Kipsigis verbs inflect for person and number agreement with the subject, mood (indicative, subjunctive, imperative), tense (non-past vs. three degrees of past), negation, and aspect (perfective vs. imperfective and simple vs. perfect) (Toweett 1979; Rottland 1982; Creider & Creider 1989).1 The language is largely agglutinative, but certain distinctions are expressed via suprasegmental material, such as tone or vowel length alternations, as we will see later. In verbal inflection, tense, negation, and subject agreement are expressed via prefixes, while (imperfective) aspect is expressed via a suffix. When they co-occur, they follow the template in (1), which is accompanied by an example of a negated, first-person singular form in the distant past imperfective.

The prefixes expressing tense and negation are generally invariable (modulo ATR harmony), while some subject agreement prefixes and the imperfective suffix have allomorphs which are conditioned by the particular TAM combination (as well as conjugation class, as we will see in a bit). The tonal melody of the inflected verbal stem is determined by TAM, conjugation class, and person: local person forms have a different melody from 3rd person forms across the paradigm. It has to be noted, however, that there is a limited understanding of verbal tonology in the language. The interested reader is referred to Creider (1980) and Creider & Creider (1989: 77–78, 83–84) for complete conjugation tables of Kipsigis and the related dialect Nandi respectively, but Tables 1, 2 provide a list of the tense and subject agreement prefixes, along with their allomorphs. The most common allomorphs for the imperfective suffix are -i and -e.2

Moving on to conjugation classes, according to traditional descriptions (e.g., Toweett 1979; Rottland 1982; Dimmendaal 1983), verbs in Kipsigis belong to one of two classes, called Class I and Class II in the Nilotic literature. The exact differences between the two inflectional paradigms depend on the particular TAM combination, but in most cases Class I and II differ in the vowel length of the subject agreement prefix, the imperfective allomorph and the overall tonal melody of the stem. This is illustrated in the non-past imperfective conjugation paradigm in (2). First, we observe that the subject agreement prefix for all local persons has a short vowel for the Class I verb t∫am ‘to like’, while it has a long vowel for the Class II verb kat ‘to greet’; in 3rd-person forms, there is no overt agreement morpheme in Class I, but a prefix i- in Class II. Second, the imperfective suffix has the form -e in Class I, but -i in Class II. Third, the tonal melody of the stem is different in the two paradigms. Also note that within each paradigm the melody is different for local person and third person forms; this person-driven tonal allomorphy holds across all cells of the verbal inflection paradigm, as mentioned earlier. The differences between Class I and Class II for the non-past imperfective are summarized in Table 3, noting that both the imperfective suffix and the tonal melody also depend on the number of syllables and length of the last vowel of the root, as will be explained in more detail in the next section.

In the next section, I provide arguments according to which the differences between Class I and Class II follow from the presence of an empty moraic prefix in Class II, without the need for conjugation class features in the grammar.

The argument for the presence of a moraic prefix in Class II verbs begins with the analysis of the i- prefix that we observe in 3rd person; the relevant form is repeated in (3) for convenience.

There are two possible ways of analyzing this morpheme: it could either be the 3rd person subject agreement allomorph for Class II or it could be a thematic element (akin a theme vowel) associated with Class II. I am going to argue in favor of the latter analysis, but with the twist that the thematic suffix is in fact an empty mora and i- is the epenthetic vowel filling this slot.

The clearest evidence against treating i- as a subject agreement prefix comes from its behavior with respect to vowel coalescence. Kipsigis has a regular phonological rule of vowel coalescence, where adjacent short vowels [a] and [i] merge into a long [e] (this rule is independent of ATR vowel harmony; see Kouneli 2019: 27–28 for more details).

The rule is active both in the nominal and the verbal domain, as can be seen in (5): the vowel of the thematic suffix coalesces with that of the secondary suffix (more details on these morphemes will be given in Section 4) in (5a), while the vowel of the current past tense morpheme coalesces with that of the second person agreement prefix in (5b).

What example (5b) shows is that verbal agreement prefixes are subject to vowel coalescence when adjacent to the current past tense prefix. The rule does not apply, however, in examples like (6) where /i/ is part of the (Class I) verbal stem, and not an agreement prefix. This may be because of the intervening (covert) 3rd person agreement morpheme or because of a morphological domain boundary (presumably the agreement prefix is closer to tense than the root is).

The (non-)application of vowel coalescence thus makes predictions regarding the [i] vowel appearing on 3rd person forms of Class II verbs. If [i] is an agreement prefix, we expect it to undergo vowel coalescence with the vowel of the past tense prefix (cf. (5b)). If, on the other hand, [i] is a thematic element associated with the verbal stem, coalescence may not apply (cf. (6)). What we observe in (7) is that coalescence between the tense prefix vowel and [i] is impossible, indicating that [i] is not an agreement morpheme, and is rather associated with the stem. This means that 3rd person agreement is zero for both Class I and Class II verbs, with i- in the latter class being a morpheme associated with Class II verbal stems.3

Further evidence against treating i- as a Class II 3rd person agreement prefix comes from imperatives. As can be seen in (8), the 2nd person singular imperative of Class I verbs does not bear any (overt) agreement morphology, while imperatives of Class II verbs appear with an i- prefix. Since these forms do not involve 3rd person, these data support the analysis of i- as a morpheme belonging to the stem of Class II verbs.4

Summing up, the morphophonological behavior of i- in Class II verbs supports its analysis as a thematic element, and not an agreement morpheme. This is also the consensus in previous literature. For example, Toweett (1979: 218) calls it a semi-thematic vowel and adds the phrase “or may be it is thematic”. Similarly, Dimmendaal (1983) argues that Class II stems include an i- prefix, which he traces back to a Proto-Nilotic causative prefix *i-. Finally, Creider & Creider (1989: 81) write for the related dialect Nandi: “[a] large number of verbs have stems which begin with an initial vowel i-. Traditional analyses have posited two morphological classes on the basis of the separate segmental and tonal behaviour of regular verbs and the i- initial verbs.” While everyone seems to agree that the vowel [i] forms a unit with the verbal stem in Class II verbs, my analysis differs from previous descriptions in the following way: I argue that the thematic element is not underlyingly /i/, but rather an empty mora, which is filled by epenthetic [i] in certain cases.

The main evidence against positing an underlying /i/ comes from the form of the subject agreement prefixes. Going back to the inflection of Class II verbs in (2), we observe that the vowel of local person agreement prefixes is always long. This is a stable feature of Class II verbs across the paradigm: while agreement prefixes are short in most cells of the Class I inflectional paradigm, they are always long – without any exception – for Class II verbs.5 Thus, we have ɑːkɑt-i for ‘I greet’. The 1sg agreement prefix is /a/ underlyingly (as seen in the inflection of Class I verbs, but also the form of the pronoun: a-nɛː ‘I/me’). If the Class II verb kat ‘to greet’ had an underlying i- as a prefixal theme vowel, we would predict the following 1sg forms depending on whether vowel coalescence applies or not:

However, neither of these forms is grammatical. This shows that it is impossible for Kipsigis phonology to derive the correct form ɑː-kɑt-i if we assume an /i/ underlying vowel. Indeed, Creider & Creider (1989: 84) note the same problem for Nandi, namely that the general rules of vowel coalescence in the language cannot account for the behavior of the subject agreement vowels; they suggest morpheme-specific vowel coalescence rules just for the Class II i- prefix (for example, they argue that just in this case, [a] + [i] → [aː]).

However, in a theory that allows affixes to have the shape of a mora, i.e., empty prosodic structure (e.g., McCarthy & Prince 1986; Lombardi & McCarthy 1991; Flack 2007; Trommer 2014; 2015; Trommer & Zimmermann 2014), and under the assumption that morphological vowel lengthening can be modeled via the affixation of a mora and/or association of the vowel to a new mora (e.g., Hyman 1985; Hayes 1989; Zimmermann 2017), the Kipsigis facts receive a straightforward explanation if the thematic element of Class II verbs is a moraic prefix.

Assuming autosegmental representations (Goldsmith 1976 and subsequent work) that include moras, a surface form like ɑː-kɑt-i ‘I greet’, where a Class II verb is inflected for 1sg, has the underlying representation in (10).6

We therefore see that there is a floating mora (i.e., a mora that is not associated to segmental material) in the underlying representation. I propose that there is a constraint in Kipsigis that requires moras to be associated in the surface form. In the usual case, there is leftwards association, with the mora associating to the vowel of the subject agreement prefix, resulting in vowel lengthening. This can explain all cases of vowel lengthening of the subject agreement prefix, without resorting to morpheme-specific vowel coalescence rules such as those in Creider & Creider (1989). Apart from the local person prefixes, which we have already seen, this analysis predicts that the 3rd person allomorph kɔ- should also surface with a long vowel with Class II verbs. This prediction is borne out, as illustrated by the 3rd person perfective subjunctive form of the Class II kat ‘to greet’ in (11).

This leaves us with the vowel [i] which appears in 3rd person forms, as well as the imperative (cf. (8)). Looking at these forms, we observe that in this case there is no vowel to the left of the moraic prefix; therefore, the floating mora fails to associate, and I propose that an epenthetic vowel [i] is inserted as a repair.7 This pattern is reminiscent of mora augmentation processes in Japanese, where the additional mora leads to gemination, vowel lengthening or epenthesis (of a nasal) depending on the phonological enviropnement (e.g., Davis & Ueda 2002).8

The insertion of [i] to realize floating material is further motivated by an alternation in the formation of polar questions in Kipsigis. More specifically, polar questions are characterized by a clause-final H tone. However, the change in pitch is accompanied by segmental changes in the last word of the clause: vowel lengthening if the word ends in a vowel (12), but insertion of [i] if the word ends in a consonant (13).

Polar questions thus seem to be formed by a floating mora (and a H tone). If the mora attaches to a clause that ends in a vowel, it associates to the left (same as in the case of Class II verbs), but if it attaches to a consonant-final clause, then it fails to associate and [i] is inserted instead. Finally, it is worth mentioning that [i] is the general epenthetic vowel in the language: Toweett (1979) often refers to it as “epenthetic” (though he does not have a section dedicated to epenthesis), and it is also the vowel usually inserted in loanwords that violate Kipsigis phonotactics, as can be seen in (14), a loan from English ‘box’.9

Summing up the discussion so far, the differences between Class I and Class II verbs with respect to the vowel length of the subject agreement prefix follow straightforwardly from the presence of a moraic prefix in the latter case. This is in line with the description of Nandi in Creider & Creider (1989), who argue that the inflectional differences between Class I and Class II can be explained by regular phonology if we assume that Class II verbs have an i- thematic prefix. However, as was already explained, they need to resort to morpheme-specific phonology to account for the shape of subject agreement morphemes. Postulating a moraic prefix, on the other hand, avoids this problem: the general phonology of the language is enough, as evidenced by the similar behavior of polar question formation. It is also worth noting that mora affixation is common in Nilotic languages (see e.g., Flack 2007; Trommer 2011; 2015 on Dinka, Trommer 2014; Trommer & Zimmermann 2014 on Anywa, Trommer & Zimmermann 2014 on Päri, Remijsen & Ayoker 2020 on Shilluk), and has been used to explain complex morphophonological phenomena, including cases of subtractive morphology (Trommer & Zimmermann 2014).10 Kipsigis is thus added to the list of Nilotic languages that employ mora affixation.

So far, I have explained the differences between Class I and Class II verbs with respect to subject agreement morphology. Recall, however, that the two classes of verbs also differ in the allomorph of imperfective aspect, as well as in the overall tonal melody of the inflected stem. In the remainder of this section, I show that these differences also follow from the presence of a moraic prefix in Class II verbs.

Let’s start with the form of the imperfective suffix. If we look at the paradigm in (2), we observe that the imperfective suffix has the form -e for a monosyllabic Class I verb, but the form -i for a Class II verb with a monosyllabic root.11 The relevant difference is repeated in (15) below.

However, the distribution of these two aspect allomorphs (-e and -i) is best described in phonological terms, not in terms of conjugation class. Once we look at verbs of different phonological shapes, the generalization that emerges is the following: the default exponent of imperfective is the suffix -e, except in polysyllabic verbs (=verbs with two or more syllables) with a short vowel in the last syllable, where the allomorph -i is chosen. The Vocabulary Insertion rules are summarized in (16).12

Crucially, the phonological environment in (16b) refers to the stem, and not the root. This means that Class II verbs will always count as polysyllabic, since they contain a moraic prefix in addition to any root material.13 With the rules in (16) in place, the correct imperfective allomorph is derived for all forms known to me, with a summary provided in Table 4 (see also Toweett 1979: 188–192 for further examples).14 It becomes clear from this table that it is the prosodic shape of the stem, and not the conjugation class of the verb, that determines allomorph choice.15

Similar to the distribution of agreement prefixes, the choice of imperfective allomorph is therefore entirely determined by the presence of an additional mora on Class II verbs. This leaves us with the tonal differences between the two classes. Unfortunately, the discussion surrounding tone is preliminary at this stage, since there is, to my knowledge, no study of verbal tonology in Kipsigis. A cursory look at the examples in this section, however, reveals that the tonal melody of the stem varies depending on both vowel length and the number of syllables of the verb. Furthermore, a minimal pair is provided in (17) below, where a Class I verb has a different melody in 3rd person depending on the vowel length of the stem.16

This means that the presence of an additional mora in Class II, which is absent in Class I, will certainly have an effect on tonal inflection. Whether this will be enough to derive all tonal differences across the paradigm needs to be verified in future work, but preliminary data show that it is possible to reduce the tonal differences to the presence of the moraic prefix: as shown in (18), the tonal melody of a disyllabic Class I verb with a short vowel in the last syllable is the same as that of a Class II verb with a short vowel.

I have shown in this section that Class I verbs are morphologically unmarked, while Class II verbs contain a moraic thematic prefix; from now on only Class II will be glossed. The inflectional differences between the two classes of verbs can be explained by regular phonological processes once the presence of the additional mora in Class II is acknowledged. However, this has been adequately demonstrated only for part of the paradigm (e.g., we haven’t looked at perfect or subjunctive forms in detail), and further work on Kipsigis (especially tonal) phonology is needed before providing a detailed derivation of all forms. Despite the current limitations, big part of the inflection of Class II verbs can be clearly reduced to the presence of an additional morpheme in Class II (a morpheme that is acknowledged in all previous descriptions of the language); it would be surprising if other cells of the paradigm turned out to be different in a fundamental way. In the next section, I discuss the factors determining class membership.

Many verbs appear only in Class I or Class II. However, most verbs participating in the causative alternation (e.g., The cup broke vs. Mary broke the cup in English) do so by alternating between Class I (intransitive, anticausative variant) and Class II (transitive, causative variant), as illustrated in (19). More examples from my fieldnotes that participate in the Class I – Class II alternation include the following: sap ‘to heal’, tɔt ‘to rot’, t∫ɔːt ‘to melt’, t∫ʊs ‘to deflate’, nuːr ‘to soak’, piːt ‘to grow’.17

For those verbs that alternate, there is an additional phonological difference between the two classes: if the vowel of the last syllable of the verb is short in Class I, it is lengthened in Class II. This can be seen in (19) above, where the vowel of the verb bet ‘to lose’ is short in Class I, but long in Class II. If the verb already has a long vowel in Class I, no change occurs in Class II, as shown in (20), where the length of the verbal stem is invariable. This means that the vowel length of Class II can be predicted by the length of the Class I variant, but not vice versa; this is one more reason (in addition to the moraic prefix present in Class II) why Class II is taken to be marked compared to Class I.

According to Toweett (1979), about 60% of Kipsigis verbs alternate between Class I and Class II. The alternation is fully productive: derived verbs (e.g., all de-adjectival verbs) participate (21), as well as loanwords (22). The pair in (22) comes from the Swahili verbs chemka (intransitive) – chemsha (transitive) ‘to boil’.

About 40% of verbs, however, do not alternate between Class I and Class II: they occur only in one of the two classes. The vast majority of these verbs belong to Class I, which is in line with the phonological facts that point towards it being the unmarked class. Similarly, there are no emerging generalizations about the lexical semantics or transitivity of the verbs that belong to Class I. Toweett (1979) notes that out of 714 verbs in his sample, there are only 60 non-alternating Class II verbs, out of which 40 are transitive and 20 are intransitive.18

Before closing this section, it is worth noting that an alternation between the two classes is not the only way to participate in the causative alternation, with more strategies being available (see Kouneli 2021b for details). One strategy that may be of relevance is the addition of the causative morpheme -si, which obligatorily co-occurs with Class II morphology. An example is provided in (23), where the intransitive Class I verb jaːm ‘to dry’ forms its causative with the suffix -si, accompanied by a switch to Class II.19

While an extensive investigation of the causative suffix -si is still pending, it is mostly used to form causatives of change of state verbs (of the type illustrated in (23) above), as well as causatives of a variety of verbs which pattern with unergatives in other languages, as shown in (24).

It is, however, not possible to causativize transitive verbs with -si, with the exception of the following two: laːɲ ‘to climb’ and siːr ‘to pass/exceed’.20 Furthermore, in the case of change of state verbs, whether a verb will take -si in addition to the switch to Class II is lexically determined. The suffix, thus, does not show clear properties of productive morphological causatives cross-linguistically.

In what follows, I adopt the assumptions of Distributed Morphology: words are built in the syntax, with vocabulary items being inserted at terminal nodes post-syntactically. Of particular importance is the assumption that words are decomposed into a categorizing head and a root (Marantz 1997 a.o.); in the case of verbs, the categorizing head is assumed to be little v.

Furthermore, I follow work according to which both little v and Voice (Kratzer 1996) are present in the syntax. Little v is responsible for verbalizing the root and for providing event semantics, while Voice is responsible for introducing the external argument (Pylkkänen 2008; Harley 2013; Legate 2014 a.o.). I also adopt the ‘flavors of little v’ approach to the causative alternation (e.g., Folli & Harley 2005; 2007), according to which verbalizing heads come in different flavors, such as v_do, v_become and v_cause. Since the focus of this paper is on Class II verbs, most of which involve causative semantics, the flavors of little v that will be used are v_become and v_cause, the two heads typically used in analyses of the causative alternation (e.g., Pylkkänen 2008).21 Finally, it should be noted that whenever ‘causative semantics’ are mentioned in relation to Class II, what is meant is the interpretation associated with lexical causatives, since Class II is used to create the transitive variant of change of state verbs.22

I argue that there is no need for class features, with the moraic prefix of Class II being an overt verbalizer, in the same way that morphemes such as -ize, -ify etc. are overt verbalizers in English. Given the clear connection of Class II to the causative alternation in Kipsigis, I argue that the moraic prefix spells out v_cause. I further propose that this v_cause can either merge directly with the root or it can merge with an already categorized root, as illustrated in (25) below. These two structures correspond to non-alternating and alternating (=causative) Class II verbs, respectively.

Both the spellout and the interpretation of v_cause will depend on whether it appears in the root-selecting (25a) or verb-selecting structure (25b). Starting with the phonological effects, recall that for verbs that alternate between Class I and Class II, there is a regular process of lengthening of the vowel of the final syllable of the verb in the causative variant; the relevant example is repeated here as (26).

Thus, both non-alternating and alternating Class II verbs come with a moraic prefix, but only the latter exhibit lengthening of the vowel of their last syllable. In order to capture the similarity (=presence of the moraic prefix) between the two structures, I propose that v_cause is always spelled out as a mora, as in (27), irrespective of whether v_cause is in (25a) or (25b).

This leaves us with the vowel lengthening effect for alternating verbs. Here, we observe that these verbs come with more structure, as two verbalizing heads are stacked. I see (at least) two possible solutions, but unfortunately it is not clear at this stage how to choose between them. First, it is possible that vowel lengthening in the last syllable of the root is a regular (morpho)phonological process caused in the context of two stacked verbalizing heads. In order to evaluate the validity of this claim, one would have to investigate other contexts of stacking of little v’s and see if lengthening obtains there as well. Unfortunately, I do not currently have access to such data. Second, it may be that v_cause has two allomorphs: a moraic prefix in the context of a root, but a moraic circumfix (i.e., a mora that associates to the edges of the root) in the context of another verbalizer, as in (25b). This solution seems attractive in light of the shape of the L.H₀.L nominative tonal melody for nouns in the language, where a low tone associates to the first and last syllable, with high tones in the intermediate syllables (Kouneli & Nie 2021). This melody has been recently analyzed by Jolin (2022) via reference to edge-in association along the lines of Yip (1988). Nevertheless, a potential problem arises, which means that further research is needed to see whether this is indeed a viable solution: in polar question formation, the affixation of a mora leads to epenthesis of [ɪ] if the word ends in a consonant, whereas in this case, the mora is able to ‘skip’ a final consonant and cause lengthening inside the syllable. Of course, many differences exist between polar questions and causative verbs (e.g., the polar question question particle certainly comes at a later cycle, when words are already formed), which may be able to explain the different behavior of the moraic affix in the two cases. More research on the phonology of moraic affixes in Kipsigis is needed to resolve this issue.

Moving on to the interpretation of v_cause in the two constructions, we observe that in the verb-selecting structure, the verb is always the lexical causative of a change of state verb. Therefore, v_cause has in this case ‘regular’ causative semantics, of the type that is proposed for the causative variant in theories of the causative alternation that employ flavors of little v. Indeed, the structure in (25b) is identical to the structure proposed for marked causatives in those theories (e.g., Folli & Harley 2005; Pylkkänen 2008), with the lower v usually identified as v_become.23 Since in Kipsigis the only morphological distinction is between causatives (Class II) and everything else (Class I), I will not be representing other types of little v here (e.g., v_become, v_do), but given the semantics of other classes, it is of course entirely plausible that these flavors of little v exist, but have only semantic effects.

As for the root-selecting structure, it is important to note that the vast majority of non-alternating verbs in Kipsigis belong to the unmarked Class I, with only 60 out of 714 verbs in Toweett’s sample being Class II. Out of these 60 verbs, 40 are transitive with relics of causative semantics. This means that they tend to be agentive, historically related to verbs that alternated, or verbs that have a lexical causative component without having a corresponding intransitive (e.g., neːt ‘to teach’). Thus, I propose that verbs in Kipsigis are generally formed by merging a silent little v (descriptively Class I) with a root. A small class of verbs, however, are formed by merging a root with v_cause (the structure in (25a)). These are the non-alternating Class II verbs. For some of them, v_cause will have the lexical causative meaning. For others, it will receive an idiosyncratic interpretation depending on the root. This follows from the fact that v_cause directly merges with the root in this case, and the first-categorizing head is assumed to delimit the domain for idiosyncratic interpretation (Marantz 1997 and subsequent work). Therefore, non-alternating Class II verbs do not have obvious causative semantics; the interpretation will depend on the particular root.

Given the clear connection of Class II to the causative alternation, a question that may arise at this point is whether there is independent evidence for locating the moraic prefix on little v, rather than on some other verbal projection; possible candidates for such a projection include Voice or even a dedicated Caus head (e.g., Key 2013; Harley 2017). The first clear shortcoming of this alternative is that if the moraic prefix spelled out Voice or Caus, it would be difficult to account for its presence on non-alternating verbs without causative semantics; its analysis as a verbalizer allows us to capture both its uses in a uniform way. There are, however, further arguments in favor of a little v analysis, which are discussed in detail in Kouneli (2021b). Two of the main arguments are summarized below.

I begin with the evidence from reduplication. Kipsigis has productive verbal reduplication expressing multiple events.24 An example of reduplication of a (Class II) verb with a long vowel, twaːl ‘to jump’, is shown in (28).25

When the verb undergoing reduplication has a short vowel, a linking affix -aa- is present between the two copies of the root, as shown in (29).

Recall now that alternating verbs with a short vowel have a long vowel in Class II. The sensitivity of the linking vowel -aa- to vowel length allows us to determine the order of application of reduplication relative to Class II determination. If reduplication applies before merging the head responsible for lengthening, then we expect those verbs to appear with a linking vowel in reduplicated contexts; this vowel should be absent if the head responsible for vowel lengthening merges before reduplication applies. We observe the latter in the data. As shown in (30), the reduplicated form of the Class I verb sap ‘to heal (intransitive)’ has a linking vowel since the verb has a short vowel. The crucial data point is the behavior of its Class II counterpart saːp ‘to heal (transitive)’; as shown in (30b), no linking vowel appears in this case, indicating that at the point when reduplication applies, the root has already undergone vowel lengthening.

Verbal reduplication expresses event plurality, and thus a straightforward assumption is that it targets little v, i.e., the head responsible for event semantics. Since Class II information for alternating verbs (i.e., vowel lenthening) is present before the application of reduplication, these data support the claim that Class II is the spellout of a little v head.26

The strongest piece of evidence in favor of placing the Class II moraic prefix on little v comes from nominalizations. There is a debate in the literature about ‘how much’ functional structure is embedded in complex event nominals, especially with respect to Voice (see Alexiadou 2001; 2017; Wood 2019 and references therein). It is uncontroversial though that result nominals do not embed Voice; they always embed very small verbal structures corresponding to a verbalized root (vP).27 Interestingly, all Kipsigis nouns that are derived from Class II verbs (whether they alternate or not) contain a prefix kaː-, which is the nominal allomorph of the verbalizing head associated with Class II (Toweett 1979; see also Creider & Creider 1989 for Nandi). In (31) you see the (non-event) nominalization of the non-alternating transitive verb kat ‘to greet’, while (32) shows the nominalization of an alternating verb.

What is important to note here is that kaː- does not do any nominalizing work: it is the suffix in both (31) and (32) that is responsible for the nominalization.28 What this means is that kaː- simply indicates the presence of v_cause in the structure being embedded. This prefix is present in all types of nominalizations; while (31) is a result nominal, (33) below shows an agent nominalization from a Class I verb in (33a) and from a Class II verb in (33b). This minimal pair nicely illustrates how kaː- simply shows that a ‘Class II structure’ is being embedded, without doing any nominalizing work itself.

The most straightforward analysis of kaː- is as the spellout of our overt verbalizer in the context of a nominal head. More specifically, assuming the structure in (34) for nominalizations, we can postulate the VI rule in (35) for kaː-: this prefix is the allomorph of v_cause in the context of little n.

Before concluding the analysis section, it is worth saying a couple of words about the causative suffix -si, which is also used in the causative alternation, as well as to form causatives of verbs that are usually classified as unergatives in other languages (see Section 2.3). An important feature of this suffix is that it always co-occurs with the moraic prefix of Class II. The most straightforward assumption about it is, thus, that is spells out a separate head, most likely above vP. The obvious candidate is a dedicated Caus head. If this is indeed the case, then at least two predictions are made: i) verbs with -si must always have causative semantics (unlike Class II verbs which could have idiosyncratic meanings if v_cause is root-selecting), and ii) -si should be a productive morphological causative. The first prediction is borne out, as there are, to my knowledge, no verbs that take -si and do not have clear transitive syntax and causative semantics. The second prediction is trickier, since -si seems to be lexically determined with some change of state verbs, and it cannot be used with transitive verbs. It does, however, seem fairly productive with (potential) unergative verbs, which would be in line with this prediction. Further research is needed to determine whether there are any semantic differences between causatives of change of state verbs that take -si and those that do not.29

In this section, I briefly discuss the following two properties of the Kipsigis system which have counterparts in other languages, and which are of theoretical interest: a) the moraic form of the verbalizer, and b) the connection of the verbalizer to argument structure (and more specifically, the causative alternation).

I have shown in this paper that Kipsigis has a little v head which is spelled out by an empty mora. While this may not seem strange for a Nilotic language, where moraic morphemes are common, what is interesting is that the same claim (i.e., that a “conjugation class” can be analyzed in terms of the presence of a little v head spelled out as an empty mora) has been made for Greek (Spyropoulos et al. 2015; Panagiotidis et al. 2017).30 A somewhat similar claim has also been made for Sinhala; Letterman (1997) argues that the language has two conjugation classes, where one class is marked by a theme vowel, while the other has an empty slot that is filled by epenthetic material. Finally, Lampitelli et al. (2021) argue that the thematic element of the first conjugation class in the Negrons dialect of Friulian has a moraic affix allomorph. These languages are unrelated, and it is probably not a coincidence that all of them feature a moraic morpheme with effects resembling those of a conjugation class. Thus, if this work is on the right track, an interesting topic for further research is why moraic material is preferred for verbalizing heads near the root.

In Kipsigis, the two (descriptively speaking) conjugation classes are clearly related to argument structure, and more specifically the causative alternation – a prototypical transitivity alternation. As has already been mentioned, Dimmendaal (1983) argues that most Nilotic languages have the Class I vs. Class II distinction, and he shows that historically it emerged from a Proto-Nilotic causative prefix *i. The Kalenjin dialects (which include Kipsigis) have maintained the causative nature of the distinction, but there seem to be two differences from Proto-Nilotic; first, the verbalizer now has the form of a mora, and not invariably an i-, and second, there are Class II verbs without causative semantics (the non-alternating verbs, which are root-merging in my analysis). Dimmendaal (1983) argues that the distinction has been mostly lost in Western Nilotic (and the Eastern Nilotic language Bari) which have developed prosodic classes instead, while it is purely morphological in Eastern Nilotic, where verbs do not generally alternate between the two classes.31 Therefore, what we see is that while Proto-Nilotic had a causative morpheme, Kalenjin dialects have moved to a stage where this morpheme can also be used as a verbal marker without causative semantics (non-alternating verbs), and Eastern Nilotic languages now only use it as a verbal marker. The variation within Nilotic can, therefore, shed light on theories of the historical evolution of conjugation classes and theme vowels, and can help explain the common observation that there is a correlation (but not a one-to-one relationship) between transitivity and conjugation classes in many languages (e.g., Armenian, Dolatian & Guekguezian 2021). This is reminscent of the well-known correlation between declension class and gender in the nominal domain, and is an obvious topic for further research.

In this section, I first provide a brief discussion of declension classes in Kipsigis, before comparing to the verbal domain and discussing a potential typological asymmetry between verbs and nouns.

Kipsigis nouns follow a tripartite system of number marking: some nouns are unmarked in the singular and form their plural with a plural suffix (inherently singular nouns), some are unmarked in the plural and form their singular with a singulative suffix (inherently plural nouns), while a third class forms its singular with a singulative and its plural with a plural (numberless nouns). Irrespective of number class, nouns in the language generally have the following template (Kouneli 2019; 2021c):

The thematic suffix usually consists of either a vowel or a glide + vowel combination. If a number (plural or singulative) suffix is present, the thematic suffix is determined by the number suffix; if a number suffix is absent, the thematic suffix is determined by the root. Representative examples are provided in (37)–(38), where the form to the left of the arrow shows the morphological make-up of the noun and the form to the right of the arrow shows the surface form, after regular phonological processes have taken place.

In Kouneli (2021c), I show that Kipsigis thematic suffixes bear striking similarities to Romance theme vowels in the nominal domain (e.g., Roca 1989; Aronoff 1994; Alexiadou & Müller 2008; Oltra-Massuet 1999; 2020). First, they are usually vocalic elements, as was already mentioned.33 Second, they cannot be predicted by the semantic content or phonological shape of the root (or number affix). Third, they do not have semantic content of their own and do not play any role in the syntax. Finally, the language has a variety of plural affixes, and the choice of plural affix (partially) depends on the thematic suffix that a noun has in the singular (e.g., nouns with an -i theme vowel take the -iːs plural suffix). This indicates that thematic suffixes are associated with declension class in the language.34

Due to these similarities to Romance theme vowels, in Kouneli (2021c) I extend Oltra-Massuet & Arregi’s (2005) analysis of Spanish theme vowels to Kipsigis. I argue that theme nodes are added postsyntactically (as dissociated nodes) to each functional head in the DP, but only one theme node is pronounced. For Spanish, Oltra-Massuet & Arregi (2005) argue that the theme node that is pronounced is the highest one below Num. In Kouneli (2021c) I argue that in Kipsigis, it is the theme node attached to Num that is spelled out instead (thematic suffixes follow the number suffix in Kipsigis, but precede it in Spanish). I therefore conclude that there is cross-linguistic variation in the choice of the theme node that is pronounced.35

There are at least eight different thematic suffixes in Kipsigis (-a, -o, -i, -u, -e, -wa, -ja, ∅) and the number could be even higher if tone is also taken into account (most thematic suffixes come in H- and L-toned counterparts). Furthermore, they cannot be easily associated with a projection in the DP, which is why I opt for an analysis in terms of dissociated nodes added post-syntactically in Kouneli (2021c). The situation in the nominal domain is, therefore, very different from the verbal domain. In the latter, there is no need for conjugation class features or dissociated nodes, since Class II can be reduced to the presence of a little v spelled out as a mora. There is therefore an asymmetry between nouns and verbs: nouns have declension classes and theme vowels, while verbs have neither.

Interestingly, we find a similar pattern in Greek, an unrelated language. As has already been mentioned at various points, Spyropoulos et al. (2015) and Panagiotidis et al. (2017) argue that the second conjugation class can be explained away if we assume the presence of an empty vocalic slot. Even if one maintains the traditional description, Greek would have two conjugation classes in the verbal domain, while there are eight declension classes in the nominal domain (e.g., Ralli 2000; Alexiadou Müller 2008). Similarly, Barillot et al. (2018) have shown that Somali (Cushitic), yet another unrelated language, does not really have conjugation classes in the verbal domain, with differences in inflection being reducible to regular phonology; the same cannot be done for the nominal domain, where it is usually assumed that nouns come in various classes.

We therefore have (at least) three languages with various declension classes in the nominal domain, but few or no conjugation classes in the verbal domain. I am not aware of a language with the reverse pattern: no declension classes (and/or theme vowels) in the nominal domain, but many conjugation classes in the verbal domain. However, this statement needs to be evaluated in a proper typological study, which is beyond the scope of this paper. I do note that data from European languages seem consistent with the observation that nouns have more classes than verbs. Whether the pattern holds in a given language partly depends on how one counts classes, but in Spanish (and other Romance), for example, we usually find three verbal classes, but four theme vowels for nouns; in Lithuanian, we find four (major) classes for nouns, but three for verbs (Yuriy Kushnir, p.c.). While the asymmetries here are not as significant as in the Greek or Kipsigis case, they are in the same general direction of nouns showing more distinctions than verbs.

It is generally acknowledged that there are category-specific phonological effects (Bobaljik 2008; Smith 2011; Hyman 2019: e.g.,). In an overview of the documented patterns, Smith (2011) observes that in most cases, nouns show more phonological distinctions than verbs, which would be in line with the observations made here regarding morphological classes. It is therefore an interesting topic for further research whether the generalization that nouns have more inflectional classes than verbs is robust typologically, and if so, how our theory of lexical categories can account for it.