Recent years have witnessed intensive research on so-called *ABA patterns—cross-linguistic patterns whereby, given a particular arrangement of forms in a certain type of paradigm, the first and third form may share some morphological property “A” only if the second form also shares property “A” (see Bobaljik 2012 and much related work). One such pattern has recently been discussed by Smith et al. (2018), who propose (1) as a universal *ABA restriction on the distribution of root allomorphs in case-sensitive suppletion.

Following Bobaljik (2012), whose logic I review in detail in Section 2, Smith et al. (2018) interpret (1) as evidence for a universal containment hierarchy like (2), such that the representation of every inherent case must contain that of a marked core case, which latter must in turn contain the representation of an unmarked core case.

Given some ancillary assumptions, a simple approach to syncretism—in terms of missing dedicated exponents “filled in for” by their closest match—predicts that the containment hierarchy in (2) should then constrain possible case syncretisms, too. This is because, absent a dedicated affix for an inherent case, (2) will always ensure that the accusative/ergative affix be a closer match for that inherent case than the unmarked-case affix would be. In this paper, I argue that this prediction is indeed borne out, and I defend the ensuing generalization in (3)—with important antecedents in Baerman, Brown & Corbett (2005) and Caha (2009)—against a sample of 102 case-inflecting languages.

Having established that case-conditioned suppletion and case syncretism really obey the same *ABA restrictions, I move on to use those restrictions as a probe into the structure and nature of case categories. I show, more specifically, that *ABA consistently partitions cases into classes, and that those classes are rigidly ordered relative to each other, but are internally unordered or not fully ordered. In particular, ergative and accusative make up an internally-unordered class of their own, and so do inherent cases, while the genitive appears not to be constrained by the hierarchy at all, syncretizing freely in defiance of any universal restriction. Such a partition can be made sense of under an approach to case syntax that puts ergative and accusative in the same natural class to the exclusion of inherent cases, while casting the genitive on a different plane. These desiderata, I shall argue, are only met by Marantz’s (1991) and Baker’s (2015) theory of dependent case (cf. also Yip, Maling & Jackendoff 1987), which thereby receives a new kind of empirical support.

Finally, I conclude my discussion by examining how the core results in the paper may be derived from the relevant containment hierarchy under different views of the syntax–morphology interface than the one, simply based on underspecified exponents, which I assume in Sections 2–3. I focus, in particular, on variants of Distributed Morphology that countenance feature-deleting operations between Narrow Syntax and exponence, and on overspecification-based alternatives falling under the rubric of Nanosyntax. The key empirical results will turn out to be in principle compatible with versions of both frameworks, albeit with different analytical tradeoffs.

Smith et al. (2018) carry out a wide cross-linguistic survey of case-sensitive suppletion in pronouns.1 For comparative purposes, they restrict their focus to a simplified typology of cases, comprised of the core structural cases and “a representative oblique case, typically the dative” (Smith et al. 2018: 11). Importantly, they set genitives aside, as their sources do not consistently distinguish them from possessive pronouns (which they assume are not part of the relevant paradigm). Smith et al. (2018) examine 179 languages, 41 of which have case-conditioned suppletion and more than two cases (genitives aside). This sample supports the generalizations in (4) and (5) regarding nominative–accusative and ergative–absolutive systems, respectively.

Given the sequences NOM ≺ ACC ≺ OBL and ABS ≺ ERG ≺ OBL, we may thus find AAA (no suppletion), AAB (only the core structural cases sharing the same stem), and ABB (only accusative/ergative and oblique sharing the same stem), but we never find ABA (cf. Tables 1–2).2

McFadden (2018) provides further evidence for this pattern in a survey of case-sensitive stem allomorphy in lexical nouns. In that work, “[t]he term ‘stem’ is used to contrast with root suppletion (as found in go/went), and to indicate that the allomorphy involves part of the base to which case attaches rather than the case suffix itself” (McFadden 2018: 4). Of interest, in other words, are alternations like Tamil maram ~ maratt- or Latin iter ~ itiner- in Table 3. McFadden analyzes such alternations as case-conditioned allomorphy of the stem’s last formative, which he identifies with the categorizing head n. In the Tamil paradigm in Table 3, for example, McFadden assumes that n is spelled out as -am in the nominative but as -att- in all other cases. Table 3 shows that ABB and AAB patterns are again possible in this domain. By contrast, ABA patterns are unattested.3

Following Bobaljik’s (2012) analysis of *ABA in comparatives and superlatives, all these *ABA generalizations can be taken as evidence for successive containment relations between the case categories involved in each:

One possible way to implement this, entertained besides other alternatives by Smith et al. (2018), is in terms of superset–subset relations between complex feature bundles, as illustrated in (7).4

These representations straightforwardly permit us to derive *ABA within a framework like Distributed Morphology, in which syntactic nodes undergo late insertion, proceeding from the most deeply embedded node outwards (Halle & Marantz 1993; Bobaljik 2000). In such a framework, suppletion is captured by positing multiple rules of exponence for the same terminal node, and which rule applies to which occurrence of that node is determined by principles (8)–(9).

Assuming this background, together with the containment relations in (6)–(7), we can show what blocks ABA patterns by trying to derive one—for example, pseudo-Georgian ABS is ~ ERG ma-n ~ DAT **is-s(a).

In order to surface only in the marked ergative case, the allomorph ma- has to be explicitly restricted to that context in its rule of exponence (10a). In DM, ma- is thus not eligible for realizing 3SG in the absolutive, since that context does not contain an ERG feature or head, and hence does not match ma-’s structural description. By contrast, underspecified is does qualify as a competitor for realizing 3SG both in the absolutive and in the ergative, but is not selected for the latter because the Elsewhere Principle favors the more specific allomorph ma- there. For the dative, however, we can only do one of two things: either say no more about it or stipulate a third exponence rule specifically for it. In the latter scenario, we end up with a disuppletive pattern ABC.5 In the former, assuming no exponence rules other than (10), the two allomorphs is and ma- should then compete to realize the pronoun in the dative, under the assumption that the dative contains ERG; but then the Elsewhere Principle should let the more specific ma- win again, resulting in ABB. The unattested ABA pattern is thus excluded in principle.

The assumption of a case containment hierarchy also has the potential to interact in interesting ways with a restrictive approach to syncretism, as was noticed, in partly different theoretical contexts, by Johnston (1996) and Caha (2009). Let us assume, more specifically, that syncretism may only result from the absence of a dedicated rule of exponence for a particular feature bundle—a gap which the vocabulary-insertion algorithm “fills in” by resorting to the closest underspecified exponent, as per the Elsewhere Principle (9). If this approach is on the right track, and if the case containment hierarchies in (6)–(7) are real, then we predict that the same *ABA pattern as we have witnessed for case-conditioned suppletion should also hold of case syncretism. In other words, just as a nominative and an oblique cannot share the same stem exponent to the exclusion of a suppletive accusative/ergative, so a nominative and an oblique should never share the same case exponent to the exclusion of a non-syncretic accusative/ergative.

To see why this should be so, we just have to replicate the reasoning from Section 2, and try to derive the supposedly impossible ABA syncretism by leaving DAT without a dedicated exponent.

Given that both NOM and ACC are properly contained in DAT, they will both be eligible candidates for realizing DAT according to Underspecification (8). However, since NOM is itself properly contained in ACC, ACC will always be a better match for DAT as per the Elsewhere Principle (9), thus necessarily resulting in ABB.

We thus derive the new generalization in (12)—with major precursors in Baerman, Brown & Corbett (2005) and Caha (2009), both to be discussed shortly.

As the alert reader may have noticed, the generalization in (12) specifically refers to non-accidental syncretisms—a term which I have not introduced yet. This qualification alludes to the fact that the reasoning schematized in (11) only rules out ABA patterns in genuinely morphosyntactic syncretism, i.e. syncretism which results from the application of the same rule of exponence to partially overlapping feature bundles. By contrast, the reasoning in (11) does not entail any analogous *ABA restrictions on other conceivable kinds of syncretism, whereby distinct morphosyntactic representations just accidentally happen to be realized alike.

Indeed, typologists such as Baerman, Brown & Corbett (2005) already recognized something akin to (12) as a cross-linguistic tendency, but refrained from treating it as a genuine language universal precisely because, short of a criterion for distinguishing such accidental homophonies from non-accidental syncretisms, they had no way to accommodate a number of reported surface counterexamples. This problem can be at least partly overcome, however, by the distinctive criteria proposed to this end by Johnston (1996) and Caha (2009), which I summarize in (13).

The rationale for (13b) deserves special emphasis. In Johnston’s (1996: 15) words, “[i]f we find that a suffix x in a certain context realizes properties a and b, it is entirely possible that the homonymy is accidental and of no more account than the two senses of bank in English. But if we find that in another context a suffix y also realizes properties a and b, then it becomes more likely that the homonymy is [non-accidental].” In line with this reasoning, (13b) rules out accidental homonymy whenever a syncretism is replicated by two or more phonologically different exponents across different inflectional classes.

Crucially, once we adopt the distinctive criteria in (13), we can then show that all the surface counterexamples to the *ABA generalization in (12) are actually accidental, and hence that (12) is, as stated, a solid contender for the status of an exceptionless universal.

Such a line of empirical defense, and indeed the generalization in (12) itself, have important antecedents in the work of Caha (2009), who also deployed the distinctive criteria in (13) to strengthen apparent cross-linguistic tendencies into putatively exceptionless restrictions on syncretisms. As it turns out, however, the empirical generalization he proposed, reported here in (14), is similar but not identical to the one in (12).

Specifically, Caha’s (2009) case containment hierarchy in (14) differs in two key respects from Smith et al.’s (2018) one in (6) (repeated here as (15)).

On the one hand, Caha’s hierarchy is richer (and hence more strongly predictive) than (15) in that it imposes a more articulated ordering on the various obliques—a move for which “the pronominal suppletion patterns provide no compelling evidence” (Bobaljik 2015: 9, fn8). On the other hand, Caha’s hierarchy is also less rich (and hence less predictive) than (15), in that it does not reference either ergative or absolutive, focusing on nominative–accusative systems instead (cf. Caha 2009: 10, fn5).

In the next sections, I will argue that Caha’s (2009) case hierarchy in (14) is actually inferior to the coarser hierarchy (15) on both counts, and that (15), originally proposed on the basis of restrictions on suppletion, is also the best fit for modeling universal restrictions on syncretism. As a first step toward this conclusion, I will show in Section 4 that the coarser hierarchy correctly constrains syncretisms not only in accusative systems but also in ergative ones, and that, in these latter, the ergative really mirrors the accusative’s behavior as the middle member in the *ABA pattern. In Section 5, I will then move on to argue that the case containment hierarchy is not subject to any linearity constraint. Rather, *ABA restrictions on both syncretism and suppletion consistently partition cases into classes, which are rigidly ordered relative to each other, but internally unordered or not fully ordered. A strict universal ordering of obliques as in (14) will thus be shown to undergenerate.

To test the empirical adequacy of the generalization in (12) (repeated in (16)) with respect to both accusative and ergative systems, I have put together the language samples used in four cross-linguistic studies of case syncretism: Plank (1991), Baerman, Brown & Corbett (2005), the Surrey Syncretism Database (Baerman, Brown & Corbett 2002)6 and Caha (2009: Part III). This has produced a total of 102 case-inflecting languages, 66 of which display partial case syncretism. A separate Appendix lists all of these languages, along with their respective syncretisms.

Within the sample I have collected, all the syncretisms that are clearly non-accidental in light of the criteria in (13) turn out to conform to (16). Examples from accusative and ergative systems are in Tables 4, 5, 6.

The survey has also turned up at most 8 surface counterexamples, of which:

I briefly discuss each of these cases in turn in Subsections 4.1–4.3.

Having established that the same *ABA pattern observed for case-sensitive suppletion also restricts possible syncretisms—in both accusative and ergative systems—we can now ask further questions about the structure and significance of the case hierarchies that both these phenomena point to.

One such question, for example, concerns the possibility of devising a unique case sequence valid for all languages, as was first suggested by Caha (2009) (cf. Section 3 above). An immediate issue for any such attempt is how to unify the nominative–accusative and absolutive–ergative variants of the hierarchy, both repeated in (17).

As it happens, this unification is required not just by usual considerations of simplicity and generality, but also by the empirical demands coming from tripartite languages, where the transitive subject (A), the direct object (O), and the intransitive subject (S) are each marked with a different case. If we want our account to also apply to such languages, we need a single hierarchy featuring both ergative and accusative at once.

However, neither of the linear arrangements in (18)—with UNMARKED as a tentative umbrella term for nominative and absolutive—is apparently compatible with the data provided by tripartite languages.

On the one hand, (18a) finds an ABA counterexample in the suppletion patterns of Jingulu, wherein nominative and ergative share the same stem to the exclusion of a uniquely suppletive accusative (Pensalfini 2003: 149–152). On the other hand, the alternative arrangement (18b) is also contradicted by an Australian suppletion pattern—this time the one of Alyawarra, in which the nominative patterns with the accusative to the exclusion of a suppletive ergative (Yallop 1977: 94).9 As it turns out, no linear arrangement based on (17) can be consistent with both Jingulu and Alyawarra at once.

The data in Tables 15–16 are not easily amenable to alternative accounts. First of all, we cannot invoke any such thing as “accidental suppletion” as we may want to do with homophony. Secondly, even if we could, each of the divergent patterns would turn out to be replicated by multiple stems in its respective language. Thirdly, the same problem arises with syncretism: in some tripartite languages, nominative and ergative syncretize to the exclusion of the accusative, while, in others, nominative and accusative syncretize to the exclusion of the ergative. Both of these patterns are far too widespread among and beyond Australian languages to be plausibly reducible to accidental homonymy (cf. Tables 17–18), and can even coexist within one and the same language, as in Djapu (cf. Table 19) and many other similar systems discussed by Blake (1977), Goddard (1982), and most recently Legate (2008; 2014).10

Even in these languages, however, it’s not that just anything goes. In fact, all the tripartite languages I know of still conform to the *ABA generalization in (12), as none of their syncretisms covers a nominative and an oblique without also covering either an ergative or an accusative. What these data suggest, then, is just that our unified case hierarchy should allow for some flexibility—namely, that it should be stated in terms of internally unordered (or at least not fully ordered) case-classes.

Analogous flexibility is also apparently required within the oblique class, pace Caha (2009). This is particularly evident in ergative and tripartite systems, given the wide variety of ergative–oblique syncretisms attested cross-linguistically: ERG–GEN and ERG–INSTR (the commonest two, respectively illustrated by Araona in Table 20 and Margany in Table 21), but also ergative–inessive in Lezgian (cf. Table 6) and still other locative patterns listed by Palancar (2009: 569). It turns out, in other words, that there is no one “lowest oblique” that the ergative universally favors when syncretizing “upwards.” Analogous variability, though perhaps less wide-ranging, is also observed for the accusative, which can syncretize with dative to the exclusion of instrumental in Classical Armenian, and with instrumental to the exclusion of dative in Latin (see Table 22). In conclusion, obliques too must be left (at least partially) unordered with respect to each other.

One last aspect of flexibility in the hierarchy specifically concerns the genitive, which seems to enjoy the highest degree of freedom among all cases, sometimes defying any generalization even within a single language family. Take for example the Germanic suppletion patterns in Table 23, in which the genitive displays ambiguous unmarked-like and oblique-like behavior. Once again, the same pattern (or, in this case, lack thereof) is also replicated in the domain of syncretism, as exemplified by Latin and Bilin in Tables 24–25.11

Evidently, the genitive’s variable behavior poses an especially hard challenge for the linear case hierarchy originally proposed by Caha (2009), repeated here in (20) (= (14) above).

Confronted with these challenges, Starke (2017) and Caha (2018b) attempt to salvage the contiguity hypothesis in (20) by enriching the case hierarchy further—specifically, by sandwiching the genitive between two ACC–DAT subsequences.

Such a proposal, however, both under- and overgenerates. On the one hand, it still does not explain how in Icelandic (a language which, according to Starke’s and Caha’s diagnostics, should only allow SMALL ACC and SMALL DAT to surface) the genitive can pattern with the nominative in suppletion (cf. honorific 1PL vér in Table 23). On the other hand, if a language could just use SMALL DAT and BIG ACC on its surface, it could then display the syncretism pattern NOM = DAT≠ACC, which we just never seem to find.

For these reasons, and in view of the broader pattern of obliques and marked core cases, I will thus reject any strict linearity constraint on the case hierarchy.12 I will instead defend a formulation in terms of three distinct case classes, and assume that the genitive is not a member of any of them.

Having established the case classes in (22) on morphological grounds, we may now take one more step and bring them to bear on the choice between competing theories of case syntax, asking which theory can best characterize such classes in natural terms.

A first challenge in this respect is how to fit into one class the various cases I have referred to as “obliques other than genitive,” such as dative, locative, and instrumental. The theoretical notion that best serves this purpose is that of “inherent cases.” These are cases assigned under strict locality with a selecting head, either as an instance of arbitrary selection or in response to the semantics of θ-role assignment. This fits the bill for the obliques we are interested in, but correctly excludes the genitive, which typically is not selected for, but rather serves as a default adnominal case.

A problem, however, might arise from the ergative, which should also be included in the inherent class according to some prominent accounts (see i.a. Woolford 1997; 2006; Laka 2006; Legate 2008; 2012; Mahajan 2012). On this view, ergative is inherently assigned by little v⁰ to its specifier, along with an external or “initiator” θ-role such as agent, experiencer, or instrument. A major attraction of this account is that it allows us to reconcile ergative–absolutive alignments with the Minimalist view of case in terms of feature checking, i.e. either strictly local selection or (potentially long-distance) Agree. Assuming that nominals which have already received case in the bottom-up derivation are no longer interveners for further Agree dependencies (Chomsky’s 2000 Activity Condition), we may then understand how T⁰ can skip the ergative subject in Figure 1, and assign absolutive to the direct object.

This account has recently faced several challenges, suggesting that the ergative does not behave syntactically as an inherent case. Inherent cases, for example, are generally exempt from structural case alternations, as is shown by the unalternating “quirky” datives in Icelandic raising to object (23). Ergative arguments, in contrast, frequently take part in such alternations, with no apparent change in θ-roles, as shown by Řezáč, Albizu & Etxepare (2014: 1280) for Basque raising to object (24).13

In accord with these findings, the current results from *ABA suggest that the ergative also does not behave morphologically like inherent cases. As we saw in Sections 2–3, inherent cases universally obey two *ABA generalizations: they can never be syncretic with a nominative across a non-syncretic accusative, and they can never share the same stem as the nominative if the accusative has a suppletive stem of its own. If the ergative were to be classified as an inherent case, it would be the only such case to violate these generalizations, as can be illustrated with Dhargari for syncretism (Table 18, repeated here as 26) and with Jingulu for suppletion (Table 15, repeated here as 27).

How then can we set the ergative apart from the (other) inherent cases, and put it in the same box as the accusative? According to an ergative-as-inherent theory, there is only one thing that accusative and ergative have in common: they are both assigned by little v⁰, albeit through different assignment modes. We may then attempt to cash this out by reformulating the case hierarchy as in (25).14

Clearly, however, (25c) still would not be a natural class. Why should all inherent cases pattern alike, irrespective of their assigning head, except when that head is v⁰? And conversely, why should the structural–inherent distinction matter in setting aside the genitive from other obliques but not the accusative from the ergative?

A far neater account is offered by the theory of dependent case developed by Marantz (1991) and Baker (2015).15 According to this theory, case is assigned cyclically, the relevant cyclic domains being TP and DP/NP.16 Importantly, genitive is analyzed as a case assigned within the DP/NP, whereas nominative, absolutive, accusative, and ergative are of course all assigned within the clausal domain. Each domain is globally scanned by the case-assigning algorithm, which goes through three ordered steps.

This theory captures the structural nature of the ergative, and can thus account for the case alternations it takes part in (see in particular Baker & Bobaljik 2017). But most importantly, the theory provides us the right conceptual bases to make sense of the case classes we have found. More specifically, the genitive case, being assigned in a different cyclic domain than the other cases we have looked at, is now actually expected not to be hierarchically ordered relative to them. As for the cases assigned within the clause, the Marantzian algorithm turns out to make reference to the same classes we have observed: UNMARKED – DEPENDENT – INHERENT.17

Insofar as our morphological generalizations are accurate and we wish to make better sense of them, we thus have a novel kind of argument in favor of a dependent-case approach.

Although the main focus of this paper has been on the implications of *ABA for the structure and nature of case categories, the *ABA patterns I have surveyed can also prove helpful in restricting the theoretical space of available morphological models.

In Sections 2–3, I adopted an account of *ABA in suppletion and syncretism which was couched within a simplified version of Distributed Morphology. In such a framework, the terminal nodes of the syntactic tree are bundles of features, each of which is realized post-syntactically by the most specific rule of exponence that matches it. As we have seen, this setup, coupled with the right containment hierarchies, derives *ABA without further ado. However, the models actually used in most research within decompositional-realizational morphology (e.g. DM or Nanosyntax) are generally richer or altogether different than the simple one I have assumed here. I shall therefore move on, before closing, to examine what the main such enrichments and revisions amount to, and on what conditions they can maintain the desired restrictiveness with respect to *ABA.

I will focus first on DM approaches that supplement Underspecification with feature-deleting Impoverishment rules intervening between syntax and exponence (Section 7.1), and I will then move on to Nanosyntactic approaches that replace Underspecification with Overspecification, reversing the directionality of exponent competition (Section 7.2). As I will show, both frameworks can be made to predict *ABA, albeit each with a different tradeoff: on the one hand, Impoverishment must be constrained to apply gradually—in a sense made precise below—so as to not overgenerate ABA syncretisms; on the other hand, Nanosyntax requires a proliferation of case heads in order to extend its treatment to case-sensitive suppletion.

In this paper I have argued, based on a sample of 102 case-inflecting languages, that case-sensitive suppletion and non-accidental case syncretism universally obey the same *ABA restrictions, and that these restrictions make reference to case classes that are most straightforwardly interpreted in terms of theories of dependent case. More specifically, I have argued for the universal containment hierarchy in (41), and discussed how such a hierarchy can derive the observed *ABA patterns across different decompositional-realizational approaches to morphology, with differing analytical tradeoffs.

Framework comparisons aside, I have left several other questions open along the way. At the deepest conceptual level, obvious questions remain concerning the origin of the hierarchy in (41) itself: Where does it come from, and more specifically, how can we explain its tantalizing parallelism with the order in which cases are assigned by Marantz’s (1991) algorithm (structurally biggest cases assigned first, and lightest ones assigned last)?

At a more nitty-gritty level, another underdeveloped aspect of the current proposal concerns the theory of featural similarities between cases assigned within different domains. Judging from the genitive’s exceptional “license to syncretize” (cf. Tables 23, 24, 25 above), it appears as though such cross-domain similarities should be left essentially unconstrained: a case x assigned in domain X could then share features with any case y assigned in domain Y, regardless of x’s and y’s respective case classes. Why this should be so, however, remains to be understood.

Finally, it is worth noting that, throughout the paper, I have been relying on the simple dependent-case system outlined by Marantz (1991), abstracting away from various theoretical additions proposed in subsequent work. These include, for example, the recognition of VP as another potential case-assignment domain alongside nominals and clauses (Baker 2015: § 4.2; cf. fn. 16), the introduction of negative c-command conditions on certain dependent cases (again Baker 2015: § 3.3) and of double c-command conditions on certain others (Harley 1995). Whether all these developments could and should be integrated within the current account is another question I leave for future work.

The additional file for this article can be found as follows: