# Variation in the coding of the noncausal/causal alternation:
Causative *-i in East Bantu languages

Sebastian Dom
University of Gothenburg

Leora Bar-el
University of Montana

Ponsiano Sawaka Kanijo
Mkwawa University College of Education

Malin Petzell
University of Gothenburg

## ABSTRACT

In this paper, we discuss shifts in the formal relation, i.e. “correspondence” (Haspelmath 1993; Nichols et al. 2004), between members of noncausal/causal verb pairs in eight East Bantu languages. These shifts are the effect of diachronic changes to the morphophonological structure of the verbs involved, conditioned by reflexes of a reconstructed Proto-Bantu causative suffix *-i*. In the history of many Bantu languages, the high vowels *i* and *u* conditioned a series of sound changes on the preceding consonant. The suffixing of the causative suffix *-i* to a verb root is one context in which these sound changes occurred. We investigate noncausal/causal pairs in eight East Bantu languages in which the causal verb is historically derived by a reflex of the suffix *-i*. We argue that many of these noncausal/causal pairs changed from a causative to another correspondence. Our analysis has implications for the study of the formal alternations of noncausal/causal verb pairs across all Bantu languages and beyond.

## KEYWORDS

causative, correspondence types, East Bantu, noncausal/causal alternation

## RÉSUMÉ

Dans cet article, nous traitons des changements dans la relation formelle, c'est-à-dire la « correspondance » (Haspelmath 1993; Nichols et al. 2004), entre les membres de paires de verbes non causals/causals dans huit langues bantoues orientales. Ces décalages sont causés par les changements diachroniques de la structure morphophonologique des verbes concernés, conditionnés par les réflexes d'un suffixe causatif *-i* proto-bantou reconstruit. Dans l'histoire de nombreuses langues bantoues, les voyelles hautes *i* et *u* ont conditionné une série de changements sur la consonne qui précède. La suffixation du marqueur causatif *-i* à la racine d'un verbe est l'un des contextes dans lequel ces changements phonétiques se sont produits. Nous étudions les paires non causals/causals dans huit langues bantoues orientales dans lesquelles le verbe causal est historiquement dérivé par un réflexe du suffixe *-i*. Nous soutenons qu'un grand nombre de ces paires non causals/causals ont changé d'une correspondance causale à une autre. Notre analyse a des implications pour l'étude des alternances formelles des paires de verbes non causals/causals dans toutes les langues bantoues et au-delà.
# MOTS CLÉS

alternance noncausal/causal, bantou oriental, causatif, types de correspondance

## 1. INTRODUCTION

Verbal affixation is the most common strategy in Bantu languages for coding valency alternations. For example, causative voice in Ngoni ([xŋi]; N12)<fnref n="1" /> is coded by the suffix -is, as illustrated in (1).

(1) Ngoni (Ngonyani 2003: 67)

<table><tr><td>a.</td><td>Niheka.</td><td>b.</td><td>Akunihekesa.</td></tr><tr><td></td><td>ni-hek-a</td><td></td><td>a-ku-ni-hek-is-a</td></tr><tr><td></td><td>SBJ.1SG-laugh-FV</td><td></td><td>SBJ.3SG.1-PRS-OBJ.1SG-laugh-CAUS-FV</td></tr><tr><td></td><td>'I am laughing.'</td><td></td><td>'S/he is making me laugh.'</td></tr></table>

Formally different causative suffixes are attested across Bantu languages (Bastin 1986), and many Bantu languages have two or more formally different causative suffixes. For example, Ruruuli-Lunyala ([ruc]; JE103) has two, namely -esy (2a) and -y (2b).

(2) Ruruuli-Lunyala (Namyalo et al. 2021: 70-71)

a. bon-esy-a<fnref n="2" /> ‘cause to see, show’ < bon-a ‘see’

b. gonger-y-a ‘annoy, upset so.’ < gonger-a ‘be annoyed, upset’

Bostoen & Guérois (forthcoming) reconstruct four causative suffixes, *-i, *-ic, *-idi and *-iki.<fnref n="3" /> In this paper, we focus on causative verbs derived by reflexes of the vocalic causative suffix *-i. Overt reflexes or morphophonological traces of the Proto-Bantu (henceforth, PB) causative suffix *-i are attested throughout most of the Bantu languages (see Bastin 1986: 131-140).<fnref n="4" /> We examine morphophonological changes conditioned by reflexes of this suffix in several East Bantu languages. We argue that these morphophonological changes affect the formal relation between members of a noncausal/causal verb pair, i.e. their “correspondence” (Haspelmath 1993; Nichols et al. 2004). We show that several verb pairs in causative correspondence in earlier stages of the languages are now in ablaut, partial suppletive or equipollent correspondence. In doing so, we raise an important question about the role of morphophonological developments in identifying correspondence types of noncausal/causal verb pairs. Morphophonological changes of causativized verbs historically derived by reflexes of the PB suffix *-i are attested throughout Bantu (see Bastin 1986: 131-140). Thus, this discussion has implications for a wider range of Bantu languages.

The languages under discussion in this paper are Ikoma ([ntk]; JE45), Matengo ([mgv]; N31), Standard Swahili<fnref n="5" /> ([swh]; G42a), Kagulu ([kki]; G12), Kwere ([cwe]; G32), Zaramo ([zaj]; G33), Luguru ([ruf]; G35), and Kutu ([kdc]; G37). These languages are surveyed because comparative datasets of noncausal/causal verb pairs, based on the wordlist by Haspelmath (1993: 97), are available for all

<footnote n="1">1. Language names are followed by their ISO 639-3 code and Guthrie code (Hammarström 2019).</footnote>

<footnote n="2">2. Synchronic verb forms are presented as *ROOT-a*, where the suffix -a is a “default” suffix found in most Bantu languages, and commonly referred to as “final vowel” (FV) in Bantu linguistics (Nurse 2008: 261). We label the suffix as “default” because -a typically appears in a semantically heterogeneous group of constructions throughout Bantu, in contrast to other tense-aspect-mood suffixes which have a narrower and semantically more specified distribution (for a brief discussion, see Nurse 2008: 261).</footnote>

<footnote n="3">3. The first three, *-i, *-ic and *-idi are reconstructed to Proto-Bantu, the most recent common ancestor of all Bantu languages, while the fourth causative suffix, *-iki, was innovated at a later stage.</footnote>

<footnote n="4">4. The exception seems to be those languages belonging to zone R in the Guthrie classification (Bastin 1986: 106). However, reflexes of this causative do appear in Yeyi (R41) (Seidel 2008: 240-241). We thank Hilde Gunnink for bringing this to our attention.</footnote>

<footnote n="5">5. We use “Swahili” throughout the paper to refer to the Standard variety of the language.</footnote>
eight.<fnref n="6" /> Kagulu, Kutu, Kwere, Luguru and Zaramo constitute a genealogical cluster together with Kami (Petzell & Hammarström 2013), which we call “Greater East Ruvu”. Kami is not considered in this paper since we have not yet collected data on the language, primarily due to the pandemic. All eight languages belong to East Bantu, a major subgroup of the Bantu languages (Grollemund et al. 2015).

The rest of the paper is organized as follows. In Section 2, we present an overview of the non-causal/causal alternation and the typology of correspondence types. In Section 3, we demonstrate how reflexes of the PB causative suffix *-i have been impacted by morphophonological changes in Bantu languages. In Section 4, we examine the effect of these changes on the correspondence types of noncausal/causal verbs pairs. Finally, we conclude in Section 5 with a discussion of the importance of typological studies of this kind as well as the implications of our analysis for understanding basic valence orientation cross-linguistically.

## 2. THE NONCAUSAL/CAUSAL ALTERNATION AND THE TYPOLOGY OF CORRESPONDENCE TYPES

The noncausal/causal alternation refers to pairs of semantically related predicates that denote the same core event but differ in semantic causativity (for an in-depth discussion, see Introduction, this issue). Cross-linguistically, we observe variation in the formal relation between the members of an alternating noncausal/causal pair. For example, in the English verb pair *boil* (intr.)/*boil* (tr.), the non-causal meaning and its causal counterpart are expressed by the same form *boil*. In Herero ([her]; R31A), the noncausal verb *sum-a* ‘boil (intr.)’ and the causal verb *sum-is-a* ‘boil (tr.)’ share the same root *sum*. However, the noncausal verb has no derivational suffix, while the causal verb is derived by adding the causative suffix *-is*.

Haspelmath (1993) and Nichols et al. (2004) explore the cross-linguistic variation in formal relations of noncausal/causal verb pairs. The different formal relations group into correspondence types (Nichols et al. 2004: 152). Table 1 summarizes the correspondence types proposed in Haspelmath (1993: 90-92) and Nichols et al. (2004: 159), presented in alphabetic order.

<table><caption>Table 1 — Cross-linguistic correspondence types (Haspelmath 1993; Nichols et al. 2004)</caption><thead><tr><th></th><th></th></tr></thead><tbody><tr><td>Ablaut</td><td>There is a difference in vowel or consonant quality between the noncausal and causal stems, but the predicates are not formally derived through a (de)transitivization process.</td></tr><tr><td>Adjective</td><td>The noncausal meaning is denoted by an adjective, the causal meaning by a verb.</td></tr><tr><td>Anticausative (aka reduced)</td><td>The noncausal predicate is formally derived through a detransitivization process that is absent in the causal predicate.</td></tr><tr><td>Auxiliary change</td><td>The noncausal member takes a different auxiliary or light verb than the causal member.</td></tr><tr><td>Causative (aka augmented)</td><td>The causal predicate is formally derived through a transitivization process that is absent in the noncausal predicate.</td></tr><tr><td>Conjugation class change</td><td>The noncausal member takes a different conjugation class than the causal member.</td></tr><tr><td>Equipollent (aka double derivation)</td><td>Both members are formally derived.</td></tr><tr><td>Labile (aka ambitransitive)</td><td>A single form is used to denote both the noncausal and causal meaning.</td></tr><tr><td>Suppletion</td><td>The noncausal and causal members have different, i.e. non-cognate, roots. Pairs are partially suppletive when the roots “are partly cognate but not related by any direct morphological process” (Nichols et al. 2004: 159).</td></tr></tbody></table>

<footnote n="6">⁶ Data from Kagulu, Kwere, Zaramo, Luguru and Kutu were collected as part of a research project on valency-decreasing alternations in Greater East Ruvu Bantu languages, funded by the Swedish Research Council (Grant number 2019-02880).</footnote>
The correspondence type of the aforementioned English verb pair *boil* (intr.)/*boil* (tr.) is labile as a single form *boil* is used for both noncausal and causal meanings. The correspondence type of the Herero noncausal/causal pair is causative as the addition of the suffix *-is* derives the causal meaning, which is absent from the noncausal form.

Previous studies (Haspelmath 1993: 118-119; Yoneda 2014a; 2014b; 2014c; 2014d) identify five correspondence types from Table 1 in a selection of Bantu languages, illustrated in (3) with examples from Herero ([her]; R31A) in (3).

(3) Herero (Yoneda 2014a)

<table><thead><tr><th>Correspondence type</th><th>Noncausal</th><th>Causal</th></tr></thead><tbody><tr><td>a. Anticausative</td><td><i>han-ik-a</i> ‘split (intr.)’</td><td><i>han-a</i> ‘split (tr.)’</td></tr><tr><td>b. Causative</td><td><i>sum-a</i> ‘boil (intr.)’</td><td><i>sum-is-a</i> ‘boil (tr.)’</td></tr><tr><td>c. Equipollent</td><td><i>pend-uk-a</i> ‘wake up (intr.)’</td><td><i>pend-ur-a</i> ‘wake up (tr.)’</td></tr><tr><td>d. Labile</td><td><i>pat-a</i> ‘close (intr.)’</td><td><i>pat-a</i> ‘close (tr.)’</td></tr><tr><td>e. Suppletive</td><td><i>yaand-a</i> ‘finish (intr.)’</td><td><i>man-a</i> ‘finish (tr.)’</td></tr></tbody></table>

In this paper, we focus on noncausal/causal verb pairs in which the causal verb is historically derived with a reflex of the PB causative suffix *-i.

3. SOUND CHANGES INVOLVING REFLEXES OF PROTO-BANTU CAUSATIVE *-i

While most Bantu languages have a five-vowel system, Proto-Bantu is reconstructed with a seven-vowel system, /i, ɪ, ε, u, ō, a/. The reconstructed system has an opposition between tense and lax high vowels *i/*i and *u/*ʊ (Hyman 2019: 128-131). Nearly all Bantu languages reduced the seven-vowel inventory to a five-vowel system. Those languages, as well as a small number of languages that retained a seven-vowel system, participated in a sound change where stops became fricatives before reflexes of the Proto-Bantu high tense vowels *i and *u (Schadeberg 1994; Hyman 2003a: 53-55; Bostoen 2008: 310-311).<fnref n="7" /> This change is illustrated in (4), where the stop /d/ in the Proto-Bantu words has become the fricative /z/ in Nyamwezi when followed by the tense high vowels *i and *u.

(4) Proto-Bantu Nyamwezi ([nym]; F22) (Bostoen 2008: 305)

a. *dīm ‘to extinguish’ zim ‘to extinguish’

b. *dùb ‘to fish’ zuβ ‘to fish’

There are five contexts in which a consonant was historically followed by a tense high vowel *i or *u, illustrated in examples (4)-(8) (relevant phonemes are bolded): morpheme-internally (4); when a verb stem is derived with a reflex of the Proto-Bantu nominal suffix *-i to form an agentive nominal stem (5); when a verb stem is derived with a reflex of the Proto-Bantu suffix *-u to form an adjectival stem (6); when a verb stem is derived with a reflex of the Proto-Bantu causative suffix *-i to form a causative verb stem (7); and when a verb stem is inflected with a reflex of the Proto-Bantu suffix *-ide (8).

(5) Tabwa ([tap]; M41) (Bostoen 2008: 300)

end-a ‘travel’ > mu-enz-‘traveller’

(6) Kinga ([zga]; G65) (Labroussi 1999: 344)

yolok-a ‘be(come) straight’ > yolos-u ‘straight’

<footnote n="7">7. In five-vowel languages, the distinction between the high tense and lax vowels has become obscure. The vowel /i/ in these present-day languages can be the reflex of Proto-Bantu *i, historically inducing frication on the preceding consonant, or it can be the reflex of Proto-Bantu *i, which did not trigger frication.</footnote>
(7) Nyakyusa ([nyy]; M31) (Persohn 2017: 85)
*pyu>p-a* ‘get warm’ > *pyu>f-y-a*<fnref n="8" /> ‘warm, heat up’

(8) Nyamwanga ([mwn]; M20) (Labroussi 1999: 348)
*wo>l-a* ‘rot’ > *zjawoz-ile* ‘they rotted’

The frication induced by (reflexes of) high vowels is no longer a productive sound change. Synchron-
ically, then, the diachronic sound change is typically observable as a morphophonological alternation
between stops and fricatives, as can be seen in (4)-(8).

The most widely attested outcome of the sound changes is the lenition of consonants into bilabial, labio-dental, alveolar or post-alveolar affricates or fricatives, as shown in (4)-(8). This sound change is often referred to as “spirantization” (Schadeberg 1994; Labroussi 1999) or “Bantu Spirantization” (Schadeberg 2003; Janson 2007; Bostoen 2008; 2019). In some Bantu languages, spirantization has led to devoicing and weakening, culminating in the loss of the consonant entirely (Hinnebusch 1981: 37; Janson 2007: 88). The stages for this development are serialized by Hinnebusch (1981: 38) shown in (9).

(9) PB: *p, t, k, B, l, G/\_High Vowel
Stage 1: Spirantization yields /f, s, v, z/
Stage 2: Spirant-devoicing yields /f, s/
Stage 3: Spirant-weakening yields /h/
Stage 4: /h/ > Ø

The Ndengeleko ([ndg]; P11) example in (10) illustrates the final stage: the nasal-consonant cluster /nd/ of the verb root *téénd* ‘do, act’ is no longer realized in the past/perfect form *teé-i*, where the root is followed by the suffix -i, a reflex of Proto-Bantu *-ide*.

(10) Ndengeleko (Ström 2013: 84)
*téénd-a* ‘do, act’ > *téé-i*

In this paper, we focus on sound changes that involve reflexes of the PB causative suffix *-i* in noncausal/causal verb pairs. Depending on a language’s diachronic morphophonology, verb stems derived by the PB causative *-i* could have undergone (a) spirantization and, subsequently, (b) loss of the causative suffix when preceded by a fricative or affricate. The second effect is called “absorption” in the literature (Bastin 1986: 131; Hyman 2003b: 81-87; Bostoen 2008: 313-314): the causative suffix, realized typically as a glide /y/ due to vowel hiatus resolution with a following vowel, is absorbed by the fricated consonant. A hypothetical sequence of these sound changes is given in (11). The relevant phonemes for each change are bolded.

(11) Hypothetical serialization of spirantization and absorption for the sequence */t-i-a/ (Hyman 2003b: 82)

*\*t-i-a > *\*t-y-a > *\*s-y-a > s-a

glide formation spirantization absorption

The attested variation of verb stems derived with reflexes of PB *-i* according to spirantization and absorption is illustrated for six Bantu languages in (12)-(16). Examples (12)-(13) illustrate languages

<footnote n="8">8. Reflexes of the PB causative suffix *-i* are typically followed by a vowel of another verbal suffix, and they become real-
ized as /y/ as a result of vowel hiatus resolution. The greater constriction of the glide, as opposed to a vowel, enhances the
frication effect already induced by the high vowel /i/ (Bastin 1983: 25; Hyman 2003b: 58; Bostoen 2008: 314).</footnote>
that have retained the reflex of the PB causative suffix *-i* and in which there is either no change in the stem-final consonant (12), or frication of the stem-final consonant (13).

(12) Ruruuli-Lunyala ([ruc]; JE103) (Namyalo et al. 2021: 71)

<table><tr><td>Noncausal</td><td>Causal</td></tr><tr><td><i>naab-a</i> ‘wash (intr.), get washed’</td><td><i>naab-y-a</i> ‘wash (tr.), cause to get washed’</td></tr></table>

(13) Sumbwa ([suw]; F23) (Kahigi 1988: 104)

<table><tr><td>Noncausal</td><td>Causal</td></tr><tr><td><i>puup-a</i> ‘be(come) light (not heavy)’</td><td><i>puuf-y-a</i> ‘make light (tr.)’</td></tr></table>

Examples (14)-(16) illustrate languages in which sound changes have resulted in the boundary between the stem and the reflex of suffix *-i* no longer being segmentable. In Fwe ([fwe]; K402), the reflex of the causative suffix *-i* triggered frication of the stem-final consonant, and subsequently the glide became absorbed, shown in (14).

(14) Fwe (Gunnink 2018: 210)

<table><tr><td>Noncausal</td><td>Causal</td></tr><tr><td><i>boor-a</i> ‘come back’</td><td><i>booz-a</i> ‘bring back’ (<i>*boor-y-a</i>)</td></tr></table>

In Matuumbi ([mgw]; P13), the lenition process led to the loss of the stem-final consonant, while the reflex of causative *-i* is retained, illustrated in (15).

(15) Matuumbi (Odden 2003: 538)

<table><tr><td>Noncausal</td><td>Causal</td></tr><tr><td><i>bol-a</i> ‘be(come) rotten’</td><td><i>bo-y-a</i> ‘let rot (tr.)’ (<i>*bol-y-a</i>)</td></tr></table>

In Matengo ([mgv]; N31), both the stem-final consonant and the causative suffix were lost. This is shown in (16).

(16) Matengo (Nobuko Yoneda p.c.)

<table><tr><td>Noncausal</td><td>Causal</td></tr><tr><td><i>book-a</i> ‘move (intr.)’</td><td><i>boo-a</i> ‘move (tr.)’ (<i>*book-y-a</i>)</td></tr></table>

In Fwe, Matuumbi and Matengo, the coding of causativization has shifted from the derivational suffix *-i* to apophony, that is, the mutation of the stem-final consonant.<fnref n="9" /> Because of this development, the causative verbs that are historically derived by reflexes of the PB suffix *-i* are no longer part of the derivational paradigm. Instead, the verbs have become reanalyzed as independent, underived lexemes that need to be learned individually and separately from the derivational word-formation processes. The coding strategy for causativization through suffixation by *-i* has been replaced by other causative suffixes or other strategies. The apophony alternation is not generally recognized as a productive coding strategy for causativization in these languages. This lack of productivity is most likely a result of the tendency of Bantu languages to code voice alternations through derivational suffixes.

<footnote n="9">⁹ Typically, apophony is not the only coding strategy for causative meaning in these languages. One or more reflexes of the other causative suffixes reconstructed to PB have been retained (Section 1). Alternatively, another strategy might have been innovated such as, for example, an auxiliary construction.</footnote>
## 4. NONCAUSAL/CAUSAL VERB PAIRS WITH REFLEXES OF THE CAUSATIVE SUFFIX *-i

In this section, we examine the correspondence types of noncausal/causal verb pairs involving reflexes of PB *-i in eight East Bantu languages. The comparative data are based on Haspelmath's (1993) word list and Dom et al.'s (2021) sentence questionnaire. Data from Ikoma, Swahili and Matengo are reproduced here from Laine et al. (this issue), Yoneda (2014c) and Yoneda (2014b), respectively. Data from the five Greater East Ruvu languages Kagulu, Kutu, Kwere, Luguru and Zaramo were collected via fieldwork (for detailed studies on Kagulu and Luguru, see Dom et al. forthcoming a and b). We show that causative noncausal/causal verb pairs derived by the PB causative suffix *-i are attested in Ikoma and Swahili (Section 4.1). We argue that Swahili and the Greater East Ruvu languages have verb pairs historically derived by the PB causative suffix *-i that should be categorized as being in ablaut correspondence (Section 4.2); Matengo has verb pairs historically derived by the PB causative suffix *-i that should be categorized as being in partial suppletive correspondence (Section 4.3); and, finally, we propose that all eight East Bantu languages under investigation in this paper have verb pairs historically derived by the PB causative suffix *-i that should be categorized as being in equipollent correspondence (Section 4.4).

### 4.1 Verb pairs in causative correspondence

Ikoma has preserved the PB causative suffix *-i as a productive derivational suffix. The -i suffix in Ikoma does not condition sound changes of the preceding consonant. However, the final vowel -a is not realized after the causative suffix (see Laine et al., this issue). This is illustrated in (17).

<table><thead><tr><th>(17)</th><th>Ikoma</th><th>Causal</th></tr></thead><tbody><tr><td></td><td>Noncausal</td><td>Noncausal</td></tr><tr><td></td><td>a. <i>book-a</i> 'wake up (intr.)'</td><td><i>book-i</i> 'wake up (tr.)' (but not <i>book-y-a</i>)</td></tr><tr><td></td><td>b. <i>jááj-a</i> 'melt (intr.)'</td><td><i>jááj-i</i> 'melt (tr.)' (but not <i>jááj-y-a</i>)</td></tr></tbody></table>

In a set of 27 noncausal/causal verb pairs in Ikoma, 17 are in causative correspondence; that is, the causal verb is derived using the causative suffix *-i not present in the noncausal verb (Laine et al., this issue). Moreover, cognates of the Ikoma suffix *-i are attested in three other languages that form the genealogical Western Serengeti group with Ikoma: Nata ([ntk]; JE45), Ishenyi ([ntk]; JE45) and Ngoreme ([ngq]; JE401) (Laine et al., this issue).

Swahili has retained a reflex of PB *-i after labials, as in (18a), and sometimes after nasals, as in (18b). In other contexts, the reflex of the PB causative suffix *-i is lost (Nurse & Hinnebusch 1993: 370). The verb pair in (18b) is the only Swahili noncausal/causal pair from Haspelmath's (1993) verb list in causative correspondence where the causal verb is derived by the causative suffix -y.

<table><thead><tr><th>(18)</th><th>Swahili</th><th>Causal</th></tr></thead><tbody><tr><td></td><td>Noncausal</td><td>Noncausal</td></tr><tr><td></td><td>a. <i>ogop-a</i> 'fear'</td><td><i>ogof-y-a</i> 'frighten'</td></tr><tr><td></td><td>b. <i>pon-a</i> 'improve (intr.)'</td><td><i>pon-y-a</i> 'improve (tr.)'</td></tr></tbody></table>

In contrast to Ikoma -i, the Swahili suffix -y is no longer productively used to code causative derivation, and verbs such as those in (18) are fossilized. Instead, the productive causative suffixes in Swahili are -ish (e.g. *zam-a/zam-ish-a* 'sink (intr./tr.)') and -iz (e.g., *pend-a/pend-ez-a* 'love/please').

Ikoma and Swahili illustrate that noncausal/causal verb pairs with reflexes of the PB causative *-i need not undergo any morphophonological changes, and thus retain a causative correspondence type. However, most verbs historically derived by reflexes of PB *-i in East Bantu languages have under-
gone morphophonological changes that have altered the stem's morphological structure. As a result, the correspondence types of these verb pairs have changed from causative to ablaut, partial suppletive or equipollent. We discuss these correspondence types in the following subsections.

## 4.2 Verb pairs in ablaut correspondence

As shown in Section 3, reflexes of PB causative *-i can cause mutations of causal verb stems. The most widespread effect of the morphophonological changes conditioned by reflexes of the PB suffix *-i is the frication of the preceding consonant resulting in a fricative or affricate (Bastin 1986: 131-140). This is observed in Swahili (19) and the five Greater East Ruvu languages under investigation in this paper, as illustrated for Kagulu in (20). In (19) and (20), the historical application of the causative suffix -y triggered the frication of the final consonant of the stem, e.g. *k > sh* in (19), *k > s* in (20a) and *l > s* in (20b-c). Following frication, the causative -y suffix became absorbed. Evidence of the suffix at an earlier stage is the frication of the stem-final consonant.

(19) Swahili
Noncausal
wak-a 'burn (intr.)'
Causal
wash-a 'burn (tr.)' (< *wak-y-a*)

(20) Kagulu
Noncausal
a. ak-a 'burn (intr.)'
b. hol-a 'cool (down) (intr.)'
c. kul-a 'grow (intr.)'<fnref n="12" />
Causal
as-a 'burn (tr.)' (< *ak-y-a*)<fnref n="10" />
hos-a 'cool (down) (tr.)'<fnref n="11" /> (< *hol-y-a*)
kus-a 'grow (tr.); cultivate' (< *kul-y-a*)

We argue that these noncausal/causal verb pairs are in ablaut correspondence. This correspondence type has a “difference of vowel or consonant grade in root or stem, but no difference in formal morphological composition” (Nichols et al. 2004: 159). There is one ablaut verb pair observed in each of the other four Greater East Ruvu languages, all of which are cognate with Kagulu *hol-a/hos-a* (20b): *hol-a/hots-a* in Luguru and *hol-a/hoz-a* in Kutu, Kwere and Zaramo.

There are two Swahili verb pairs from the sample that might be considered ablaut, but the formal relationship of consonant alternation is not overtly visible due to an additional sound change that deletes /l/ in stem-final position. We present the Swahili verb pairs and corresponding Proto-Bantu reconstructions in (21a-b).

(21) Proto-Bantu
Swahili
Noncausal
a. *kód 'grow up (intr.)'
b. *pód 'be cold, cool down (intr.); be quiet'
Causal
ku-a 'develop'
po-a 'cool down'
kuz-a 'develop (tr.)' (< *kul-y-a*)
poz-a 'cool (down) (tr.)'<fnref n="13" />
(< *pol-y-a*)

On a first examination, the verb pairs seem to be of the causative correspondence type, because the causal verbs appear to be derived from the noncausal verbs by adding a suffix -z. However, Swahili

<footnote n="10">10. Swahili *wak-a/wash-a* (19) and Kagulu *ak-a/as-a* (20a) are cognate.</footnote>

<footnote n="11">11. The meaning 'cool down (intr./tr.)' was added in the questionnaire by Dom *et al.* (2021) as a conceptual synonym to 'freeze (intr./tr.)' from Haspelmath's (1993) list.</footnote>

<footnote n="12">12. The meaning 'grow (intr./tr.)' was elicited in Kagulu as a conceptual synonym to 'develop (intr./tr.)' from Haspelmath's (1993) list.</footnote>

<footnote n="13">13. This verb pair is not included in the Swahili dataset from Yoneda (2014c), as it is based on the list from Haspelmath (1993) where the meaning 'cool down (intr./tr.)' is not included (but see Dom *et al.* 2021).</footnote>
has a sound change which deletes the consonant /l/ as the reflex of PB *d, but only in the stem-final position (Nurse & Hinnebusch 1993: 100). The Proto-Bantu reconstructions of the noncausal Swahili verbs in (21a-b) have *d in stem-final position. The roots of the noncausal Swahili verbs have /l/ as reflex of that PB *d, i.e. *kul* and *pol* from *kód* and *pód*, which is deleted. The underlying forms with /l/ are used in Swahili when derivational suffixes are attached to the root, for example, with the ap- plicative suffix -i/-e, as in *kul-i-a* ‘develop for’ and *pol-e-a* ‘cool down for’. In such derived forms, the /l/ from the verb root is not deleted because the consonant is not in stem-final position. Importantly, the causal verbs *kuz-a* and *poz-a* in (21a-b) are reflexes of the phonologically “full” roots *kul* and *pol* derived with the reflex of PB *-i*, i.e. *kuz-a* < *kul-y-a* and *poz-a* < *pol-y-a*. Taking into consideration the allomorphs *kul* and *pol*, which are the etymologically older forms of these roots but only used synchronically in derivational forms, the verb pairs in (21) could be considered as having an ablaut instead of a causative correspondence.

### 4.3 Verb pairs in partial suppletive correspondence

In some Bantu languages, the lenition process conditioned by reflexes of the PB high vowels *i* and *u* has developed further, resulting in the loss of the preceding consonant (Section 3). This sound change is observed in Matengo, where the stem-final consonant is deleted before a high vowel such as a reflex of the PB causative suffix *-i*. In addition to this change, the reflex of the PB causative suf- fix *-i* is lost altogether. There are three verb pairs in the Matengo noncausal/causal dataset in which these morphophonological changes are observed:

(22) Matengo noncausal/causal verb pairs with reflexes of PB *-i* (Nobuko Yoneda p.c.)

<table><thead><tr><th>Noncausal</th><th>Causal</th></tr></thead><tbody><tr><td>a. <i>book-a</i> ‘move (intr.)’</td><td><i>boo-a</i> ‘move (tr.) (<i>*book-y-a</i>)<sup>14</sup></td></tr><tr><td>b. <i>hɔb-a</i> ‘get lost’</td><td><i>hɔ-a</i> ‘lose (tr.)’ (<i>*hɔb-y-a</i>)</td></tr><tr><td>c. <i>bel-a</i> ‘boil (intr.)’</td><td><i>be-a</i> ‘boil (tr.)’ (<i>*bel-y-a</i>)</td></tr></tbody></table>

We propose that these pairs are in partial suppletive correspondence. This correspondence type describes a formal relation in which the two members of the noncausal/causal verb pair “are partly cognate but not related by any direct morphological process” (Nichols et al. 2004: 159). In other words, the noncausal and causal stems in (22) are partly cognate, sharing all but the final consonant of the stem. Crucial to this categorization is that there is no evidence that stem-final consonant deletion is a productive derivational process to form causative verbs from non-causative verbs in Matengo or, vice versa, that stem-final consonant insertion is a regular derivational mechanism for anticausativization.

### 4.4 Verb pairs in equipollent correspondence

Verb pairs in which the noncausal and causal verb are derived from the same root (i.e. are in equipollent correspondence) are frequent in the East Bantu languages explored in this study. One particular suffix alternation, illustrated in (23), is attested in all eight languages examined in this study. The suffixes are called “separative intransitive” and “separative transitive” in Bantu linguistics and reconstructed to PB as *-ʊk and *-ʊd* (Meeussen 1967: 92; Schadeberg & Bostoen 2019: 173).

<footnote n="14">14. Repeated from (16) (see also Hinnebusch 1981: 37). In contrast to Hinnebusch (1981: 37) and Nobuko Yoneda (p.c.), Janson (2007: 83) suggests that consonants in Matengo have undergone lenition to /h/ before high vowels. We follow Nobuko Yoneda (p.c.) here.</footnote>
(23) Equipollent noncausal/causal verb pairs with reflexes of the PB suffix *-ʊk/*-ʊd

<table><thead><tr><th></th><th>Noncausal</th><th>Causal</th></tr></thead><tbody><tr><td>a. Ikoma</td><td><b>iγ-ok-a</b> 'open (intr.)'</td><td><b>iy-or-a</b> 'open (tr.)'<sup>15</sup></td></tr><tr><td>b. Matengo</td><td><b>hog-ok-a</b> 'open (intr.)'</td><td><b>hog-ol-a</b> 'open (tr.)'</td></tr><tr><td>c. Swahili</td><td><b>in-uk-a</b> 'rise'</td><td><b>in-u-a</b><sup>16</sup> 'raise'</td></tr><tr><td>d. Kagulu</td><td><b>bid-uk-a</b> 'be(come) changed, change (intr.);<br>turn (intr.)'</td><td><b>bid-ul-a</b> 'change (tr.);<br>turn (tr.)'</td></tr><tr><td>e. Kutu</td><td><b>lumb-uk-a</b> 'be(come) melted, melt (intr.)'</td><td><b>lumb-ul-a</b> 'melt (tr.)'</td></tr><tr><td>f. Kwere</td><td><b>fung-uk-a</b> 'be(come) open, open (intr.)'</td><td><b>fung-ul-a</b> 'open (tr.)'</td></tr><tr><td>g. Luguru</td><td><b>megh-uk-a</b> 'be(come) split, split (intr.);<br>burst (intr.)'</td><td><b>megh-ul-a</b> 'split (tr.);<br>burst (tr.)'</td></tr><tr><td>h. Zaramo</td><td><b>hind-uk-a</b> 'be(come) turned, turn (intr.)'</td><td><b>hind-ul-a</b> 'turn (tr.)'</td></tr></tbody></table>

All the languages examined in this study exhibit equipollent verb pairs with causal verbs historically derived by reflexes of PB *-i. In Ikoma, the causative suffix -i alternates with either the separative intransitive -ok (24a), the passive -u (24b) or the neuter -ek (24c).

(24) Ikoma equipollent verb pairs with the reflex of PB *-i

<table><thead><tr><th></th><th>Noncausal</th><th>Causal</th></tr></thead><tbody><tr><td>a. <b>hiif-ok-a</b> 'boil (intr.)'</td><td><b>hiif-i</b> 'boil (tr.)'</td></tr><tr><td>b. <b>mer-u</b> 'sink (intr.)'</td><td><b>mer-i</b> 'sink (tr.)'</td></tr><tr><td>c. <b>sar-ek-a</b> 'destroy (intr.)'</td><td><b>sar-i</b> 'destroy (tr.)'</td></tr></tbody></table>

In Swahili and the Greater East Ruvu languages, the equipollent pairs from the datasets can be divided into two groups: (i) causal verbs derived by a suffix ending in an affricate or fricative, and (ii) causal verbs derived by a suffix ending in a different consonant type. Examples of the first group are given in (25). The equipollent verb pairs in (23) belong to the second group.

(25) Equipollent verb pairs with the suffix -Vts, -Vsh, -Vs or -Vz on the causal verb

<table><thead><tr><th></th><th>Noncausal</th><th>Causal</th></tr></thead><tbody><tr><td>a. Kagulu</td><td><b>hem-ul-a</b> 'be(come) boiled;<br>boil (intr.)'</td><td><b>hem-us-a</b> 'boil (tr.)' (< *hem-ul-y-a)</td></tr><tr><td>b. Kutu</td><td><b>bimbil-ik-a</b> 'roll (intr.)'</td><td><b>bimbil-is-a</b> 'roll (tr.)' (< *bimbil-ik-y-a)</td></tr><tr><td>c. Kwere</td><td><b>gidim-il-a</b> 'sink (intr.)'</td><td><b>gidim-iz-a</b> 'sink (tr.)' (< *gidim-il-y-a)</td></tr><tr><td>d. Luguru</td><td><b>lak-al-a</b> 'be(come) burned;<br>burn (intr.)'</td><td><b>lak-ats-a</b> 'burn (tr.)' (< *lak-al-y-a)</td></tr><tr><td>e. Swahili</td><td><b>yey-uk-a</b> 'melt (intr.);<br>dissolve (intr.)'</td><td><b>yey-ush-a</b> 'melt (tr.);<br>dissolve (tr.)' (< *yey-uk-y-a)</td></tr><tr><td>f. Zaramo</td><td><b>tog-ot-a</b> 'be(come) boiled;<br>boil (intr.)'</td><td><b>tog-os-a</b> 'boil (tr.)' (< *tog-ot-y-a)</td></tr></tbody></table>

<footnote n="15">15. Ikoma uses -uk/-ůr after roots with /u/, a/, the allomorphs -ok/-o̊r following /i, e, ε, o/, and -ɔk/-ɔr if the root contains the vowel /ɔ/ (Higgins 2012: 184).</footnote>

<footnote n="16">16. The Swahili suffix -u is an allomorph of -ul and a regular reflex of PB *-ʊd where stem-final /l/ is deleted (Nurse & Hinnebusch 1993: 100).</footnote>
We claim that the causal verbs in (25) are derived by the PB suffix *-i. In earlier stages of these languages, the form of the causal verbs in (25) was *ROOT-VC-y-a*, and the verb pairs were in causative correspondence. For example, in Kagulu, the verb *hem-us-a* ‘boil (tr.)’ in (25a) is the reflex of the older form *hem-ul-y-a*. The addition of the causative suffix -y conditioned the same types of morphophonological changes as we have observed with verb pairs in ablaut correspondence (Section 4.2).<fnref n="17" /> After the absorption of the reflex of PB causative *-i in these languages, the formal relationship between the noncausal and causal members changed from causative to equipollent. Parallel to our proposal that the verb pairs in Section 4.2 should be analyzed as being of the ablaut correspondence type, the coding of causativity has shifted from derivation by suffix (causativization) to stem-final consonant alternation. Unlike those ablaut pairs in Section 4.2, the stem-final consonants of the causal verbs in (25) are part of a derivational suffix instead of the verb root.

Equipollent pairs with reflexes of PB *-i are more frequent than those with other suffixes (as in (23)) in the Swahili and Greater East Ruvu datasets. For Swahili, 15 out of a total of 20 equipollent pairs have a reflex of a causal verb with PB *-i, 8/14 in Kagulu, 10/16 in Kutu, 12/17 in Kwere, 11/16 in Luguru and 8/14 in Zaramo. This frequency suggests that the use of reflexes of PB *-i in these languages was quite productive in earlier stages of these languages to derive causative verbs from morphologically complex non-causative verbs.

The equipollent pairs in Ikoma (24), on the one hand, and Swahili and Greater East Ruvu (25), on the other hand, are not structurally identical. In Ikoma, the causative suffix -i is attached to the root and alternates with the derivational suffix of the noncausal verb, i.e. -ok, -u and -ik. In Swahili and Greater East Ruvu, the causal verbs were formed by adding the reflex of the PB suffix *-i to the derived noncausal stem.

Matengo presents the third pattern for equipollent noncausal/causal pairs suffixed with the PB causative *-i. In Matengo, the derivational suffix on the causal verb corresponds to the suffix of the noncausal verb but lacks its final consonant. This is illustrated in (26).

(26) Matengo verb pairs with -VC/-V suffix alternation in equipollent correspondence

<table><thead><tr><th></th><th>Noncausal</th><th>Causal<sup>18</sup></th></tr></thead><tbody><tr><td>a.</td><td><b>jim-uk-a</b> ‘wake up (intr.)’</td><td><b>jim-u-a</b> ‘wake up (tr.)’ (<b>*jim-uk-y-a</b>)</td></tr><tr><td>b.</td><td><b>ny-uk-a</b> ‘rock (intr.)’</td><td><b>ny-u-a</b> ‘rock (tr.)’ (<b>*ny-uk-y-a</b>)</td></tr><tr><td>c.</td><td><b>sus-uk-a</b> ‘go out’</td><td><b>sus-u-a</b> ‘put out’ (<b>*sus-uk-y-a</b>)</td></tr></tbody></table>

The formal alternation between the members of the verb pairs in (26) is similar to the partial suppletive correspondence of morphologically basic verbs in Matengo (Section 4.3). Just as in the partial suppletive pairs, the causal verbs lack the stem-final consonant of the noncausal verb form. However, because the verb stems in (26) are morphologically complex, these verb pairs are in equipollent correspondence. That is, both members of the verb pairs in (26) are morphologically derived but with different forms.

<footnote n="17">17. In Swahili, Kutu, Kwere and Zaramo, the voice feature of the mutated consonant is maintained in the frication process. Compare Swahili *yey-ush-a* ‘melt, dissolve (tr.)’ (<b>*yey-uk-y-a</b>) with *tand-az-a* ‘spread (tr.)’ (<b>*tand-al-y-a</b>). In contrast, Kagulu and Luguru have lost the voice opposition, e.g. Luguru *lumb-uts-a* ‘melt (tr.)’ (<b>*lumb-uk-y-a</b>) and *lak-ats-a* ‘burn (tr.)’ (<b>*lak-al-y-a</b>).</footnote>

<footnote n="18">18. The suffix -u on the Matengo causal verbs in (26) is identical in shape to Swahili -u, e.g. *in-u-a* ‘raise’ in (23c). However, these formally identical suffixes have different origins. In Swahili, the suffix -u is an allomorph of -ul, a reflex of the PB separative transitive suffix *-od. In Matengo, the suffix -u is a reflex of the historical compound *-uk-y, that is, the separative intransitive + causative. Interestingly, the sound change in Swahili that deletes stem-final /l/, conditioning the -ul/allomorph, is also observed in Matengo. For instance, in the equipollent noncausal/causal verb pair *nyung*’*any-uk-a*/*nyung*’*any-u(l)-a ‘melt; dissolve (intr./tr.)’, the suffix on the causal verb is attested with a -VC or -V shape (Yoneda 2014b). The sound change is still in an initial stage in Matengo, with other causal verbs having only the original form, e.g. *tumb-uk-a/tumb-ul-a* ‘begin (intr./tr.)’ (Yoneda 2014b). If the loss of stem-final /l/ becomes more advanced in Matengo, causal verbs with a suffix -u will have two possible historical pathways that could underlie the synchronic form, i.e. derivation by a reflex of PB *-i or loss of stem-final /l/ with the suffix -ul.</footnote>
Like the equipollent pairs in Swahili and the Greater East Ruvu languages in (25), the Matengo pairs were in causative correspondence in an earlier stage but are now in equipollent correspondence.

## 4.5 Summary

In this section, we have examined the correspondence types of noncausal/causal verb pairs in which reflexes of verb stems historically derived with PB *-i are attested across eight East Bantu languages. In earlier stages of these languages, reflexes of PB *-i were used to derive causal verbs and thus the verbs were causative correspondence. Some of the verb pairs in Ikoma and Swahili remain in causative correspondence. For others, we propose that after a series of sound changes involving lenition of the consonant preceding the reflex of PB causative *-i and the loss of the reflex of *-i in all languages except Ikoma, the formal relation between the noncausal and causal members changed from causative to ablaut, partial suppletive or equipollent. Table 2 summarizes the classification of correspondence types in each language, according to our analysis.

<table><caption>Table 2 — Summary of correspondence types for noncausal/causal verb pairs involving reflexes of PB *-i in eight East Bantu languages.</caption><thead><tr><th></th><th>Causative</th><th>Ablaut</th><th>Partial suppletive</th><th>Equipollent</th></tr></thead><tbody><tr><td>Ikoma</td><td>√</td><td>—</td><td>—</td><td>√</td></tr><tr><td>Swahili</td><td>√</td><td>√</td><td>—</td><td>√</td></tr><tr><td>Kagulu</td><td>—</td><td>√</td><td>—</td><td>√</td></tr><tr><td>Kutu</td><td>—</td><td>√</td><td>—</td><td>√</td></tr><tr><td>Kwere</td><td>—</td><td>√</td><td>—</td><td>√</td></tr><tr><td>Luguru</td><td>—</td><td>√</td><td>—</td><td>√</td></tr><tr><td>Zaramo</td><td>—</td><td>√</td><td>—</td><td>√</td></tr><tr><td>Matengo</td><td>—</td><td>—</td><td>√</td><td>√</td></tr></tbody></table>

Ikoma and Swahili are the only languages in which noncausal/causal pairs with the causative suffix *-i are in causative correspondence (Section 4.1). In Ikoma, the causative suffix *-i also features in equipollent pairs, where it alternates with intransitivizing suffixes on the noncausal members (Section 4.4).

In Swahili and the Greater East Ruvu languages, most verbs derived with reflexes of PB *-i underwent a series of morphophonological changes that resulted in the frication of the consonant preceding the suffix as well as the loss of the segmentable reflex of the causative suffix (Section 3). In verb pairs with a morphologically basic noncausal verb, an originally causative correspondence has shifted to an ablaut correspondence (Section 4.2). Reflexes of PB *-i were historically also used to derive causal verbs from morphologically derived noncausal verbs. In these cases, the correspondence type has shifted from causative to equipollent (Section 4.4).

In Matengo, verb stems involving reflexes of PB *-i underwent additional innovations subsequent to the frication of consonants preceding the vocalic causative suffix. These changes ultimately resulted in the loss of both the consonant preceding the suffix *-i as well as the reflex of the suffix itself (Section 3). Noncausal/causal verb pairs with a causative correspondence involving the reflex of PB *-i developed into an alternation involving root-final consonant deletion, such as *bel-a* ‘boil (intr.)/*be-a* ‘boil (tr.)’. This type of formal alternation is unproductive and synchronically unconditioned in Matengo, and therefore shifted from causativization to partial suppletion (Section 4.3). A similar alternation of stem-final consonant deletion is observed for verb pairs with morphologically derived noncausal verbs, to which the reflex of PB *-i was added to form the corresponding causal verb. In these verb pairs, the suffix compounds -VC-y on causal stems changed into -V, alternating with -VC suffixes on
the noncausal verb stems. The restructuring from a suffix compound (-VC-y) to a simple vocalic suffix (-V) on the causal verb shifted the formal relation between the members of such pairs from a causative to an equipollent one.

## 5. CONCLUSIONS

Analyzing data from eight East Bantu languages, we have argued that for many noncausal/causal verb pairs, the causal verb has undergone morphophonological changes conditioned by reflexes of the Proto-Bantu causative suffix *-i. Cross-linguistic research on the noncausal/causal alternation has focused on determining the (variation of) formal relations between the two members of alternating pairs. Expanding on Haspelmath's (1993: 90-92) five correspondence types, Nichols et al. (2004: 159) propose a more fine-grained typology of correspondence types. While earlier analyses of noncausal/causal pairs in Bantu languages use Haspelmath's classification (see Haspelmath 1993; Yoneda 2014a; 2014b; 2014c), we have shown that a selection of East Bantu languages illustrate the usefulness of some of Nichols et al.'s (2004) more fine-grained categories. Our analysis reveals that these noncausal/causal verb pairs involving reflexes of the PB suffix *-i were in causative correspondence in earlier stages of the languages. However, following morphophonological changes that resulted in lenition or loss of the stem-final consonant, and, in some cases, the loss of the causative suffix as well, the correspondence types of these verb pairs have changed into ablaut, partial suppletion or equipollence.

Our analysis differs from a diachronically-oriented analysis, such as the one presented by Yoneda (this issue) for Swahili. While our analysis proposes a shift from a previously causative correspondence to other types, Yoneda argues that the formally altered causal verbs have an underlying form with the suffix -y, i.e. the segmentable reflex of PB *-i. In Yoneda's approach, these verb pairs do not change correspondence type and are considered causative. These different approaches highlight the complexities that arise when applying categories emerging from typological research to individual languages while also taking into account diachronic morphophonology.

The changes in correspondence type of noncausal/causal verb pairs in Bantu languages have implications for the typological profile of individual languages with respect to basic valence orientation (Nichols et al. 2004). Nichols et al.'s study suggests that detransitivizing languages have a predominance for the anticausativization strategy, transitivizing languages prefer the causativization strategy, neutral languages favor formal marking of both members of noncausal/causal pairs (the equipollent strategy), and indeterminate languages have a preference for morphologically basic noncausal/causal pairs (the labile strategy). The analysis proposed in this paper points to noncausal/causal pairs in Swahili and Greater East Ruvu languages having a predominance of equipollence. With a relatively high proportion of equipollent pairs that involve reflexes of the PB causative suffix *-i, and thus, historically in causative correspondence (Section 4.4), these languages may have shifted from a transitivizing to a neutral basic valence orientation. We leave the exploration of this issue for further research.

## ACKNOWLEDGEMENTS

We are grateful to the attendants of the workshop *The noncausal/causal alternation in African languages* at the 10th World Congress of African Linguistics, as well as the researchers of the BantUGent group and two anonymous reviewers for their comments on earlier versions of this paper. We would like to also extend our sincerest appreciation to the language consultants for their time and patience working with us. We thank the Swedish Research Council for funding this project.

## ABBREVIATIONS

* 1/2/3/... prefix corresponding to noun class 1/2/3/...

* 1/2/3SG 1st/2nd/3rd person singular

* C consonant
CAUS causative suffix

FV final vowel suffix

intr. intransitive

OBJ object index

PB Proto-Bantu

PRS present tense

SBJ subject index

tr. transitive

V vowel

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