ happen to be in free variation. This contrast is entirely phonologi-
cally conditioned; morphology does not interfere in it whatsoever. Our key proposal is
the following: the rounding contrast is activated in contexts it appears in, rather than neu-
tralized in contexts which lack it. This interpretation is warranted by two empirical facts:
i) the latter contexts greatly outnumber the former and ii) no contrast is attested in onset-
less environments.

The contrast activation is accounted for using the tools of Government Phonology
(Kaye 1990, Kaye *et al.* 1990), Element Theory (Kaye *et al.* 1985, Backley 2011) and
Feature Geometry (Clements 1985, Sagey 1986) suited for elements (Harris & Lindsey
1995, Ulfsbjorninn 2021). Crucially, both velar consonants and back vowels contain an
|U| element, which may also be used to encode rounding (Backley 2011). The overall idea
is that the nucleus may extract elements out of the onset in order to enrich its own matrix.
We stipulate a three-step phonological process. First, the nucleus licenses the preceding
onset. Second, the element matrix of its place node is copied through the application of a
mechanism of ‘SEARCH & COPY’ (Nasukawa 2016). Third, the copied matrix is sent to the place node of the nucleus. If a single |U| element is involved, the nucleic |U| merges with it and becomes head; then the rounding contrast follows. Otherwise the derivation crashes and no rounding contrast is obtainable.

The paper is structured as follows. Section 1 reveals the methodology underlying the collection of the Ngbúgù data and introduces the rounding contrast in more details. Section 2 describes the tools which will help identify the relation between segments at relevant levels of the phonological structure. The account of the Ngbúgù facts is given in section 3.

# 1 THE ROUNDING CONTRAST BETWEEN BACK VOWELS

## 1.1 CONSONANTS AND VOWELS OF NGBÚGÙ

The rounding contrast has been identified in first hand data collected by Althabegoïty (2019) with the assistance of Anicet Ossibouyen Senganambi, a native speaker originating from the city of Alindao (Basse-Kotto, Central African Republic) who resided in France during the enquiry. The data collection was a two-step process. First, a set of basic lexical items from the Greenberg list (to which was added some Tervuren supplement translated and adapted into Gabonese languages by J. Blanchon) were elicited in isolation. Second, once segments were identified, the data were enriched with the manipulation of phonological paradigms, i.e. all possible combinations of consonants and vowels were elicited.

The same data set was used to establish the inventory of Ngbúgù phonemic segments, shown in table (1) and (2). As for consonants, phonemes between parentheses are considered marginal ([r] is only attested in loanwords, and [h] in ideophonic expressions). This inventory quite aligns with that identified by Boyeldieu and Cloarec-Heiss (2001:190) and by Touguele (2008:69). It also slightly differs from Théret-Kiescke’s (1998:32) who proposed a distinct segmental analysis involving affricate sounds.
1) CONSONANT PHONEMES OF NGBÚGÙ

<table><thead><tr><th></th><th>LABIAL</th><th>ALVEOLAR</th><th>PALATAL</th><th>VELAR</th><th>LAB.-VEL.</th><th>GLOTTAL</th></tr></thead><tbody><tr><th>PLOSIVE</th><td>p b</td><td>t d</td><td>ʃ ʃʒ</td><td>k g</td><td>kp ʃb</td><td>ʔ</td></tr><tr><th>FRICATIVE</th><td>f v</td><td>s z</td><td>ʃ ʒ</td><td></td><td></td><td>(h)</td></tr><tr><th>NASAL</th><td>m</td><td>n</td><td>ɲ</td><td>ɲ</td><td></td><td></td></tr><tr><th>LIQUIDS</th><td></td><td>l (r)</td><td>j</td><td>ɲ</td><td>w</td><td></td></tr><tr><th>PRE-NASALIZED</th><td>m b</td><td>n d</td><td>ɲ dʒ</td><td>ɲ</td><td>ɲ</td><td>ɲ</td></tr><tr><th>IMPLOSIVE</th><td>b</td><td>d</td><td></td><td></td><td></td><td></td></tr></tbody></table>

As for vowels, there is a distinction between three degrees of aperture (high, mid and low) and frontness (back, central and front); additionally, a rounding contrast monopolarized by back vowels (boldfaced) is also attested.

2) VOWEL PHONEMES OF NGBÚGÙ

<table><thead><tr><th></th><th>FRONT</th><th>CENTRAL</th><th>BACK</th></tr></thead><tbody><tr><th>HIGH</th><td>i</td><td>i</td><td>w u</td></tr><tr><th>MID</th><td>e</td><td>ə</td><td>ɣ o</td></tr><tr><th>LOW</th><td></td><td>a</td><td></td></tr></tbody></table>

<footnote n="1">¹ One reviewer suggests that we employ the API symbol /ɣ/ (instead of /k/) to represent the velar liquid, which is indeed more phonetically accurate in terms of place of articulation. The use of the /k/ symbol, however, is very well justifiable from a phonological perspective, especially on structuralist accounts (cf. Trubetzkoy 1939). Indeed, the typical realization of /k/ is uvular. So, if we were to add an extra ‘uvular’ column to include it in table 1, we would considerably constrain the proportional oppositions between /k/ and other objects, since no other segment is phonetically uvular. A virtual bilateral opposition between, let’s say, nasals and liquids, would in this case be: $\frac{n}{l} = \frac{n}{j} = \frac{η}{\emptyset} = \frac{\emptyset}{k}$. This relation, logically defective since the last two fractions are lacking either a nominator or denominator value, indicates that uvular /k/ could not be in opposition with nasal segments (as well as /ŋ/ with liquids for that matter). One solution to this problem is to render the relation operational by fusing the ‘velar’ and the ‘uvular’ categories, giving: $\frac{n}{l} = \frac{n}{j} = \frac{η}{k}$. This phonologically more stable series of opposition suggests that /k/ is best considered a phonological velar (even though phonetically uvular). Also, note that /k/ is assigned the same treatment in Boyeldieu and Cloarec-Heiss (2001), for whom uvular and velar realizations altogether form the category of ‘posterior’ consonants.</footnote>
Again, this inventory digresses from previous works in some regards. Touguele (2008), Theret-Kieschke (1998) and Olson (2022) do not acknowledge the [o] vs [ɣ] rounding contrasts, which is instead interpreted as a lowness contrast ([o] vs [ɔ]).<fnref n="2" /> Also, [ɣ] in our data corresponds to [ɔ] in Touguele (2008), Theret-Kieschke (1998) and Olson (2022). The realization of this segment is less rounded and lower than [o]. The choice we made here to represent it as [ɣ] relies on its distribution and the organization of the vocalic system. Because [u] and [u] are in opposition in the same contexts as [ɣ] and [o], we consider that they equally contrast in rounding. An interesting fact to point out is the very limited distribution that afflicts the rounding contrast in back vowels ([u] vs [u] and [o] vs [ɣ]).<fnref n="3" /> We introduce the relevant data in the next section.

**1.2 IDENTIFYING THE ROUNDING CONTRAST**

The analysis we provide of the rounding contrast solely relies on minimal pairs. Before introducing the data, we aim at focusing on the methodology adopted to build the corpus presented in this section.

As an isolating language, Ngbúgù stores numerous monosyllabic morphemes in its lexicon. This peculiarity greatly reduces the probability of finding morphophonologically conditioned allomorphy, as combinatorial possibilities between morphemes are very restrained. In fact, any kind of allomorphic variation is very likely to be free. As a result, an adequate identification of minimal pairs could not be achieved through a simple observation of transcribed wordlists. Chances are, in cases where transcriptions are done

<footnote n="2">² Olson identifies three different mid back vowels ( /ɔ/, /o/ and /ɔ/) whereas we acknowledge only two: /o/ and /ɣ/. First, Every /ɔ/ segment in Olson’s data aligns with /ɣ/ in ours. Second, the minimal pairs which legitimate the /o/ vs /ɔ/ opposition in Olson are interpreted differently in our corpus. Here are a few examples: i) [kpɔtɔ] ‘hat’ contrasts with [kpɔtɔ] ‘skin’ in his, but [kpɔtɔ] is a homophonous form for ‘hat’ and ‘skin’ in ours; ii) the opposition between [kɔ] ‘male’ and [kɔ] ‘type of termite’ in Olson’s corresponds to a tonal alternation for us ([kš] ‘male’ and [kɔ] ‘type of termite’); iii) [dò] ‘divert’ and [tò] ‘marry’ are alternatively transcribed [dɣ] ‘turn’ and [tɣ] ‘marry’, etc.</footnote>

<footnote n="3">³ One reviewer asks if these inconsistencies raising from one transcription to another could be attributed to dialectal variation. Unfortunately, the data we have access to are too limited to answer to this question.</footnote>
before acquiring a sufficient comprehension of the language phonology, the linguist might misinterpret the relation between a surface form and its underlying representation. Consider, for example, the two homophonous morphemes /ŋgú/ ‘water’ and /ŋgú/ ‘year’, both potentially realized [ŋgú] and [ŋgwú].<fnref n="4" /> Problematically, if only the realization [ŋgwú] were registered for ‘year’ and the other realization [ŋgú] for ‘water’, the analyst would most certainly (and incorrectly) hypothesize the existence of a contrast between [u] and [wu].

To reduce the risk of misinterpreting the data, we checked the semantic shift induced by the commutation of one vowel within complete sentences produced by our two Ngbúgù informants. Examples are given in (3). (3a) and (3b) unambiguously reveal a first contrast between the mid back segments [o] and [ɣ], the comparison between (3c) and (3d) indicates a second contrast between their high counterparts [u] and [wu] (alternating back vowels are underlined).

3) a. [ʃè kā là ká-kò máŋgỳ]
3AN.SBJ be with INF-take mango
‘She/he is taking mango.’ [ASEL25_148]

b. [ʃè kā là ká-ky máŋgỳ]
3AN.SBJ be with INF-pick mango
‘She/he is picking mango.’ [ASEL25_149]

c. [mē gú ná]
1SG.SBJ grow_up already
‘I grew up already.’ [AREL13_123]

d. [mē gú ná]
1SG.SBJ leave already
‘I left already.’ [AREL13_118]

This issue now settled, it is important to note that the rounding contrast in back vowels is not systematic. Table (4) shows occurrences of monosyllabic (CV) morphemes in

<footnote n="4">⁴ Ngbúgù has a tonal system, in which three values are attested: low (ù), medium (ū) and high (v).</footnote>
which the contrast either takes place or not<fnref n="5" />. Each row is associated with one place of articulation for the preceding consonant. The two columns distinguish between rounded (left) and unrounded (right) realizations of one back vowel.

4) DISTRIBUTION OF THE ROUNDING CONTRAST IN CV SYLLABLES

<table><thead><tr><th></th><th>ROUNDED VOWELS</th><th>UNROUNDED VOWELS</th></tr></thead><tbody><tr><td rowspan="2">a.</td><td>[ko] (~[kwo]) 'to take'</td><td>[kɔ] 'to pick'</td></tr><tr><td>[ku] (~[kwu]) 'to jump'</td><td>[kwɔ] 'to drip'</td></tr><tr><td rowspan="2">b.</td><td>[ʔo] 'to shout'</td><td>[ʔɔ] 'to shout'</td></tr><tr><td>[ʔu] 'to break'</td><td>N/A</td></tr><tr><td rowspan="2">c.</td><td>[po] 'to talk'</td><td>[pɔ] 'to talk'</td></tr><tr><td>[pu] 'to look for'</td><td>[pwo] 'to look for'</td></tr><tr><td rowspan="2">d.</td><td>[tʃo] 'to taste good'</td><td>[tʃɔ] 'to taste good'</td></tr><tr><td>[tʃu] 'to die'</td><td>[tʃu] 'to die'</td></tr><tr><td rowspan="2">e.</td><td>[to] 'to originate'</td><td>[tɔ] 'to originate'</td></tr><tr><td>[tu] 'ear'</td><td>[twu] 'ear'</td></tr><tr><td>f.</td><td>[kpo] 'to grow up'</td><td>N/A</td></tr></tbody></table>

Interestingly, minimal pairs are identifiable in velar contexts (a), but not in laryngeal (b), labial (c), palatal (d), alveolar (e) and labio-velar (f) contexts.<fnref n="6" /> All of the onsets in table (4) share the same value for voicing (i.e. voiceless) and manner of articulation (i.e. plosive). It appears, then, that only place of articulation can be a conditioning factor for the rounding contrast to occur.

<footnote n="5">⁵ We chose not to represent tones in the examples because they are not relevant for the discussion. In each pair, though, both items contain the same tone as to guarantee the exclusive implication of the alternation in rounding between two semantically different items.</footnote>

<footnote n="6">⁶ The rounded version in velar environments is in free alternation with the realizations [wo] and [wu] (except for nasal velars which systematically exhibit it, as in 4b). For reasons of space, this property is left aside in this paper.</footnote>
Indeed, places of articulation which block the contrast are consistent in their behavior, no matter the specification for voicing and manner of the onset. This is shown in table (5), in which labial (a), palatal (b) and alveolar (c) contexts are enriched with voiced and non-plosive segments.<fnref n="7" /> In any case, no minimal pair is attested.

## 5) NO INTERFERENCE OF VOICING AND MANNER

<table><thead><tr><th></th><th>ROUNDED VOWELS</th><th>UNROUNDED VOWELS</th></tr></thead><tbody><tr><td rowspan="8">a.</td><td>[po] ‘to talk’</td><td>[px] ‘to talk’</td></tr><tr><td>[bo] ‘termite’</td><td>[bx] ‘termite’</td></tr><tr><td>[vo] ‘to pinch by scratching’</td><td>[vx] ‘to pinch by scratching’</td></tr><tr><td>[fo] ‘to rot’</td><td>[fx] ‘to rot’</td></tr><tr><td>[mo] ‘to laugh’</td><td>[mx] ‘to laugh’</td></tr><tr><td>[pu] ‘to look for’</td><td>[pw] ‘to look for’</td></tr><tr><td>[bu] ‘to blacken’</td><td>[bw] ‘to blacken’</td></tr><tr><td>[fu] ‘to be good’</td><td>[fw] ‘to be good’</td></tr><tr><td rowspan="8">b.</td><td>[fɔ] ‘to taste good’</td><td>[fɛ] ‘to taste good’</td></tr><tr><td>[dɔ] ‘to crouch’</td><td>[dɛ] ‘to crouch’</td></tr><tr><td>[tʃu] ‘to die’</td><td>[tʃu] ‘to die’</td></tr><tr><td>[dʒu] ‘back’</td><td>[dʒu] ‘back’</td></tr><tr><td>[ʃu] ‘to be bitter’</td><td>[ʃu] ‘to be bitter’</td></tr><tr><td>[ʒu] ‘to burn (intr.)’</td><td>[ʒu] ‘to burn (intr.)’</td></tr><tr><td>[nʊ] ‘to cook’</td><td>[nʊ] ‘to cook’</td></tr><tr><td>[tɔ] ‘to originate’</td><td>[tɔ] ‘to originate’</td></tr><tr><td rowspan="4">c.</td><td>[do] ‘to turn’</td><td>[dɔ] ‘to turn’</td></tr><tr><td>[tu] ‘ear’</td><td>[tu] ‘ear’</td></tr><tr><td>[du] ‘to age’</td><td>[du] ‘to age’</td></tr></tbody></table>

<footnote n="7">⁷ Table (5) does not include laryngeals nor labio-velars. The former can only be plosive and voiceless in Ngbúgù, and the latter is only instantiated by [k̂p] in our data.</footnote>
The situation is different for velar onsets. More examples of this context are given in table (6). Even though voicing has no influence on the presence of the rounding contrast either (a), manner cannot be so simply discarded. While fricatives favor the contrast (b), no minimal pair is attested in segments with a nasal resonance: nasal (c) and pre-nasalized (d) consonants.

## 6) INTERFERENCE OF MANNER ONLY IN VELAR CONTEXTS

<table><thead><tr><th></th><th>ROUNDED VOWELS</th><th>UNROUNDED VOWELS</th></tr></thead><tbody><tr><td rowspan="4">a.</td><td>[ko] (~[kwo]) 'to give'</td><td>[kɔ] 'to pick'</td></tr><tr><td>[go] (~[gwo]) 'hunger'</td><td>[gɔ] 'territory'</td></tr><tr><td>[ku] (~[kwu]) 'to jump'</td><td>[ku] 'to drip'</td></tr><tr><td>[gu] (~[gwu]) 'to grow up'</td><td>[gw] 'to leave'</td></tr><tr><td>b.</td><td>[ɔo] (~[ɔwo]) 'to take a walk'</td><td>[ɔ] 'to dry'</td></tr><tr><td rowspan="2">c.</td><td>[ŋwo] 'to kill'</td><td>N/A</td></tr><tr><td>[ŋwu] 'to see'</td><td>N/A</td></tr><tr><td rowspan="2">d.</td><td>N/A</td><td>[] 'breast'</td></tr><tr><td>[gɔ] (~[gwu]) 'water'</td><td>N/A</td></tr></tbody></table>

At this point, we can already establish that the rounding contrast cannot be allowed unless two conditions are met: i) the onset is velar; ii) the onset has no nasal component.

Complex onsets add more complexity to the situation. Table (7) exhibits examples whose onsets are composed of a second member [ɔ]. Unsurprisingly, complex velars (a) do allow the rounding contrast, while complex labials (d), alveolars (e), palatals (f) and labio-velars (g) do not. All these contexts remain consistent with that of their simplex configuration. However, complex laryngeals (b) and pre-nasalized velars (c) unexpectedly allow the rounding contrast.<fnref n="8" />

<footnote n="8">⁸ Complex nasals such as *[ŋɔ] or *[mɔ] are not attested in Ngbúgù.</footnote>
7) DISTRIBUTION OF THE ROUNDING CONTRAST IN C_V SYLLABLES

<table><thead><tr><th></th><th>ROUNDED BACK VOWELS</th><th>UNROUNDED BACK VOWELS</th></tr></thead><tbody><tr><td rowspan="2">a.</td><td>[kwo] (~[kwo]) 'to stop'</td><td>[kw] 'to open'</td></tr><tr><td>[gwo] (~[grwo]) 'to touch'</td><td>[gw] 'to sweep'</td></tr><tr><td>b.</td><td>[ʔwo] (~[ʔwo]) 'to whistle'</td><td>[ʔw] 'to scold'</td></tr><tr><td>c.</td><td>[ʔgwo] 'to scratch'</td><td>[ʔgw] 'to make a detour'</td></tr><tr><td rowspan="3">d.</td><td>N/A</td><td>[pw] 'egg'</td></tr><tr><td>N/A</td><td>[fw] 'to rub'</td></tr><tr><td>N/A</td><td>[vw] 'to pour'</td></tr><tr><td rowspan="4">e.</td><td>N/A</td><td>[dw] 'red'</td></tr><tr><td>N/A</td><td>[tw] 'to wipe'</td></tr><tr><td>N/A</td><td>[sw] 'to tear'</td></tr><tr><td>N/A</td><td>[zw] 'to be slippery'</td></tr><tr><td>f.</td><td>N/A</td><td>[ʃw] 'to tighten'</td></tr><tr><td>g.</td><td>[kpu] 'repeatedly'</td><td>N/A</td></tr></tbody></table>

In sum, only seven consonantal contexts allow the rounding contrast between back vowels: ‘oral’ velars k_, g_, ɔ_, kṣ_ and gṣ_, the pre-nasalized velar ʔgṣ_ and the laryngeal ʔk_. Based on these facts, we hypothesize that *the rounding contrast is not ‘neutralized’ in cases it is unattested, but ‘activated’ in cases it is attested.* This interpretation is warranted by the Occam’s razor principle. Stating the condition(s) for the manifestation of a statistically marginal phenomenon (in this case, contrastive rounding) requires less information than stating the condition(s) for its absence. Positing a *contrast activation* will thus unquestionably limit the complexity of the analysis of the Ngbúgù data.

Our proposal is all the more justified that no rounding contrast is attested in onsetless contexts Ø_ either. This can only mean one thing: the contrast is by default inoperative, though rises in case back vowels are inserted in one out of the seven contexts listed above.
The relevant questions regarding the rounding contrast activation are listed in (8). In section 2, we provide the theoretical background that will help answer to those questions.

8) a. Why do ‘oral’ velars activate the rounding contrast?

b. Why do alveolars, palatals, labials and labio-velars block the contrast activation?

c. How can we explain the ambiguous behaviour of simplex vs complex laryngeals and ‘nasal’ velars?

## 2 LICENSING, COPY AND MERGE

In section 1.2, we established that the nature of the onset conditions the rounding contrast activation between back vowels. Interpreting the Ngbúgù facts therefore requires to specify i) the relation between segments and ii) the material they contain. Our theoretical framework, which covers these two aspects, falls within Government Phonology (Kaye 1990, Kaye et al. 1990), Element Theory (Kaye et al. 1985, 1990, Backley 2011) and Feature Geometry suited for elements (Harris & Lindsey 1995, Ulfsbjorninn 2021). The first one is introduced in section 2.1, and the other two in section 2.2. Section 2.3 shows how these tools combine to generate the rounding contrast.

### 2.1 LICENSING AND GOVERNMENT-LICENSING

In Government Phonology (GP), syllabic constituents are bound by relations which condition different aspects of their phonological identity: government and licensing. For instance, onsets (O) require to be licensed by their nucleus (N) to take part in the formation of a syllable (Kaye 1990, Kaye et al. 1990, Charette 1990, 1991, Harris 1994).<fnref n="9" /> This situation is shown in (9a). Similarly, the complement inside a branching<fnref n="10" /> onset (typically instantiated by ‘obstruent + liquid’ sequences) needs the lateral support provided by its

<footnote n="9">⁹ In Kaye (1990) and Kaye *et al.* (1990), this lateral support is provided by government, later re-attributed to licensing by Charette (1990, 1991) and Harris (1994).</footnote>

<footnote n="10">¹⁰ Auto-segments qualify as ‘branching’ if they associate to (at least) two other auto-segments positioned at a lower auto-segmental level.</footnote>
head. In this configuration, illustrated in (9b), the head ($x_1$) governs its complement ($x_2$).<fnref n="11" /> Crucially, head-to-complement government is only possible if the head is licensed by a succeeding N; this is called government-licensing (Charette 1990, 1991).

<figure><img src="image_4.png" /><figcaption>9) a. N-to-O licensing</figcaption></figure>

[t      o]

<figure><img src="image_5.png" /><figcaption>b. Government-licensing</figcaption></figure>

[d      ɔ      ɣ]

Besides binding syllables together, inter-constituent relations also influence the potential of segmental contrasts (Harris 1990, 1994, Cyran 2001, 2010). In Cyran's theory of Complexity Scales and Licensing (CSL), the more segmentally complex a consonant is, the more 'licensing strength' a following nucleus must exhibit. A few examples from Malayalam (borrowed from Cyran 2001:18) are given in table (10). The three rows show consonants with relative segmental complexity:<fnref n="12" /> sonorants (a) are made of two elements, while obstruents (b) have three and 'laryngeally marked' obstruents<fnref n="13" /> (c) potentially even more.

<footnote n="11">¹¹ This type of government is different from Scheer's (2004) 'infra-segmental government'.</footnote>

<footnote n="12">¹² In CSL, segments are represented with elements. The list of elements (non-exhaustive) used by Cyran in table (10) includes: |A| (coronality), |U| (labiality), |N| (nasality), |h| (noise) and |H| (aspiration). These objects are introduced in section 2.2. Note, however, that the set of elements (and their values) used in this paper differs from Cyran's.</footnote>

<footnote n="13">¹³ These are obstruents with extra laryngeal properties, such as voicing and aspiration. Cyran is not explicit about the composition in elements of such segments. He claims, however, that they 'might be a bit more complex than all those followed by schwa' (p. 18), as in row (b).</footnote>
## 10) COMPLEXITY SCALES AND LICENSING

<table><thead><tr><th></th><th>SEGMENT</th><th>ELEMENTS</th><th>LICENSER</th><th>EXAMPLES</th></tr></thead><tbody><tr><td>a.</td><td>[n]<br/>[m]</td><td>(A, N)<br/>(U, N)</td><td>Ø</td><td>[awanØ]<br/>[marjamØ]</td><td>'he'<br/>'tree'</td></tr><tr><td>b.</td><td>[s]</td><td>(A, h, H)</td><td>[ə]</td><td>[kaṭalaasə]</td><td>'paper'</td></tr><tr><td>c.</td><td>[bʰ]<br/>[d]</td><td>≥ 3 elements</td><td>[a]</td><td>[laabʰam]<br/>[maḍam]</td><td>'profit'<br/>'intoxication'</td></tr></tbody></table>

Crucially, consonants which have more than three elements require licensing from a lexically filled nucleus, i.e. [a] in (10c) (e.g. [laabʰam] 'profit'). A nucleus realized with epenthetic schwa, however, may only license consonants with at most three elements, as in (10b) (e.g. [kaṭalaasə] 'paper'). Empty nuclei are even less efficient in this regard: they cannot license consonants which contain more than two elements, as shown in (10a) (e.g. [marjamØ] 'tree'). The Malayalam data therefore strongly indicate that licensing determines the number of segments available at targeted consonantal positions.

## 2.2 THE REPRESENTATION OF NGBÚGÙ SEGMENTS

### 2.2.1 ELEMENT THEORY

Element Theory (ET) manipulates objects called 'elements', which are taken to be the sole primitives of the phonological component. We use Backley's (2011) repertoire, which counts six: three manner elements $|H|$, $|L|$, $|ʔ|$ (approximately corresponding to manner of articulation) and three place elements $|A|$, $|U|$, $|I|$ (approximately corresponding to place of articulation for consonants and quality for vowels). In ET, the substance of each segment in a given language is represented by either one element or a combination of two or more elements.

Starting with vowels, unmarked systems which attest only the five peripheral segments (such as Spanish) will contain the following representations: [a] $|A|$, [i] $|I|$, [u] $|U|$, [e] $|A$
I| and [o] |A U|.<sup>14</sup> In this case, |A| is associated with aperture, |I| with frontness and |U| with backness. Other tools may be required to fully grasp the contrastive potential of segments in more complex systems. One such tool is ‘headedness’, a formal hierarchical property of the relation between elements. This hierarchical relation establishes a distinction between ‘head’ elements and ‘non-head’ elements, the former being more prominent (phonetically and phonologically) than the latter (Harris & Lindsey 1995). Headedness may encode a large array of different contrasts. For example, it has consistently been invoked since Smith (1988) to distinguish ATR segments from non-ATR ones (cf. Charette & Göksel 1986, Harris & Lindsey 1995, Cobb 1997). More recently, Backley (2011) proposed to use headedness as a way of contrasting high-mid with low-mid vowels, among other things.<sup>15</sup>

As we saw in section 1, Ngbúgù has [u] and [x] in its repertoire, which are the un-
rounded versions of [u] and [o] respectively. As a consequence, it is necessary to add a
distinction in rounding inside the representations of high back vowels and mid back vow-
els. Headedness, we believe, is perfectly warranted to achieve this. More precisely, we
claim that non-head |U| is associated with unrounded back vowels [u] and [x], and head
|U| with their rounded counterparts [u] and [o]. In other words, while the |U| element
represents backness, its status as a head represents rounding. This follows naturally from
two considerations. First, rounding is a second property of the |U| element (alongside with
backness). Second, if head elements are indeed more prominent than their non-head
equivalents, then they are expected to carry more phonological information. Table (11)
below shows the representations of the four back vowels of Ngbúgù (the other vowels are
ignored).

<footnote n="14">¹⁴ In some non-standard versions of ET, the |A| element (as well as |H| and |ʔ|) is converted into structure (cf. Pöchtrigger 2006, 2018).</footnote>

<footnote n="15">¹⁵ See Zuk (2022) for a thorough presentation on headedness and its treatment in ET.</footnote>
11) ELEMENTS FOR BACK VOWELS

<table><thead><tr><th></th><th>|U|</th><th>|U|</th></tr></thead><tbody><tr><td>Ø</td><td>w</td><td>u</td></tr><tr><td>|A|</td><td>y</td><td>o</td></tr></tbody></table>

Crucially, we claim that the representations of the four back vowels in table (11) are only valid when they are contrastive in rounding. Recall, however, that this contrast is not systematic (see section 1.2). In this case, the rounded and the unrounded segments in each of both pairs [u]~[w] and [o]~[ɔ] must share the same phonological representation. High and mid back vowels, unspecified for rounding, are thus associated with the underlying segments /U/ and /O/, respectively. These will adopt the same configurations in elements than lexically unrounded /w/ and /ɣ/, i.e. |U| and (U, A). Reasons behind this treatment will become clear in section 3.

As for consonants, most places of articulation are assigned a specific place element, either head or non-head. Again, the following representations are taken from Backley (2011): |U| (velarity), |U| (labiality), |I| (alveolarity) and |I| (palatality). In addition, labiovelars naturally display both |U| and |U|, whereas laryngeal segments have no place element. As demonstrated in section 1.2, manner of articulation has no influence on the rounding contrast of back vowels, except when it comes to velars: while plosives [k], [g] and liquid [ɔ]<fnref n="16" /> allow the rounding contrast, nasal [ŋ] and pre-nasalized [ŋg] do not (see section 1.2). For this reason, only the nasal element |L| is taken into consideration (the manner elements of frication |H| and occlusion |ʔ| are left aside). Table (12) shows the elements of Ngbúgù consonants which are relevant for our purpose.

<footnote n="16">¹⁶ Backley assigns a head |A| to uvular consonants. In our analysis, however, [ɔ] is phonologically velar (see fn. 1).</footnote>
## 12) RELEVANT ELEMENTS FOR CONSONANTS

<table><thead><tr><th></th><th>U</th><th>I</th><th>I</th><th>U</th><th>UU</th><th>Ø</th></tr></thead><tbody><tr><td>...</td><td>p b</td><td>t d</td><td>ʃ ʃʒ</td><td>k g</td><td>k̂p ĝb</td><td>ʔ</td></tr><tr><td>...</td><td>f v</td><td>s z</td><td>ʃ ʒ</td><td></td><td></td><td>(h)</td></tr><tr><td>|L|</td><td>m</td><td>n</td><td>ɲ</td><td>ɲ</td><td></td><td></td></tr><tr><td>...</td><td></td><td>l (r)</td><td>j</td><td>ɲ</td><td>w</td><td></td></tr><tr><td>|L|</td><td>m̂b</td><td>n̂d</td><td>n̂dʒ</td><td>n̂g</td><td>n̂gb</td><td></td></tr><tr><td>...</td><td>b</td><td>d</td><td></td><td></td><td></td><td></td></tr></tbody></table>

## 2.2.2 BARE ELEMENT GEOMETRY

The conception of headedness varies across the literature. The use of underscores to signal head elements, as exemplified in section 2.2.1, is not uncontroversial. In this paper, we follow Ulfsbjorninn's (2021) approach where headedness is thought of as 'structural asymmetry' within expressions.<fnref n="17" /> This approach, called Bare Element Geometry (BEG), stems from the combined principles of ET, Bare Phrase Structure (Chomsky 1993), Dependency Phonology (Anderson & Jones 1974, Anderson & Ewen 1987) and Feature Geometry (Sagey 1986, Clements & Hume 1995).

In BEG, complex element matrices are binary-branching arborescent structures built out of the merging of elements. The representations in (13) offer an illustration of this architecture for each back vowel of Ngbúgù. While the |U| element stands alone in the representation of the high unrounded segment [u] (a), it merges with |A| to generate the mid unrounded segment [x] (b). The representations of the rounded segments [u] (c) and [o] (d) require further clarification. In addition to merging with another element, one element may also merge with another instance of itself; Ulfsbjorninn calls this operation 'self-merge'. The representations in (c) and (d) illustrate this phenomenon. In (d), after

<footnote n="17">¹⁷ Also see the models of Precedence-Free Phonology (Nasukawa 2014, 2016) and GP 2.0 (Pöchtrigger 2006, 2018), where headedness is represented with structure as well.</footnote>
merging with |A|, |U| self-merges and consequently merges with the projection (U, A), yielding the expression (U, (U, A)). In (c), |U| self-merges twice: the first application of self-merge gives the structure (U, U), followed by a second application which results in the expression (U, (U, U)).

13)

a. /u/ |U|

U

c. /u/ (U, (U, U))

<figure><img src="image_6.png" /></figure>

b. /ɪ/ (U, A)

<figure><img src="image_7.png" /></figure>

d. /o/ (U, (U, A))

<figure><img src="image_8.png" /></figure>

The possibility for elements to self-merge allows to distinguish between ‘symmetrical’ expressions (cf. a and b) and ‘asymmetrical’ ones (cf. c and d). Symmetry is to be understood in BEG as a purely geometric property of representations: (c) and (d) are asymmetrical because their shape is different from that of their mirror image (on a vertical axis). In the lines of Dependency Phonology, asymmetry is taken by Ulfsbjorninn to be the true embodiment of headedness. Both structures in (c) and (d) are thus headed by virtue of the fact that (upper) |U| ‘asymmetrically c-commands another instance of itself’ (p. 13). This is why the representation of /u/ (c) requires that |U| self-merges twice. A single application of self-merge would result in the symmetrical configuration (U, U), which lacks asymmetrical c-command. This also means that the two expressions |U| and (U, U) are not contrastive, since i) they are both headless and ii) they contain the same place element. An equally valid representation for symmetrical (U, U) would then be (U, Ø).

The merge mechanism has therefore two functions: i) combining different elements to form complex expressions, and ii) assigning a head to such expressions. This is a major
advantage over ‘non-structural’ approaches to headedness, which rely on the notion of ‘position’ to determine head status in complex expressions (Kaye et al. 1985, Harris & Lindsey 1995, Charette & Göksel 1986, Backley 2011, Faust 2017, among others). That is, there is one position dedicated to the head, and another to the non-head. Problematically, the distribution of these positions is arbitrary; what justifies the assignment of one position to one status (i.e. head or non-head), and why is the other way around excluded (cf. Faust 2017)? In BEG, these questions could not even be formulated, since headedness is defined in purely structural terms.

Element matrices in BEG are also organized in compliance with the architectural principles of Feature Geometry (FG). In that sense, representations such as in (14) are located under hierarchically-organized nodes which altogether shape the substance of segments. Each segment contains three kinds of nodes. Terminal nodes represent functional primes (in this case, elements<fnref n="18" />). ‘Class’ nodes are groupings of those terminal nodes, carrying values such as place, manner or laryngeal resonance. The ‘root’ node corresponds to the segment in its surface form. By combining this architecture with the binary-branching element matrices in (14a) and (14b), we obtain the following representations for unrounded back vowels (skeletal slots above the root nodes are also displayed). The root node put aside, only the place node is required since these segments are exclusively made of place elements (the same goes, of course, for their rounded equivalents).

<footnote n="18">¹⁸ In the standard version of FG (Sagey 1986, Clements & Hume 1995), phonological primes are instanti-
ated by features. The use of elements in this model was introduced by Harris & Lindsey (1995).</footnote>
14)

a. /u/

<figure><img src="image_9.png" /></figure>

b. /x/

<figure><img src="image_10.png" /></figure>

As for consonants, velars and alveolars are associated with symmetrical |U| and |I| respectively, while labials and palatals correspond to asymmetrical (U, (U, U)) and (I, (I, I)). It follows that labio-velars are composed of both asymmetrical (U, (U, U)) and symmetrical |U|. Also, we have to take into account the |L| element inside the representations of nasal and pre-nasalized velar segments. They are given in (15).

15)

a. /ŋ/

<figure><img src="image_11.png" /></figure>

b. /ŋ/

<figure><img src="image_12.png" /></figure>

First, the nasal velar /ŋ/ (a) is made of only one root node, whereas the pre-nasalized velar (b) has two (Piggott 1988, Rosenthall 1989, Ioroi 1995). Second, in both structures, the |L| element is hosted inside a place node. This requires some justification, as in FG the feature [nasal] (or, in this case, its ‘equivalent’ |L|) is generally linked to the root node (cf. McCarthy 1988, Rosenthall 1989, Ioroi 1995, Ulfsbjorninn 2021).<fnref n="19" /> The treatment in

<footnote n="19">¹⁹ In the original version of FG, the feature [nasal] was associated to the ‘supra-laryngeal’ node (Clements 1985, Sagey 1986).</footnote>
(a) and (b) is in fact motivated by empirical evidence. Crucially, the ‘laryngeal’ place of articulation (which bears no place element) is never instantiated by a nasal segment in Ngbúgù. Thus, while non-nasal segments may carry place elements (e.g. /d/, /k/...), never do we find a nasal segment which is not also filled with at least one place element (e.g. ‘nasal’ /ʔ/ or /h/?). We interpret this fact by claiming the existence of a hierarchical dependency between |L| on one hand, {A, I, U} on the other. That is, the former necessarily needs support from at least one place element in order to exist inside the sub-segmental structure.

The two structures in (15) each illustrate one application of this support demanded by |L|. In (a), |U| simply merges with it. Note that this treatment is reminiscent of Harris & Lindsey's (1995) proposition to situate |R|<fnref n="20" /> and place elements under the same 'resonance' (or 'place') node. In (b), however, |U| and |L| may not merge since they belong to two different place nodes. Nonetheless, |L| may maintain itself by virtue of the association line between |U| and Place₁. As a side-effect, the nasal component is also endowed with a velar resonance in its surface form.

## 2.3 THE ‘SEARCH&COPY’ MECHANISM

We saw in section 2.1 that licensing is able to enhance segmental contrasts inside targeted consonantal positions (Harris 1990, 1994, Cyran 2001, 2010). Our proposal to account for the rounding contrast activation between back vowels in Ngbúgù draws from this idea. We hypothesize that licensing may have a beneficial effect, not only for the licensee, but also for the licensor. More precisely, we claim that nuclei may develop additional contrasts through the licensing of preceding onsets.<fnref n="21" /> Under this view, licensing acts as a connection that the nucleus can harness to enrich its own sub-segmental structure.

<footnote n="20">²⁰ The element of ‘coronality’.</footnote>

<footnote n="21">²¹ We thank one of the anonymous reviewers for suggesting the involvement of a licensing relation. They also proposed that we relied on complexity conditions on consonants to derive the activation of contrast, specifically Harris (1994)'s 'Complexity Condition' (CC) and Cyran (2010)'s theory of CSL. It turned out, however, that neither is suitable to the Ngbúgù facts. CC focuses on the interaction between two consonants</footnote>
We submit the application of a three-step phonological process, formally illustrated in (16) ('α' and 'β' designate any element configuration). First, N-to-O licensing occurs (a). Second, the place node of the licensed onset is targeted by the nucleus and its content 'α' is copied (b). This is done through the triggering of a mechanism we label 'SEARCH&COPY' (S&C).<fnref n="22" /> Third, the copied material 'αᵢ' is sent to the place node of the nucleus and merges with its content 'β' (c), according to the principles of BEG (see section 2.2.2).

<figure><img src="image_13.png" /><figcaption>b. S&C (place node)</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>c. Merge</figcaption></figure>

<figure><img src="image_15.png" /></figure>

<footnote>(in a coda-onset sequence or in a branching onset), in that the governor must be less complex than the governor. Nothing is said about the relative complexity of a vowel in terms of licensing relations, except the fact that it may itself be licensed by another vowel which is prosodically more influent at the level of the foot, i.e. which typically bears stress. But it is irrelevant here, since the Ngbúgù data only feature monosyllabic morphemes, so the only nucleus cannot undergo such influence. In CSL, it is assumed that nuclei are distributed on a 'licensing scale' which determines their potential for licensing their onset: lexically filled nuclei are the best licensors, followed successively by alternating nuclei and empty nuclei. Furthermore, structurally less complex onsets are more easily licensable. This unveils an interesting scenario in which the rounding contrast could be developed only if strong licensors and weak licensees were involved. It would immediately collapse, however, when confronted to the data. On one hand, onsets which allow the rounding contrast exhibit extremely various degrees of complexity (cf. ?_ vs ʔgʷ_). On the other hand, nuclei in our data set are all lexically filled, so they could not be discriminated on the basis of their licensing strength. That being said, we do not completely factor out complexity inside the onset. As we will see in section 3, structural complexity for place of articulation is fundamental to account for the data.</footnote>

<footnote n="22">²² Nasukawa (2016) also comes up with a ‘copy’ mechanism in his account of (de-)palatalization in Japanese.</footnote>
In the case of branching onsets, we argue that the nucleus may scope inside both the structure of the head and the complement. Admittedly, it is the head which is licensed by the nucleus, and not its complement. The latter should, therefore, be out of reach of S&C. Recall, however, that a given head is granted the ability to govern its complement specifically because it is licensed (see section 2.1). In other words, the complement owes its existence to the head, which is in turn sustained by the following nucleus. Head-to-complement government can then be viewed as an ‘extension’ of the licensing process. Based on this, we conclude that the nucleus may extend its scope up to the complement. That being said, S&C must target the place node of the head first. Heads take priority over complements since N-to-O licensing occurs before head-to-complement government.

We also posit one more constraint for S&C: it may occur only once. S&C is triggered by licensing, which is itself not a repeatable process. Thus, there is no reason to allow several applications of it. Section 3 is dedicated to the analysis of the Ngbúgù data using the three steps shown in (16).

### 3 (NON-)ACTIVATION OF THE ROUNDING CONTRAST

In the remaining of this paper, we will see how the rounding contrast is activated between back vowels [u] vs [u̯] on one hand, [o] vs [ɔ] on the other. For the sake of conciseness, only representations involving the latter pair are provided.<fnref n="23" /> In particular, we will bring an answer to the three questions below, repeated from (8).

17) a. Why do ‘oral’ velars activate the rounding contrast?

b. Why do alveolars, palatals, labials and labio-velars block the contrast activation?

c. How can we explain the ambiguous behaviour of simplex vs complex laryngeals and ‘nasal’ velars?

<footnote n="23">²³ Also, the [o] vs [ɔ] contrast is attested in more contexts. For instance, the sequences *[ɔu] and *[ɔu̯] are never attested. We cannot precisely figure out why this is the case, but we assume this has to do with a violation of the Obligatory Contour Principle, as both the consonant and the vowel contain an |U| element. But then we should ask ourselves why other velar contexts such as [ku] or [kw] are attested. Perhaps manner elements inside the onset play a part in this. We leave this problem for further investigation.</footnote>
The activation of the rounding contrast in velar contexts (17a) is accounted for in section 3.1. Its failure to take place in alveolar, palatal, labial and labio-velar contexts (17b) is the topic of section 3.2. Finally, sections 3.3 and 3.4 focus on the special case of laryngeal and nasal velar contexts (17c). Recall that these do not trigger the contrast when instantiated by simplex onsets; they do, however, when [k] is selected as a complement.

**3.1 ACTIVATION OF THE ROUNDING CONTRAST: ORAL VELARS**

As observed in section 1.2, the rounding contrast is systematically activated in ‘oral’ velar contexts. In total, five contexts are involved: k_ (e.g. [ko] ‘to give’ vs [kx] ‘to pick’), g_ (e.g. [go] ‘hunger’ vs [gx] ‘territory’), ć_ (e.g. [ćo] ‘to take a walk’ vs [ćx] ‘to dry’), kć_ (e.g. [kćo] ‘to stop’ vs [kćx] ‘to open’) and gć_ (e.g. [gćo] ‘to touch’ vs [gćx] ‘to sweep’).

In (18) are given the representations of underlying /kO/ (a), /ko/ ‘to give’ (b) and /kx/ ‘to pick’ (c). Licensing occurs in the representation of /kO/, in which /O/ is still unspecified for rounding (a). Then, S&C applies and the content |U| under the place node of the onset is copied. It merges with the symmetrical configuration (U, A) inside the nucleus by c-commanding it, yielding asymmetrical (U, (U, A)) (b). This derives rounded /o/. In (c), the newly acquired |U| element is deleted. The structure (Ø (U, A)) being equivalent to (U, A), unrounded /ɣ/ is derived.

It is essential to note that the representations of /o/ and /ɣ/ differ in the outcome of S&C: it is preserved in the former, but not in the latter. This requires some clarification. The concept of contrast activation defended here implies that an unspecified segment, in this case /O/, may acquire extra material to build more contrast, in this case rounding. That being said, we must keep in mind that rounding is contrastive in Ngbúgù especially because rounded and unrounded vowels lexically alternate. It is necessary, then, to allow the deletion of this extra material. This implies that the underlying forms of /O/ and /γ/ are exactly similar. Paradoxically, this does not make these two segments phonologically identical, as merge actually occurred and succeeded in (18c). The cohabitation of these
two possibilities, i.e. the retainment of merge (18b) or its undoing (18c), is what allows
the existence of /o/ and /ʊ/ as distinct phonological objects.

<figure><img src="image_16.png" /><figcaption>b. [ko] /ko/ ‘to give’</figcaption></figure>

<figure><img src="image_17.png" /><figcaption>c. [kʊ] /kʊ/ ‘to pick’</figcaption></figure>

<figure><img src="image_18.png" /></figure>

Representations for the remaining contexts are not given. The analysis of the other simplex contexts g_ and k_ exactly conforms to (18). As for complex k_ and g_, the complement /k/ plays no role here; the structure of the head alone suffices to account for the contrast activation. We will, however, start to acknowledge its significance in section 3.3.
## 3.2 ILLICIT CONFIGURATIONS: LABIALS, ALVEOLARS, PALATALS, LABIO-VELARS

This section focuses on the set of consonantal contexts which never activate the rounding contrast (cf. question 17b). Four places of articulation are concerned, in their simplex as well as their branching form (i.e. which display [ɔ] as a complement): labials (e.g. [po]~[p] ‘to talk’, [vo]~[vɔ] ‘to pinch by scratching’, [pake] ‘egg’, [faka] ‘to rub’), alveolars (e.g. [to]~[tɔ] ‘to originate’, [do]~[dɔ] ‘to turn’, [taka] ‘to wipe’ [saka] ‘to tear’), palatals (e.g. [fɔ]~[tɔ] ‘to taste good’, [faka] ‘to tighten’) and labio-velars (e.g. [kpo] ‘to grow up’, [kpɔ] ‘repeatedly’).

Expectedly, based on the representations in elements of these places of articulation (cf. section 2.2.2), the outcome of S&C (and merge) cannot yield (U, (U, A)) inside the place node of the nucleus. Not only is /o/ impossible to derive in these contexts, but the resulting nucleic structure is actually deficient in either one of the two following ways (or even both): i) it is double-headed; ii) its surface form is not attested in Ngbúgù.

The representations in (19) illustrate these two undesirable outcomes. In labial contexts (a) (e.g. [po]~[pɔ] ‘to talk’), the place node of the onset hosts an asymmetrical (U, (U, Ø)) configuration. During N-to-O licensing, S&C applies and its copied content merges with that of the nucleus (U, A). This yields the expression *(U, (U, A))), where nucleic (U, A) has invested the empty slot Ø of consonantal (U, (U, Ø)). Problematically, the place node of the nucleus ends up with two asymmetrically c-commanding |U| elements: |U|<sub>i</sub> and |U|<sub>j</sub>. In other words, it contains two heads.

In alveolar contexts (b) (e.g. [to]~[tɔ] ‘to originate’), S&C provides the nucleus with an |I| element, which merges with (U, A). The generated configuration *(I, (U, A)) is illicit for two reasons. First, it violates one of the core principles of BEG: the head |I| does not asymmetrically c-command another instance of itself. Second, the simultaneous presence of the three place elements {I, U, A} inside the nucleus cannot be tolerated in Ngbúgù.
The corresponding surface form would be a front rounded vowel, such as [ø], which is
not attested in this language.

19) a. [po]~[pʊ]/pO/ ‘to talk’ (*double-headedness)

<figure><img src="image_19.png" /></figure>

b. [to]~[tʊ]/tO/ ‘to originate’ (*[tə])

<figure><img src="image_20.png" /></figure>

We therefore assume that the consecutive applications of S&C and merge in (19a) and (19b) lead to a derivational crash. Subsequently, the nucleus is unable to develop the rounding contrast; rounded [o] and unrounded [ʊ] remain in free variation. The absence of a contrast activation in palatal and labio-velar contexts goes without saying. Labio-velars are partly labial, so they behave as such (as far as the rounding contrast activation is concerned, at least). As for palatals, they stack up the undesirable properties of both labials and alveolars: the representation of their place of articulation (I, (I, Ø)) is asymmetrical and contains the |I| element.

Finally, branching configurations do not provide the adequate conditions for the round-
ing contrast activation either. Indeed, the place node of the complement [k] cannot be
selected by S&C, as the head must be taken into consideration first.
## 3.3 EMPTY PLACE NODES: LARYNGEALS

How can we explain the divergent behavior of laryngeal onsets? Recall that, while simplex ?_ never allows the rounding contrast to occur (e.g. [ʔo]~[ʔɔ] ‘to shout’) in the succeeding nucleus, its branching equivalent ʔk_ does (e.g. [ʔko] ‘to whistle’ vs [ʔkɔ] ‘to scold’). First and foremost, we established that laryngeals are phonologically unspecified for place of articulation; in other words, they carry no place element. In accordance with the formal mechanisms posited so far, nothing is thus predicted to happen. The lexical structure of laryngeal /ʔ/ has no material inside its place node to be targeted and copied.

The situation is different for branching ʔk_, which displays [k] as a complement. In the previous section, recall that the place node of the complement could not be targeted by S&C. The reason for this was the necessity to check the head in priority. Yet, there is no material inside the place node of laryngeals. S&C may therefore copy the content |U| of the place node of the complement, which merges with the nucleic configuration (U, A). This yields asymmetrical (U, (U, A)), as shown in the representation of [ʔko] ‘to whistle’ (20). The derivation proceeds exactly like in velar contexts (for further details about the contrastive alternation between [o] and [ɔ], see section 3.1).

<figure><img src="image_21.png" /><figcaption>20) [ʔko] /ʔko/ ‘to whistle’</figcaption></figure>
**3.4 THE INTERACTION BETWEEN |L| AND |U|: NASAL AND PRE-NASALIZED VELARS**

Nasal velar contexts exhibit the same hybrid behavior as laryngeals towards back vowels: simplex contexts η_ (e.g. [ŋwo] ‘to kill’) and ηg_ (e.g. [ŋgx] ‘breast’) do not activate the rounding contrast, whereas branching ηgκ_ does (e.g. [ŋgκo] ‘to scratch’ vs [ŋgκx] ‘to make a detour’).

We will first focus on simplex onsets, whose representations are given in (21). As it was established in section 2.2.2, nasal and pre-nasalized velars both have the |L| and |U| elements. The representations of the two segments only differ in the distribution of these elements in their structure. In nasal velars (a), |L| and |U| merge to yield the configuration (L, U) inside a unique place node. In pre-nasalized velars (b), they are scattered across two place nodes (Place₁ and Place₂). Each place node is associated with its own root node (Root₁ and Root₂), and the entire configuration is hosted under one skeletal slot.

<figure><img src="image_22.png" /><figcaption>b. [ŋgx] /ŋgO/ ‘breast’</figcaption></figure>

<figure><img src="image_23.png" /></figure>

In (21a) as in (21b), it is the |L| element which prevents the activation of the rounding contrast. In (a), the (L, U) configuration is copied and merge with nucleic (U, A), yielding the illicit expression *((L, U), (U, A)). The outcome of S&C and merge inside the nucleic structure in (b) asks for further clarification. Two points need to be addressed.
First, the two place nodes inside the onset (Place₁ and Place₂) are simultaneously targeted by S&C. This treatment seems to contradict what we have established so far. Recall that, in all previous contexts containing two place nodes, only one could be selected. However, the situation currently at hand is different. In a branching context, it is impossible for S&C to target both the place node of the head and that of the complement since there is a governing relation that holds between them. The former takes priority over the latter and its structure must therefore be checked first by the nucleus. In (21), even though /্/g/ has two root nodes, the onset is not branching. Thus, there is no head nor complement positions to be distinguished within it; the only lateral relation that holds is licensing. Therefore, the entire structure of /্/g/ is available for checking, and S&C targets whatever place material it can find. Second, |L| and |U| do not merge inside the onset in (21b). Nonetheless, their copy is sent as the merged configuration (L, U) to the nucleus. This is consistent with the idea that S&C is a one-time mechanism. Suggesting that the copies of |L| and |U| were incorporated inside the nucleus as separate objects would entail that S&C actually occurs twice.

In (21a) as in (21b), the reason why the rounding contrast is not activated is quite reminiscent of what happens in (19a) (i.e. labial contexts). The newly born nucleic structure *((L, U), (U, A)) is illicit on formal grounds: it is double-headed. Recall that headedness is defined in BEG as asymmetrical c-command. Since (L, U) asymmetrically c-commands |U| and |A| (located under the (U, A) configuration), both |L| and |U| have head status. Additionally, the expression *((L, U) (U, A)) hosts the |L| element, which is not tolerated inside Ngbúgù nuclei. No nasal vowel is attested in this language. As a consequence, it is impossible for back vowels to develop a rounding contrast in this context.

We will now cover the last remaining context: branching pre-nasalized velars ^n gsk. As was said before, laryngeal and pre-nasalized velar contexts pattern in the exact same way: although simplex onsets do not allow the rounding contrast (cf. ?_ and ^n g_), their branching equivalents do (cf. ?sk_ and ^n gsk_). In section 3.3, we straightforwardly allocated the
divergent behavior of laryngeal contexts to the presence or absence of [v] as a complement. We will shortly see that [v] is also involved in the case of ṛgk_, though in a different fashion. The relevant representation is given in (22).

22) [ṅgkō] /ṅgkō/ ‘to scratch’

<figure><img src="image_24.png" /></figure>

Before discussing the application and the outcome of S&C, a clarification on the formation of the structure of the onset is required. As we can see, there is a (U, U) configuration dominated by both the place node proper to the plosive component of the head /ṅg/ (i.e. Place2) and the single place node of the complement /v/ (i.e. Place3). Here, the two |U| elements which were originally lodged in these place nodes have merged. We legitimate this move by relying on two theoretical principles. First, the Obligatory Contour Principle (Leben 1973), which disfavors the contiguity of two identical objects on the same auto-segmental tier, is satisfied. Second, there is no reason for the phonology to
prevent this operation. According to BEG, (U, U) is indeed equal to |U| in terms of lexical contrast (see section 2.2.2). Velarity is therefore preserved for the entire /্ŋg/ cluster.<fnref n="24" />

Government-licensing occurs and S&C targets both place nodes inside the head x₁ (Place₁ and Place₂), like in (21b). The comparison stops here, however, since the copied material contains the |L| element under Place₁ as well as the above-mentioned (U, U) under Place₂. Both of these elemental configurations then merge to create the virtual *(L, (U, U)) configuration. At this stage, it is essential to point out that this copy of merged elements is structurally ill-formed: |L| does not asymmetrically c-command another instantiation of itself. This does not instantly make the derivation crash, however, since no part of the nucleic structure has yet been affected. Indeed, every crash that occurred in alveolar, palatal, labial and labio-velar contexts was caused by the generation of an illicit configuration of elements inside the nucleus (cf. section 3.2).

If S&C were to send *(L, (U, U)) to the nucleus, another crash would be predicted and the rounding contrast activation would be prevented in this context as well. However, we claim that S&C is unable to proceed further, unless the nucleus is provided with a structurally licit configuration. To achieve this, the problematic |L| element is simply filtered out. Subsequently, only (U, U) is sent for merging. The newly formed configuration under Place₄ is thus ((U, U) (U, A)). Now, considering the fact that (U, U) is lexically equivalent to |U|, the (U, U) configuration indeed asymmetrically c-commands (U, A). The rounding contrast in branching pre-nasalized velar onsets can therefore be activated.

<footnote n="24">²⁴ This merge operation is seemingly identical other principles used in FG, such as Clements' (1985:240) Shared Feature Convention (SFC) and Rosenthall's (1989:68) Inverse Contour Condition (ICC). These are also responsible for the formation of many-to-one relations between auto-segments. We do not claim, nevertheless, that the merged (U, U) configuration in (22) is the outcome of either of these. SFC and ICC were posited to account for assimilation processes, such as gemination and nasal-plosive homorganicity. They are thus irrelevant to the present study.</footnote>
## CONCLUSION

In this paper, we have provided an explanation for the contextual rounding contrast between the two pairs of back vowels [o] vs [ɔ] and [u] vs [ʊ] in Ngbúgù. This contrast is only attested in seven consonantal contexts: k_, g_, ɔ_, kɔ_, gɔ_ ɔk_ and ɒgɔ_, thereby warranting the hypothesis of a *contrast activation* (rather than a *contrast neutralization*). Crucially, the presence of a velar component is a necessary condition for the activation of this contrast. Labial, alveolar, palatal and labio-velar contexts never allow it. However, while simplex laryngeals (?_), nasal and pre-nasalized velars (ŋ_, ɒg_) forbid the contrast as well, their branching configuration ɔk_ and ɒgɔ_ do not.

Relying on the frameworks of GP, ET and FG, we suggested the consecutive application of three mechanisms: i) N-to-O licensing (as well as government-licensing, in case of branching onsets); ii) S&C, a scoping mechanism that allows the nucleus to search and copy the material inside the place node of its licensee; iii) the merging of the elemental configuration in the nucleus with this copied material, through which its contrastive power may be enhanced. We attempted to answer to three questions, listed below (repeated from 8).

23) a. Why do ‘oral’ velars activate the rounding contrast?

b. Why do alveolars, palatals, labials and labio-velars block the contrast activation?

c. How can we explain the ambiguous behaviour of simplex vs complex laryngeals and ‘nasal’ velars?

‘Oral’ velars activate the rounding contrast (cf. question 23a) because the place node of the onset contains a unique |U| element. Once |U| merges with the place configurations |U| or (U, A) inside the nucleus, a new asymmetrical (i.e. headed) configuration (U, (U, U)) or (U, (U, A)) is generated. This derives rounded vowels /u/ and /o/, respectively. The formation of their lexically unrounded equivalent /u/ and /ɔ/ is then achieved by the deletion of the asymmetrically c-commanding element inside the nucleus.
However, alveolar, palatal, labial and labio-velar contexts may not activate the round-
ing contrast (cf. question 23b) since the content of their place node is inadequate. When
the latter merges with that of the nucleus, an illicit configuration is generated. The deri-
vation then crashes, and the following back vowel /U/ or /O/ remains unspecified for
rounding. Also, when the onset is branching, the nucleus cannot exploit the velar comple-
ment /k/; the place node of the head must be targeted in priority.

The answer to question (23c) is twofold. The place node of laryngeal segments is empty, so no material can be extracted out of it by S&C. When the laryngeal onset is branching, however, the |U| element of its complement /k/ may be targeted by S&C. As for simplex ‘nasal’ velars, the integration of their |L| element inside the nucleic structure generates once more an illicit configuration. When they are in a branching configuration, however, the |U| element inside the complement disables it for structural reasons.

Further work will have to investigate other interesting vocalic distributions occurring
in Ngbúgù. We introduce two of them. First, other data we collected suggest that the con-
trast between front and central vowels is also absent in some contexts. For example, [i]
and [ə] never appear after a labial or a palatal consonant. Similarly, [i] is rarely attested
in alveolar contexts. Second, the rounded back vowels [u] and [o] might freely alternate
with a diphtonguized equivalent ([wo] and [wu]), but only in velar and branching laryn-
geal contexts.

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ABSTRACT IN FRENCH

La langue ngbúgù (banda, Ubangi, RCA) manifeste un contraste con-
textuel entre voyelles arrondies et non-arrondies ; les deux contrastes
[o] vs. [ɔ] et [u] vs. [ʊ] ne sont productifs que dans quatre contextes :
i) K(ɔ)_ , ii) ɔ_, iii) ɔ?_ et iv) ɔ'gɔ_ (où K représente à la fois /k/ et /g/).
Étant donné la distribution limitée de ce contraste, nous proposons qu'il
soit activé dans ces contextes, plutôt que neutralisé ailleurs. En nous
situant dans le cadre de la Théorie des Éléments (Kaye et al. 1985, 1990,
Ulfsbjorninn 2021, parmi d'autres) et de la Phonologie du Gouverne-
ment (...), nous proposons une approche représentationnelle dans la-
quelle l'élément |U| est responsable de cette activation.