Re-placing PStem in the prosodic hierarchy

3.1 PStem distinct from PWord

In prosodic structure theory, a considerable body of work has argued, following Inkelas (1989, 1993), for a PStem-PWord distinction in the Prosodic Hierarchy, based on a cross-linguistically diverse set of languages, including many of those referenced in Section 2, above. The default definition of PStem that we adopt is based on Bermudez-Otéro’s (2017: 105) definition of stem; recall that prosodic constituents by default match a morphosyntactically-defined constituent:

We follow Bermudez-Otéro (2017) in proposing that the stem, unlike the word, need not be fully inflected, as it need not parse all of the affixes to the lexical root. That is, the PStem canonically parses derivational affixes but not inflectional ones. As a result, PStem is not necessarily either prosodically or syntactically autonomous. Because PStem does not necessarily parse a free form, it follows that it is also not necessarily subject to minimality. While PStem by default matches the morphosyntactic constituent defined by the Root plus derivational affixes, Section 2 shows that mismatches are common. For example, the prefix-suffix asymmetry schematized in (2), above, defines the PStem as the Root plus all following suffixes, whether they are derivational or inflectional.

PWord by default matches a lexical word as defined by Bermudez-Otéro (2017: 105):

Since PWord, unlike PStem, by default matches an autonomous, fully inflected lexical item, it is canonically, in the sense of Corbett (2007), subject to minimality. (See McCarthy and Prince (1986) and much subsequent work establishing that minimality is cross-linguistically a canonical property of the PWord domain.^[5]) The schema below, chosen for the sake of concreteness, illustrates the prosodic parse that would be given to (2), above:^[6]

While PWord by default matches the syntactic or lexical word, mismatches are well-attested in the prosodic structure theory literature. For example, many languages impose a disyllabic minimality condition on PWords, which is actively satisfied by augmenting a subminimal lexical word through, e.g., epenthesis (V) to provide an additional syllable: (_PwordV [_word CV]). We will see an example of augmentation via epenthesis to satisfy PWord minimality in the discussion of Shona in Section 4.1, below.

To conclude, since PStem, like PWord, is by default morphosyntactically-defined, it satisfies prosodic structure theory’s “explanatory goal – minimally, a motivated identification of categories across languages, such that the [default] ‘xyz-[prosodic constituent]’ of one language can be confidently equated with the [default] ‘XYZ-[prosodic constituent]’ of another […]” (Ito and Mester 2009a: 228). Just as importantly, the PStem-PWord distinction allows us to straightforwardly model the cross-linguistically robust generalization concerning a stem-word asymmetry defining domains of lexical phonological processes motivated in Section 2.

3.2 Recursive PWord replaces PStem-PWord distinction?

Even though parsing the stem domain as PStem has clear advantages, it does add a constituent to the Prosodic Hierarchy. To keep the repertory of prosodic constituents as parsimonious as possible, PWord recursion has been proposed in work like Bennett (2018), Booij (1996), Booij and Rubach (1984, 1987), and van der Hulst (2010) as a way to model a distinction between stem level (‘cohering’; low level) and word level (‘non-cohering’; high level) affixes.^[7] This is schematized in (6), which shows how non-cohering prefixes are parsed into a recursive PWord with their base in these analyses:

Although PWord recursion has come to be widely accepted, there are reasons to be dissatisfied with this approach as a general alternative way to formalize a stem-word asymmetry.^[8] As noted above, a principal advantage of proposing a PStem constituent distinct from PWord is that this provides the most straightforward way, within prosodic structure theory, of formalizing the stem-word asymmetry which Kiparsky (2000) proposes is universal. Collapsing this distinction in favor of PWord alone fails to capture the generalization that it is cross-linguistically very common for languages to have two lexical (subphrasal) domains, with distinct phonological properties. Further, if prosodic constituents by default match their morphosyntactic correlates, then excluding classes of affixes from the PWord domain, as in (6) above, obviously has the potential to create a considerable mismatch between PWord and the corresponding grammatical word, making it difficult to identify unifying cross-linguistic morphosyntactic properties of PWord. Finally, since PStems are bound, they need not be subject to minimality constraints, whereas PWord canonically is subject to minimality. If PStem is replaced by PWord, it is unclear how a cross-linguistic generalization concerning domains subject to minimality could be formalized, further diminishing the unifying cross-linguistic properties of PWord. (See Inkelas 1989 and Downing 1999 for detailed development of arguments like these.)

An additional problem with PWord recursion is that it violates a markedness constraint holding of well-formed prosodic constituent structures, NoRecursivity (Selkirk 1995: 443). As recent work by Frota and Vigário (2013), Guzzo (2018), Vigário (2010), and Vogel (2009a, 2009b, 2010, 2012, 2019) forcefully argues, even though this constraint, like others in an Optimality Theoretical approach, can be optimally violated to satisfy higher-ranked prosodic well-formedness constraints, a recursive representation must still strictly satisfy well-formedness criteria holding for linguistic recursion in general. In particular, recursion should involve “embedding a constituent in a constituent of the same type” (Pinker and Jackendoff 2005: 211, cited by Vogel 2012). For this requirement to be met, prosodic recursion must satisfy the criteria in (7):

In the literature on PWord recursion, one finds analyses that meet at least one of these two criteria: see, e.g., Bennett (2018), Guzzo (2018), Vigário (2010), and Zec (2005). However, work like Bickel et al. (2009), Frota and Vigário (2013), Guzzo (2018), Schiering et al. (2010), Vigário (2010), and Vogel (2009a, 2009b; 2010, 2012, 2018, 2019) show that many analyses involving PWord recursion are not well formed according to (7), above. The same phonological processes or constraints do not apply to the outer recursion of PWord as to the inner recursion. Indeed, the motivation for a stem-word asymmetry in all of the cases summarized in Section 2 is precisely that stem and word domains do not have the same phonological properties. Processes or constraints that target the stem domain do not apply to the entire word. And conversely, there are processes that apply differently in the word domain than in the stem domain.

A final conceptual problem with recursion is that, as Schiering et al. (2010: 699) argue, if an unlimited number of intermediate recursions of, for example, PWord, is allowed by a theory, it makes prosodic recursion “too powerful and puts too [few] restrictions on prosodic systems,” since intermediate prosodic recursions can parse morphosyntactic groupings defined by language-particular morphosyntactic structures rather than constituents with cross-linguistic validity. As van der Hulst (2010: 326) observes, though, it does not appear that languages need to appeal to more than two recursions of PWord (or any other prosodic constituent). Note that two recursions of PWord define exactly three subphrasal constituents, precisely as schematized in (1), except that the three constituents in (1) crucially are distinct in kind, not recursions of another constituent. A limitation to three subphrasal constituents is, though, a stipulation in most work appealing to PWord recursion.

3.3 Composite Group (CG)-PWord distinction replaces PWord-PStem distinction?

Another alternative to PStem has been argued for in work by Vogel (2009a, 2019b) and Vigário (2010: fn 21, fn 26), also invoking parsimony. They propose that the range of facts supporting a PStem versus PWord distinction can be re-analyzed as a PWord versus Composite Group (CG or equivalent) distinction. Vogel (2019: 34) provides the following informal definition of CG:^[9]

This definition must be considered a proposal for the default parse of the CG, since it is well-established that in some languages, certain clitics are arguably parsed within their host PWord, not external to PWord (in CG, for example). (See, e.g., Inkelas (1993), Zec and Inkelas (1992), Kaisse (1983), Peperkamp (1996), Selkirk (1995), Vigário (2010), and Zec (2005) for discussion and exemplification.) That is, for CG, as for other prosodic constituents, one expects to find mismatches between the morphosyntactically-defined default domain and the phonologically-motivated domain in a particular language.

Vogel’s (2009a, 2009b) and Vigário’s (2010: fn 21, fn 26) reanalyses of PStem are not worked out in detail, but one assumes the proposal would be that the structure in (2) would have the prosodic parse given in (9):

The representation in (9) faces a number of problems, though. First, stem-external affixes do not necessarily have properties that motivate parsing them outside the PWord. On the contrary, much of the literature motivating the stem-word asymmetry cited in Section 2 demonstrates that affixes parsed into the (P)Word outside of (P)Stem are included with the (P)Stem for some word-bound processes. The representation in (9) thus misses the generalization that it is cross-linguistically common for a language to have two sets of bound affixes that define distinct domains for word-internal processes.

Further, this approach shares problems with the recursive PWord approach. If prosodic constituents by default match their morphosyntactically-defined correlates, then excluding classes of affixes from the PWord domain, as in (9), obviously has the potential to create a considerable mismatch between PWord and the corresponding grammatical word, making it difficult to identify unifying cross-linguistic properties of PWord. Finally, since PStems are bound, they need not be subject to minimality constraints, whereas PWord canonically is subject to minimality. If PStem is replaced by PWord, it is unclear how this cross-linguistic generalization could be formalized, further diminishing the unifying cross-linguistic properties of PWord.

Finally, because this approach parses PWord-external (less cohering) affixes together with clitics or function words outside the PWord domain, it predicts that PWord-external affixes and clitics/function words should have the same phonology. One does find analyses supporting this prediction, and, as Vigário (2010: 494) notes, a common pattern is for proclitics to pattern with prefixes in being less cohering, whereas enclitics pattern with suffixes in being parsed into PWord.^[10] However, Bermudez-Otéro (2011) provides a counterexample to this prediction from English. It is well-established that English has a distinction between stem level affixes and word-level affixes. In a model which assumes the two subphrasal levels, CG and PWord, this distinction would most straightforwardly be formalized by parsing stem-level affixes into PWord and word-level affixes into the CG, external to PWord. English also has function word clitics, both proclitics and enclitics. These are plausibly parsed into CG together with word level affixes in the CG-PWord model. As Bermudez-Otéro (2011: 10) argues, parsing both word level affixes and enclitics into the same prosodic domain makes the prediction that phonological processes like the English process of /l/-darkening should apply the same way before a word level suffix like -ing as before an enclitic. Hayes (2000: 98) shows, however, that /l/-darkening applies with greater frequency before an enclitic (heal it) than before a word level suffix (heal-ing). As Bermudez-Otéro (2011) concludes, these two forms must have distinct prosodic representations in order to account for these facts. A CG-PWord model of subphrasal prosodic representations does not offer sufficient distinctions. The case studies of Limbu and Shona presented in Section 4 emphasize this point.

Before concluding this section, it is important to highlight that even though a CG-PWord distinction cannot systematically replace a PWord-PStem distinction, there is ample other evidence for a CG-PWord distinction, based mainly on the phonology of clitics and compounds. It is beyond the scope of this paper to present these arguments in detail, and the interested reader is urged to consult work like Guzzo (2018), Vigário (2010), and Vogel (2009a, 2009b; 2010, 2012, 2018, 2019) for detailed discussion. We simply note that many of the arguments given in these works for why PWord recursion cannot replace a CG-PWord distinction are analogous to those presented in Section 3.2 for why PWord recursion cannot replace a PWord-PStem distinction.

4.1 Shona

Shona (Guthrie number S.11–15) is a Bantu language spoken mainly in Zimbabwe and Botswana. Like most other Central Bantu languages, verb words exhibit the prefix-suffix asymmetry that Hyman (2008) argues often correlates with the stem-word asymmetry schematized in (2), above. The structure of the Shona verb word is given in (11), below, based on discussion in Myers (1987, 1998):

A distinction between (P)Stem versus (P)Word domain for phonological processes in Shona is well-established from previous work on the language, as several phonological processes distinguish the two domains.^[12] As is typical for Bantu languages (Hyman 2008), the PStem is the domain for vowel harmony (Beckman 1997) and forms the base for reduplication (Odden 1981). Three additional processes motivating a PStem-PWord asymmetry are discussed in turn in this section: minimality, Meeussen’s Rule (an OCP-motivated constraint on High tone realization) and vowel hiatus resolution.

Minimality is a property of verb words in the Zezuru and Ikalanga dialects of Shona, as demonstrated in detail by Myers (1987, 1995) and Mudzingwa (2010). Subminimal words are augmented through the epenthesis of morphologically empty material. This is illustrated by the imperative forms in (12), below. The forms in (12e–g) show that in minimally disyllabic stems, the bare stem forms the imperative. The imperative forms in (12a–d) show that subminimal (monosyllabic) verb stems are augmented by epenthesizing i-, creating a mismatch between the grammatical word and PWord:

This data shows not only that PWords are subject to a minimality constraint, but also that prefixes like the infinitive prefix ku-, when present, can satisfy that constraint. Hence, prefixes must be parsed with the stems into PWord.^[13] However, stems themselves are obviously not subject to a minimality constraint, as they are only augmented when they occur as independent PWords, in the imperative.

Further evidence for a stem-word distinction comes from the OCP-motivated tonal process, Meeussen’s Rule, as Myers (1987, 1995, 1997, 1998) demonstrates in some detail. (Meeussen’s Rule deletes the second in a sequence of High tones.^[14]) Myers shows that while Meeussen’s Rule is a word-bound process, its application is morphologically-conditioned within words: it systematically applies across a stem boundary, as shown in (13a–c). However, Meeussen’s Rule systematically fails to apply within the string of prefixes which precedes the stem, as shown in (13d–e):

Formalizing the stem-word asymmetry in terms of PStem and PWord allows Meeussen’s Rule to be defined as a domain juncture process (Selkirk 1986; Vogel 2009a, 2009b, 2010, 2019), which applies across prosodic constituent edges.

Finally, Myers (1987) and Mudzingwa (2010) demonstrate in careful detail that vowel hiatus is resolved differently across stem boundaries than within the prefix string.^[15] The data in (14d–g) show that in a hiatus context created by a subject prefix followed by a vowel-initial prefix, the vowel of the subject prefix undergoes resyllabification with a following prefix (deletes or glides). However, if the next vowel is stem-initial, a homorganic glide is inserted before the second vowel. The different resolution of the i-o sequences in (14c) versus (14d) highlights the importance of the stem juncture in conditioning the hiatus resolution strategy:

It is important to note that, as Myers (1987: 232) and Mudzingwa (2010) show, vowel hiatus is not resolved – either by glide epenthesis or resyllabification – across word boundaries. That is, hiatus resolution is a word-bound process:

The generalization that emerges is that glide epenthesis, like Meeussen’s Rule, is a word-internal domain juncture phenomenon. When no word-internal prosodic constituent boundary – e.g., PStem – separates vowels in hiatus, other resolution processes apply.

There are several reasons why one cannot plausibly recast the PStem-PWord distinction motivated by these processes in terms of PWord recursion:

PStems are not subject to minimality, even though, in a recursion analysis, the equivalent of PStem would be a (minimal) PWord, a constituent that canonically is expected to be subject to minimality. Further, as we have seen, Meeussen’s Rule and vowel hiatus processes apply differently within the prefix string than across the prefix-stem boundary. This contradicts the definition of recursion in (7): phonological processes should apply recursively and uniformly within recursive phonological domains.

Contra Vigário (2010: fn 21, fn 26) and Vogel (2009a, 2009b) the PStem-PWord distinction in Bantu languages like Shona also cannot easily be recast as a CG-PWord distinction:

It is unclear why it would follow, in this approach that CG must, cross-linguistically, satisfy minimality while PWord does not. PWord is canonically expected to be a domain that is subject to minimality. Further, parsing prefixes as if they were clitics, external to the PWord, incorrectly suggests that prefixes should be excluded from word-bound phonological processes. As Myers (1987, 1995, 1998) demonstrates, prefixes participate in prosodic processes which are PWord-bound, like tone spread and the calculation of minimal word.

An additional problem with parsing prefixes as if they were clitics in Shona (i.e., in CG, external to PWord; see (17)) comes from differences in the phonological behavior of prefixes and clitics for minimality, Meeussen’s Rule and vowel hiatus resolution. Prefixes contribute to the satisfaction of word minimality, as shown in (12), above. However, clitics do not. As Myers (1987) demonstrates, the augmented form of the imperative of monosyllabic stems is maintained when certain enclitics are added to them (cf. (12)):

These forms provide further evidence for PWord, since one must specify a minimal PWord as the base for cliticization. And they demonstrate the distinction between a PWord and a CG domain, since only morphemes parsed in the PWord domain satisfy minimality.

The application of Meeussen’s Rule provides additional evidence that prefixes and proclitics are parsed in distinct prosodic domains. (See Myers (1987, 1998) for detailed discussion.) A clitic triggers Meeussen’s Rule on a following High-toned prefix, (19), or enclitic, (20). In contrast, recall from (13), above, that a High-toned prefix does not trigger Meeussen’s Rule on a following High-toned prefix:

Finally, note in (19c) that a proclitic does not trigger elision of a following vowel-initial prefix, whereas prefixes do. (See (14), above.) And monosyllabic enclitics are subject to glide epenthesis, unlike affixes, as shown in (20). (See Mudzingwa 2010: 76–77 for discussion.) These distinctions in the phonological properties of affixes and clitics obviously are problematic for a CG-PWord analysis, as it would parse prefixes and all clitics together in CG outside of PWord.

We propose that the most straightforward way to account for these contrasts in the phonological behavior of clitics and inflectional prefixes is to appeal to a distinction between PWord, which parses prefixes into a constituent external to PStem, and CG, which parses clitics into a constituent external to PWord:

Meeussen’s Rule and glide epenthesis can then be analyzed as domain juncture processes that take CG as their domain.

4.2 Limbu

Limbu is a Sino-Tibetan language of Nepal. Bickel et al. (2009), Hildebrandt (2007), and Schiering et al. (2010) analyze the phonology of Limbu as their parade example in arguing that the traditional Prosodic Hierarchy does not provide sufficient subphrasal prosodic constituents to account for all the phonological domains that are cross-linguistically well-attested in what they define as a prefix-stem-suffix=clitic string. (See this work for detailed motivation of the suffix-clitic distinction in Limbu.) In this section, we show that the proposed expanded Prosodic Hierarchy in (10) neatly accounts for the domains motivated for Limbu by general phonological processes of the language.^[16]

First, as they show, Limbu, like Shona, has the kind of prefix-suffix asymmetry that Hyman (2008) argues cross-linguistically correlates with a stem-word asymmetry: several phonological processes that apply within the stem domain, defined as [stem-suffix=enclitic], fail to apply to prefixes. For example, Hildebrandt (2007) establishes that an l∼r alternation (l is realized as r if it occurs intervocalically or after a glottal stop and preceding a vowel) applies systematically across stem-internal morpheme boundaries but fails to apply if the first vowel is in a prefix:

Prefixes are also outside the domain of stress assignment. As shown in the examples below, the stem-initial syllable is assigned main stress (and secondary stress is assigned to non-initial, stem-internal bimoraic syllables). Prefixes are not stressed unless they must be recruited to satisfy a disyllabic minimality condition on footing (see Bickel et al. 2009, Hildebrandt 2007, and Schiering et al. 2010 for discussion):

Finally, different vowel hiatus resolution strategies apply at the prefix-stem juncture than stem-internally.^[17] Vowel sequences can occur stem-internally, and are analyzed as diphthongs in Schiering et al. (2010). However, at the prefix-stem juncture, such diphthongal vowel sequences are never found. All stems (and words) must begin with a consonant, and Schiering et al. (2010) posit that stem-initial and word-initial glottal stops occur to satisfy this constraint:

The prefix-suffix/enclitic asymmetry motivated by this data clearly illustrates Hyman’s (2008) stem-word asymmetry in (2), and it can easily be modeled in prosodic structure theory as a PStem-PWord distinction. That is, the [stem-suffix=enclitic] string is parsed as PStem, while the prefixes are parsed outside of PStem, into PWord:

Because some phonological processes apply to PStem, excluding prefixes, recursive PWord is not a satisfactory alternative parse to the one in (25), for reasons taken up in detail in Section 3.2, above.

In fact, Schiering et al. (2010) acknowledge that the [stem-suffix=enclitic] domain could potentially be parsed as PStem. Their main argument against this analysis is that enclitics are syntactically phrasal elements and therefore not plausibly prosodified into a sub-phrasal prosodic constituent. However, phrasal clitics are actually quite commonly prosodified within a subphrasal prosodic constituent. For example, enclitics such as reduced auxiliaries in English (e.g., =s for is or has) are also clearly syntactic elements, yet they arguably prosodify into PWord, since they undergo the same word-bound phonological processes as phonologically identical suffixes do. (See, e.g., Kaisse 1983, Selkirk 1995 for discussion.)

Positive empirical motivation for parsing prefixes into a PWord domain with PStem in Limbu is provided by the process of labial assimilation (coronal stops and nasals assimilate in place to a following labial consonant). As shown by the following data, this process can apply across any morpheme boundary, including the prefix-stem boundary:

Because labial assimilation applies to both prefixes and stems, it is not plausible to parse prefixes into CG, external to PWord, as in (27):

This parse fails to formalize the generalization that prefixes are affected by word-bound phonological processes.

Hildebrandt’s (2007) discussion of the phonology of nominal compounds provides additional empirical evidence that labial assimilation applies within the PWord domain, not the CG domain. As Hildebrandt shows, the members of nominal compounds must be parsed into distinct prosodic domains to account for the fact that labial assimilation – a process that we have just seen applies across all PWord internal morpheme boundaries – does not apply across the members of a compound. The l∼r alternation illustrated in (22), above, also fails to apply across a nominal compound boundary, as we would expect since it applies only within PStem:

We conclude that Limbu nominal compounds are two-domain compounds: prosodically separate domains, even though they show the syntactic and semantic cohesion which define compounds as single lexical words.^[18] To formalize this generalization, we propose, following work like Vigário (2010) and Vogel (2010, 2012, 2018, 2019), that each member of the compound is parsed into PWord. This accounts for the fact that labial assimilation, a PWord-bound process, does not apply across members of the compound. The entire compound is parsed into CG (8):

If prefixes were parsed into CG, as in (27), it would be impossible to account for why labial assimilation applies across prefix-stem boundaries, but not across members of a compound. If labial assimilation applies across a PWord boundary following a prefix, all things being equal, it should also apply across a PWord boundary following the first member of a compound. Another alternative analysis is to parse the compound into recursive PWords, as schematized in (30), below:

This parse would face the usual problems posed for PWord recursion by two-domain compounds, which are discussed at length in Vigário (2010) and Vogel (2010, 2012, 2018, 2019). Labial assimilation is blocked between members of a compound, even though each recursion should have the same phonological properties in order to satisfy the well-formedness criteria holding of recursion in (2).

To sum up, Bickel et al. (2009), Hildebrandt (2007), and Schiering et al. (2010) demonstrate that Limbu phonology provides evidence for three subphrasal prosodic constituents, as schematized in (31):

All three are needed to account for the distinct phonological behavior of prefixes vs. suffixes and enclitics, as well as the phonology of Limbu’s two-domain nominal compounds.