In the empirical part of this paper, which is laid out in parts 3 and 4, it is argued that Dutch vowel alternating allomorphy is subject to both phonological principles and lexicalisation. As such, it presents a subset of the hypothetical factors that may determine allomorphy, which would also include syntactic contexts. The existing literature mainly focuses on syntactic and phonological factors and the current section presents this state-of-the-art of the theoretical and technical functioning of allomorph distribution.

As pointed out by Bonet and Harbour (2012: 220), there is little agreement in the literature as to which mechanism is responsible for the selection of an allomorph. Indeed, proposals range from stipulations or rankings at Vocabulary Insertion to phonological constraints in OT-based models. Bonet and Harbour point out that the source of the theoretical dispute probably stems from the disparity in the data (see also Bye 2007). Indeed, sometimes the distribution of allomorphs seems to be completely random, whereas other cases of allomorphy seem to follow phonological principles in a fully predictable and optimising fashion. Given this state of affairs, any approach that attempts to capture all data by means of a unified account therefore seems to be doomed to be a less than elegant or satisfying account for at least some of the data.

On top of the fact that there is disagreement on which module should regulate the selection of allomorphs, there is the more basic question on how many modules are involved in allomorph distribution. The mere disparity of the data set might in fact indicate that the corresponding mechanisms and modules are disparate as well. The present paper follows this line of reasoning. In sections three and four I present a Dutch data set that indicates that a specific case of allomorphy shows simultaneously clearly optimising and predictable behavior and random idiosyncrasies. I argue that this state of affairs is actually indicative of the way allomorph selection is organised: it is split over two modules, resulting in two types of empirical patterns. More specifically, I argue that Vocabulary Insertion stipulates the lexicalised, idiosyncratic occurrences of allomorphs. In the absence of lexicalised selection, the competing allomorphs are sent to Phonology as disjunctive exponents of a single vocabulary item. Phonology will subsequently select the phonologically most optimal candidate. This position is supported empirically in later sections. The present section argues for this approach on theoretical grounds by reviewing the pros and cons of existing proposals.

Distributed Morphology is a late insertion model; Syntax merges abstract features and all vocabulary insertion takes places post-syntactically at Vocabulary Insertion, which is an operation at PF. Hence, no exponents are present at Syntax. At the position of the root node (i.e. the lexical node), Syntax contains (at most) an index that refers to the relevant stem at Vocabulary Insertion, other nodes contain bundles of morphosyntactic features (Halle and Marantz 1993; 1994; Harley and Noyer 1999; Harley 2014).

When a syntactic cycle is complete, it is spelled out to PF and LF. At the PF-side, the structure may be subject to certain well-defined morphological operations before it is sent to Vocabulary Insertion. These morphological operations should not concern us here. Vocabulary Insertion is an operation that matches vocabulary items with the syntactic tree. The vocabulary items are acquired items that are stored in a list. At the LF-side, the compositional meaning of the syntactic features is computed. The compositionally derived denotation is combined with information from the Encyclopedia, another acquired list, which contains stored lexical semantics and instructions for (idiomatic) interpretation.

Since Distributed Morphology’s seminal papers (Halle & Marantz 1993; 1994), the insertion of functional (i.e. non-root) vocabulary items is assumed to be subject to competition. It adheres to the Subset Principle, which is in se an Elsewhere Principle, giving priority to more specific rules over more general or default rules. These rules are often based on feature sets: vocabulary items are specified for the features they may realise. The vocabulary item of which the feature specifications are the best matching subset of the features on the syntactic node will be selected to realise the node. However, as allomorphs are mere variants of a single vocabulary item, they are usually specified for exactly the same features. As such, in the context of allomorphy, these rules typically do not depend on features, but on insertion contexts. More complex contexts are then given priority over less complex contexts. For example, the English tense suffixes ∅, -t and -d cannot be distinguished featurally as they all realise the same feature [+past]. What sets them apart is the type of verb with which they co-occur (example taken from Halle and Marantz 1993: 123–124):1

The exponent for which no context is given is the elsewhere form.

The insertion of lexical vocabulary items (also known as stems, roots or lexemes) was assumed to be subject to free choice rather than competition. As a result, competition between allomorphs was assumed to be restricted to the functional domain (Marantz 1997), as only functional vocabulary items compete for insertion in the first place. Instances of stem allomorphy were then postulated to result from readjustment rules, which can be understood as rules that guarantee some phonological readjustments of a stem at Spell-Out.

The theoretical distinction between functional and lexical allomorphy was motivated empirically by the observation that strong suppletion tends to be limited to the functional domain and stems only tend to show weak suppletion (see Marantz 1997 for discussion). However, Harley (2014) puts forward instances of strong suppletion amongst lexical verbs in Hiaki (see also Veselinova 2006). Having falsified the empirical distinction between allomorphy amongst functional and lexical vocabulary items, it becomes pointless to maintain the theoretical and technical distinction. Consequently, she proposes competition at Vocabulary Insertion for roots as well: lexical vocabulary items contain instructions to match an index with a phonological form, as illustrated in (2) (the example is based on Harley 2014). The example illustrates a Hiaki verb (‘to run’) that has two allomorphs, one of which is inserted in a plural context. The vocabulary item, which was merged at Syntax as an abstract index (e.g. the root with index 231) stipulates that the exponent tenne should be matched with this index in a plural context and with vuite in all other contexts:

As the example shows, vocabulary items may contain information on the availability and the distribution of allomorphs. What may determine the use of an allomorph is a stipulation on the vocabulary item that a certain allomorph is the more specific candidate for a certain context. For the example above, the selection mechanism is the stipulation that tenne is a closer match for plural contexts. Note that the two allomorphs spell out the same index and their selection solely depends on an insertion context. Note further that the so-called syntactic selection of allomorphs is strictly speaking not determined by the module Syntax itself: allomorphy is determined at Vocabulary Insertion. It is syntactic in the sense that Vocabulary Insertion takes syntactic contexts into account.

To summarise, in Harley (2014) lexical selection depends on features for functional items and on an index for roots. Once the relevant vocabulary item is selected, the selection amongst its various allomorphs (if any) depends on insertion contexts stipulated at the vocabulary item. Richer insertion contexts precede less specified ones. In other words, allomorph selection still functions as in Halle and Marantz (1993), albeit extended to root allomorphy.

In the previous section we have seen examples of allomorphs that depend on a given syntactic context, without assuming that the allomorph indeed spells out a specific syntactic feature itself. Yet, this possibility also seems to exist. It is, for example, well-known in the literature that syntactic plurality may trigger allomorphs or other irregular exponents. Yiddish, for example, shows allomorphy in plural contexts (Lowenstamm 2007). In the following example the root kind ‘child’ alternates with its allomorph kinder:

An irregular exponent may thus be found in syntactically plural contexts. There is a strong tendency in the literature to analyze these irregular markers as instances of noun class markers of plurality. It is often proposed that the noun class marker is an instance of n°, which merges above the root and which is selected by the plural context. Versions of such a proposal have been endorsed by Lowenstamm (2007) for Yiddish, by Kramer (2009) for Amharic and by Acquaviva (2008) for Breton. In the same vein, Hermans & Postma (2009) have proposed that Dutch vowel length alternation and a Dutch allomorph pattern resembling the Yiddish data in (4) are instances of noun class marking in plural contexts as well, a proposal to which I briefly come back in Section 5.2. In all these proposals, the alleged irregularity of the stem is in fact the spell-out of a syntactic head, viz. a noun class marker. It is thus argued in the literature that a difference in form in such cases reflects difference in structure. Hence, it is referred to as pseudo-allomorphy.

Technically, pseudo-allomorphy can be captured in three ways. Firstly, it can be argued that the instances should be aligned with the cases presented in Harley (2014): the allomorphs are systematically triggered in the presence of a given syntactic head and, as such, they seem to spell out this head, but technically, they do not. They simply systematically appear next to this head, which may be realised by a silent exponent in itself. Secondly, it can be argued that the allomorph is technically not an allomorph, but a concatenation of two lexical items. For example, under such a proposal kinder is not an allomorph of kind, but the spell-out of kind and -er. Under such a proposal, these data do not instantiate allomorphy and they become irrelevant to the discussion. Thirdly, one might argue that a form such as kinder indeed spells out both the root and little n simultaneously. Given that kind and kinder then spell out different feature sets, their selection is subject to the subset principle. Such proposals have to adopt a version of phrasal spell-out and are incompatible with approaches in Distributed Morphology that adhere to the original idea of piece-based realisation. I will come back to this idea in Section 2.8.

A thorough discussion of this issue lies beyond the scope of the present paper. It will become clear that I argue that the data presented in this paper are not to be analysed as syntactic allomorphy.

Lexicalisation may be responsible for allomorphy selection. For example, the participle of the verb uitverkiezen ‘to select’ is uitverkozen, as can be seen in (4):

Yet, there is an idiomatic reading in which a different form is used:

There is nothing systematic to be mentioned about the exceptional use of uitverkoren in the example above. A connection has been stored between an irregularity in form and an irregularity in meaning in a specific collocation. The use of an irregular form has simply been listed as the conventionalised form to express a specific idiomatic meaning. The selection of the allomorph is then an arbitrary convention, a conventionalised irregularity. An allomorph may thus be selected in a specific context despite the fact that there are no principled, i.e. phonological or syntactic, grounds to do so (see also Section 2.5).

The mechanics presented in Harley (2014) on syntactic allomorphy can be straightforwardly extended to incorporate such examples of lexical allomorphy. Just as syntactic insertion contexts can be stipulated on a vocabulary item, so can lexicalised insertion contexts. In fact, there is a good reason to group them technically. The information both types of insertion contexts rely on can be read off from the syntactic tree. This is obvious for allomorphy based on syntactic insertion contexts. But also for lexical contexts the tree does contain all the necessary material to recognise a relevant collocation, as its nodes contain the indices or features of the other lexical items referred to. Furthermore, both for lexical and syntactic insertion contexts, no systematic rule is at work (beyond locality). The distribution of the allomorph simply depends on a listing associating the use of a specific allomorph with neighbouring material in the tree.

As described above, Harley (2014) argues that the syntactic selection of an allomorph can be understood technically as a stipulation on the vocabulary item, determining in which syntactic context a certain allomorph should be inserted. Mutatis mutandis, if the selection of an allomorph is phonological, one could stipulate a phonological context on the vocabulary item, as in the following abstract example:

Again, in such a scenario it is not the module Phonology in itself that may select the allomorph, it is rather a phonological context stipulated on the vocabulary item that will ensure the insertion of the phonologically more optimal candidate.

An approach such as the one sketched here is presented in Paster (2006). Discussing suppletive forms of affixes, she proposes that all conditions determining allomorphy are simply part of the subcategorisation frame of the vocabulary item, in casu the affix. As a result, vocabulary items in her model may have an elaborate subcategorisation frame, including both syntactico-semantic and phonological insertion criteria (see, for example, Paster 2006: 12).

From a descriptive point of view, such subcategorisation frames successfully capture all the facts. It suffices to adequately list all insertion contexts with an appropriate ranking. Model-wise, the proposal dovetails in general with Distributed Morphology, as it extends ideas already present in the seminal papers (cf. example 1 in Section 2.2). However, even though, technically, the stipulations on the vocabulary items will derive the desired results, we may be reluctant to adopt these adjustments as the final say on the organisation of vocabulary insertion for two reasons. Firstly, stipulating the relevant phonological context on the vocabulary item does capture the observation that a specific form will be inserted in a specific phonological context, but it does not express the insight that such phenomena are often motivated. In fact, one could stipulate just anything (that respects locality conditions) as an appropriate phonological context for insertion for a given allomorph. In this sense, it is a brute force solution. The insight that the insertion of an allomorph often actually happens to optimise the phonological make-up of the word is lost and not expressed by the current mechanism.

Admittedly, according to Paster (2006) this result is actually an advantage of the approach. She points out that not all phonologically-driven cases of allomorphy are actually optimising. She presents twelve examples from various languages in which the distribution of suppletive forms of affixes is clearly determined by phonological properties of the lexical item involved (Paster 2006: 76–98). Yet, the use of these suppletive forms is at best neutral; their occurrence does not optimise the word phonologically.

Given the existence of these facts, note the following. As rightfully pointed out by Paster, any account dealing with the distribution of allomorphs has to be able to capture phenomena that are irregular, arbitrary or lexicalised in nature. A theory in which the most optimal candidate invariably wins is simply empirically inadequate. Note that it follows in particular, as Paster (2006) points out, that trying to capture phonologically motivated types of allomorphy by solely relying on Optimality Theory will therefore be an ordeal, given that it is easy to find non-optimal instances of phonological allomorphy, a point to which I come back below.

Nevertheless, Paster’s approach asks us to throw the baby out with the bathwater. There is no contradiction in fully recognising the existence of counterexamples, which certainly should be captured one way or another, and adhering to the insight that a general phonological principle may determine other instances of allomorphic distribution. There are cases in which phonologically conditioned allomorphy does show regular optimising behavior and Paster’s (2006) subcategorisation-frame based approach does away with the tools to capture them, given that all phonologically motivated suppletion is technically reduced to idiosyncratic properties of vocabulary items.

The second reason because of which we may be reluctant to adopt Paster’s (2006) approach fully is the fact that phonologically-driven allomorphy may show uniform behaviour over various vocabulary items. From a phonological point of view, this phenomenon is not hard to understand; all vocabulary items that share a relevant phonological feature may be subject to the same phonological condition. Yet, under a subcategorisation-frame based proposal, such a natural grouping becomes a coincidence. The fact that the linguist understands why certain vocabulary items may show similar behaviour cannot be expressed in a model that merely relies on stipulations on individual lexical items.

In sum, subcategorisation-frame based proposals have strong descriptive force; all conditions determining allomorphy can be stipulated on the lexical item. Furthermore, it does recognise and capture the existence of non-optimising counterexamples. The disadvantage is that these stipulations are indeed mere stipulations, which fail to express insights. Another disadvantage is that the approach is lexical item based, which fails to express patterns generalising over various lexical items. It appears that the approach has not much to offer when it comes to phonologically driven patterns, but it does offer us the tools to deal with exceptions.

Just as Paster (2006), Nevins (2010) stipulates phonological conditions for allomorphy selection at Vocabulary Insertion. Yet, he takes a slightly different approach. He simply specifies the phonological rule as a contextual condition for insertion on the vocabulary item, as in the following example (taken from Nevins 2010: 22, his example (38)):

The advantage of incorporating a rule rather than a phonological context is clear; the vocabulary item expresses an insight rather than an arbitrary mechanism. It may seem like we have addressed the concern.

However, consider the following problem. If one allows both syntactic and phonological conditions to be specified on the vocabulary item, we define Vocabulary Insertion as a hybrid operation. It should be able to read both syntactic and phonological conditions simultaneously. In this respect the stipulation that an allomorph may be sensitive to a specific phonological context, as in Paster (2006), is the more conservative stipulation; Vocabulary Insertion simply must be able to check surrounding syntactic and phonological features. However, if we adopt Nevins’ proposal, Vocabulary Insertion must be able to actually interpret a phonological rule. It defines Vocabulary Insertion as an operation that is able to execute quite some phonology. Yet, simultaneously, we want it to be able to check for adequate syntactic conditions as well, following Harley’s proposal. In sum, it defines Vocabulary Insertion as a two-headed dragon.

Note, furthermore, that a single lexical item may be subject to both insertion contexts and phonological stipulations. Such stipulations are ranked according to the Elsewhere Principle and one of them will precede the other one. Now, given that stipulations are still related to lexical items, the approach is ill-fitted to capture more general patterns over various lexical items. More in particular, we will see that insertion contexts systematically win over all phonological constrains (see Sections 2.8 and 2.9). This systematic ordering over various lexical items are technically nothing but instances of coincidence.

Finally, one might consider the fact that phonological constraints are ideally understood as universal constraints. Vocabulary Insertion, in contrast, is a list of acquired information. As such, it is odd to assume that Vocabulary Insertion hosts phonological principles.

In sum, it is advantageous to incorporate a phonological rule rather than a phonological context as an insertion context. However, it implies that Vocabulary Insertion can execute phonology and that it hosts both innate and acquired insertion principles. The relation between Vocabulary Insertion and Phonology proper becomes unclear: if Vocabulary Insertion can handle Phonology, is it then defined as the module Phonology or does it still co-exist with a separate module called Phonology?

Optimality Theory (McCarthy and Prince 1993) defines morphological and phonological conditions for allomorphy selection as constraints. As such, morphological conditions and phonological conditions are evaluated in the same module. OT thus relies on a hybrid module as well. Older work in OT assumes that these conditions are ordered: one can formulate a general constraint that stipulates that all phonological conditions are to precede all morphological requirement (McCarthy and Prince 1993) or the other way around (Yu 2003: 108).

There is of course the well-known general problem that it is hard to see how these original proposals can be adopted by a realisational model such as DM (and see Paster 2006 for a thorough critical discussion). Distributed Morphology cyclically matches vocabulary items to syntactic nodes from the root outwards and the match is evaluated for each node within each cyclic step by the Elsewhere Principle. As such, it is principally incompatible with a model that maps a surface representation to an underlying representation for a phonological word without taking into account its internal structure (as discussed at length in Embick 2010).

Apart from this theoretical objection, there are two empirical objections. Firstly, as pointed out by Paster (2006: 77) in the domain of phonological allomorphy non-optimising examples can be found easily. They are challenging to OT, to say the least. Secondly, OT evaluates input candidates to derive surface forms. There are no grounds for underlying representations to trigger phonological allomorphy. Yet, underlying representations may trigger allomorphy, as will become clear in Section 3.3.

Wolf (2008) presents a serial version of OT to deal with phonological allomorphy (Candidate Chains, McCarthy 2007). In such an approach, candidates may improve incrementally. As such, the theory opens up the possibility to integrate underlying requirements into intermediate steps. Wolf’s main proposal is that morphological insertion criteria and phonological insertion criteria are evaluated in the same module, i.e. Phonology. Wolf rewrites the subset principle as a series of constraints that guarantee that the candidate of which the features are the closest subset of the syntactic node will outrank less optimal matches. However, unlike the older versions of OT, he does not assume that there is an intrinsic ordering between constrains guaranteeing feature matching and those guaranteeing the application of phonological principles: morphological and phonological constraints can interleave. Just as Nevins (2010), he thus assumes that a single module hosts both universal phonological principles and acquired information, i.e. the link between exponents and the feature sets they realise.

Now, it is important to note that the discussion in his thesis is limited to two particular types of allomorphy. Firstly, he addresses instances of true phonological allomorphy, i.e. data which can be fully captured on phonological grounds as they show regular, optimising behavior. Secondly, he presents instances of phonologically motivated lexical item selected which, arguably, would not even be called allomorphy in Distributed Morphology. For example, he discusses the distribution between the determines el and la in Spanish. As is well-known, la is selected in feminine NPs, el is selected in masculine ones. However, el may also be selected by feminine nouns that begin with stressed [á]. Clearly, the distribution between el and la is thus partially phonologically motivated. However, strictly speaking, el and la may not be allomorphs of a single lexical item, but simply two lexical items competing for insertion. This example characterises his approach: allomorphs are distinguished featurally and the selection is then done by a morphological constraint that will select the closest matching feature set.

Wolf is forced to invariably assume featural distinctions between allomorphs. A first problem is pointed out by Bonet & Harbour (2012: 227): the featural distinction may be entirely stipulative. The second problem is that the approach is at odds with the essence of how allomorphy is understood in Distributed Morphology. Recall from Section 2.2 that allomorphy in DM is not understood as competition based on feature sets; it is based on ranked insertion contexts. Wolf does integrate Vocabulary Insertion in Phonology by rewriting the subset principle as constraints, but he remains silent on those data that are a central aspect to the understanding of allomorphic distribution in DM, i.e. the ranking of insertion contexts. In sum, it is unclear how Wolf’s proposal can be applied to instances of allomorphy that are not to be distinguished featurally, as discussed in Section 2.2 and 2.4.

The empirical domain discussed in this article does not match Wolf’s approach very well. We will see that allomorph selection for Dutch vowel alternating stems is both based on phonological principles and on stored, lexicalised information. Because some of the data are lexicalised, rather than being based on a selection mechanism relying on syntactic features, the data are at odds with Wolf’s proposals. I will therefore not come back to this approach in later sections.

Booij (1998) discusses instances in Dutch morphology where phonological principles clearly seem to regulate the distribution of strong and weak allomorphs, but the application of these phonological principles are not without exception. For example, he discusses the by now well-known fact that the two competing Dutch plural affixes -s and -en are subject to syllabic well-formedness: -en is favoured if it transforms the root into a trochee (with right directionality). Hence, the Dutch plural of kat ‘cat’ is katten, but the plural of dokter ‘doctor’ is dokters. Even though this tendency is undeniably present in Dutch, counterexamples and examples of regional variation are not hard to find. For example, as Booij points out, speakers in the Netherlands favour the phonologically less optimal plural form tests ‘tests’ for the noun test, whereas Belgian speakers will use the phonologically expected form testen. Speakers in the Netherlands simply conventionalised the unexpected form.

To account for such examples, Booij (1998) proposes that stems and affixes are marked with subcategorisation features which may be of any kind (phonological, syntactic, …). These features regulate morpheme concatenation in morphology. Morpheme concatenation acts as a generator that generates possible candidates which are then sent to Phonology for evaluation in an OT fashion. As subcategorisation features precede phonological principles in the proposal, Booij can guarantee that phonology will operate within the language’s morphological boundaries and he can make sure that phonology -and nothing but phonology- indeed takes place at a designated module, viz. Phonology.

Mutatis mutandis, the proposal can be adopted in Distributed Morphology. Subcategorisation features can be understood as being part of Vocabulary Insertion, as in Paster (2006) and Harley (2014). The output of Vocabulary Insertion, which can include various candidates for the spell-out of a single node, are then shipped to Phonology for further evaluation. It will become clear in the next section that the present proposal adopts exactly this idea.

Bye and Svenonius (2010; 2012) formulated a proposal that shows similar features, but which differs in important aspect. They propose to split Vocabulary Insertion into two different operations, which they call Match and Insert. Match precedes Insert; Match’s output is Insert’s input.

Match can see syntactic features and syntactic structure, such as dominance, movement and phase boundaries and it matches lexical items to the syntactic tree. As in Distributed Morphology, it is assumed that those lexical items are chosen that realise a maximum of features present in the tree. Domains for insertion are not terminal nodes, as in Distributed Morphology, but rather Spell-out domains, i.e. phases. As such, a lexical item may realise a span of terminal nodes (cf. Williams 2003).2 Such a span is understood as a segment of an extended projection. For example, the noun plus number marking is understood as a phase and thus may be realised as a span in the noun’s extended projection, i.e. the DP. In the English noun phrase, the noun will incorporate into the plural head, due to the fact that English number marking is suffixal. This type of linearisation is characteristic of the proposal: all linearisation that can be done in syntax will be done in syntax. The suffixal nature of the English plural thus does not need to be stipulated as a property of the suffix, as it is already derived at syntax. This cyclic domain is sent to Match, where a portmanteau morpheme, such as geese and mice, or several lexical items, such as ballerina-s, may realise this span. A form such as mice will be given preference over a form such as *mouses or mice-∅ due to a principle called Minimize Exponence: using less exponents to match the syntactic features are better than using more exponents. Note that the model thus has a mechanism to capture allomorphs that disjunctively realise different syntactic feature sets: mouse and mice are allomorphs and their distribution is regulated by postulating that they realise different features. The model allows for a different type of allomorph selection as well: the model allows various disjunctive forms to be selected by Match. The choice between these exponents is postponed. As such, allomorph selection can be assigned to a later module.

Match’s output are candidates for insertion and are sent to the module Insert. Insert has the following tasks: it selects allomorphs on phonological grounds in case of disjunctive exponence, it linearizes the structure and it builds an underlying phonological representation. Of particular interest to us, is that the module thus contains an allomorph selection mechanism. Bye and Svenonius (2010: 14) provide the following example. The lexical item of the English indefinite article contains the following disjunction:

Given that the choice between an and a is based on phonological criteria, the selection is not established by Match, which can only take into account syntactic criteria. The disjunctive candidates are thus both sent to Insert, which picks the best candidate on phonological grounds.

An important advantage of the split approach presented here is that the insertion mechanism is able to take both syntactic and phonological requirements into account, while it does not require a single operation to interface with both syntactic and phonological insertion contexts. However, note that the phonological selection in (9) is based on an insertion context rather than on a principle. This is a missed opportunity. In Section 2.6 we argued that if a phonological selection can be formulated as a principle, one misses a generalisation by reducing it to a context. We thus end up with a separate module for phonology that does not really execute phonology with full force.

Bye (2007) explicitly discusses allomorphy in yet another split approach. He concurs with Paster (2005) that many examples of allomorphy are not phonologically optimal. He points out that these examples, which he labels morpholexical are language-specific and inviolable. If these rules are not respected, they lead to ungrammaticality. In contrast, phonologically selected examples of allomorphy are selected on the basis of universal, violable principles that guarantee the selection of an optimal candidate. According to Bye the process of Eval precedes a Morpholexical Control mechanism: the output of Phonology is checked by Control and results that are not compatible with language-specific morpholexical criteria are rejected. Bye’s (2007) split approach model thus succeeds in capturing both phonological and morpholexical selection. The mechanics of his proposal fit the data: phonological selection is done in a bona fide phonological module that operates on the basis of universal phonological principles. Morpholexical selection, on the other hand, works on the basis of language-specific, listed and and inflexible information. Bye (2007) thus presents a model that successfully and strongly captures the disparate data. He argues to acknowledge that both types of data exist and he gives them an appropriate place in the model. The present article aims to contribute to the same goal. Bye himself points out that a possible objection against the model might be that OT is complemented with a set of declarative constraints (in the control mechanism). In the following section I propose not to adopt the control mechanism. I argue that it suffices to let Vocabulary Insertion precede Phonology (as we assume in Distributed Morphology anyway) to accommodate for both data and both selection mechanisms.

Let us take stock of the data and the ideas presented in the previous sections. Empirically, we have encountered four different types of allomorphy: some allomorphs are sensitive to a syntactic context (Section 2.2), some are sensitive to a lexical context, which is possibly phonologically non-optimal (Section 2.4), some allomorphs disjunctively realise different syntactic feature sets (Section 2.3 and the discussion on Wolf 2008 in Section 2.7) and some differ qua phonological optimality (Section 2.7). Approaches that attempt to unify allomorphy into a single module will either ignore some of the data and be observationally inadequate (cf. the critique in Paster 2006 and Bye 2007 on Wolf 2008) or they will have to rely on rich subcategorisation frames (as in Paster 2006), which is a brute force solution to achieve observational and descriptive adequacy.

Now note that three of the four types of allomorphy can be captured by Vocabulary Insertion. We have seen that Vocabulary Insertion sees information present in the tree and it can deal with disjunctive feature sets and disjunctive insertion contexts via the Elsewhere Principle. As such, it can successfully deal with allomorphs realising different syntactic feature sets and it can take into account allomorphy sensitive to a syntactic context. Given that Vocabulary Insertion is in itself a list of lexical items, it also can see lexicalised information stipulating stored irregularities on those lexical items. Such lexical items will have the following, familiar format:

Let us thus assume that Vocabulary Insertion occupies its familiar spot in the Y-model and that it regulates the selection of these three types of allomorphy, relying on no other basic mechanisms than those that were already proposed in Distributed Morphology’s seminal papers.

I now adopt the idea proposed by Bye and Svenonius (2010) that the output of a Vocabulary Insertion mechanism may be a set of candidates. To do so, we do not have to alter our assumptions on Vocabulary Insertion drastically. We simply have to allow a tie between candidates that seem to be equal options at Vocabulary Insertion and which can only be distinguished on the basis of phonological criteria. It is a minor modification of Vocabulary Insertion as we know it. I propose that a lexical item may be marked for a set of unranked exponents, i.e. allomorphs, at Vocabulary:

Such a situation will only occur if there are no lexical or syntactic criteria to distinguish between the allomorphs. This candidate set is then shipped to Phonology, which will select the best candidate on the basis of universal phonological constraints. The possibility of lexical items, such as the one proposed in (11), which may exist alongside familiar lexical items, such as the one in (10), is basically the only innovation here, but its effect is considerable. Note that the fact that the allomorphs are not ranked is not a problem. Stipulating an elsewhere form is not necessary, given that one of the forms will always be more optimal than the other one phonologically.

It is important to note that nothing prevents us from mixing the ingredients presented in (10) and (11). As such, a morpholexical stipulation at the vocabulary item can block a richer set of candidates right from the start, as illustrated in the abstract example in (11):

(12) says that one allomorph will always be inserted in context α, in all other contexts the decision is up to Phonology. We have seen that any approach to allomorphy selection should be as successful in capturing the phonological patterns as in capturing the pervasive irregularities. As such, having a mechanism that can give priority to exceptions is an important addendum.

In sum, the purpose of this article is to defend a split approach to allomorph distribution which sets apart allomorphy based on stored insertion contexts from allomorphy based on phonological principles, and as such it argues against proposals that group all criteria together in Vocabulary Insertion (e.g. Paster 2006) or Phonology (e.g. Wolf 2008). It argues that both types should be assigned to their own designated module: insertion contexts are part of Vocabulary Insertion, phonological criteria belong to Phonology. As such, the approach takes advantage of the strength of both modules: Vocabulary Insertion, by definition a stored list, captures irregularities and stored insertion contexts, Phonology, based on universal constraints, provides for phonologically optimising patterns. Furthermore, these modules are ordered: Vocabulary Insertion precedes Phonology. The main reason to assume this order is the logic of the Y-model. Vocabulary Insertion interfaces with the morphosyntactic features and indices present in the syntactic tree. Hence, its input must be the syntactic tree. Phonology, on the other hand, derives a surface representation from an underlying representation, hence it must be fed the underlying representation of the exponents, which follows immediately if it follows Vocabulary Insertion.

A proposal on the exact nature of Phonology lies outside the scope of this article beyond the assumption that it is some kind of optimising model (see Bye 2007 for a discussion). It will become clear that the data in the present article suggest that also underlying representations can be subject to phonological principles determining allomorph distribution. This criterion is a desideratum for a phonological module in my opinion.

In the following sections I discuss a data set from Dutch that shows how the proposed model is beneficial. The field has gone back and forth on concentrating on either irregular, phonological non-optimal allomorphy or fully phonologically optimising allomorphy, rather than acknowledging that both instances co-exist (as emphasised in Bye 2007). Dutch contains a data set which illustrates exactly this point: within a single data set, both patterns clearly co-exist.

Van der Hulst (1985) contains a proposal on why vowel length alternation might optimise Dutch syllable structures. Consider the following examples of vowel length alternation in Dutch from the domain of derivation (Van der Hulst 1985: 63). They show an alternation between stems with a short vowel in morphologically simplex contexts and forms with a long vowel in derived forms.

Van der Hulst (1985) provides a phonological account: he proposes that the stem with the long vowel is selected to avoid ambisyllabicity. The proposal goes as follows. A Dutch minimal rhyme is at least bimoraic. The hypothetical forms in (13) are therefore excluded by Dutch phonology:

As a result, short vowels create a context of ambisyllabicity in Dutch. To avoid a rhyme which is monomoraic, Van der Hulst (ibidem) proposes that a consonant in the onset of a following syllable may function simultaneously as the coda of the previous syllable. In other words, the consonant may be ambisyllabic. This is illustrated in the example in (15) in which the /k/ is shared due to the fact that the short vowel /ɑ/ only occupies a single moraic position.

Ambisyllabicity, of course, does not occur in closed syllables or if the rhyme of the first syllable contains a long vowel. Both closed syllables and long vowels occupy two moraic positions. As such, they fulfil the requirements of the minimal Dutch rhyme on their own.

Van der Hulst (1985) does not only argue for ambisyllabicity, he also proposes that spreading of the vowel is preferred in Dutch over spreading of the consonant. In other words, vowel length alternation is preferred over ambisyllabicity. Hence, if a stem allomorph with a long vowel is available for the root, this allomorph will be selected to fulfil the phonological requirement of the minimal rhyme. Whether such an allomorph is available is a stored property of the root. This leads us to the following phonological rule:

Van der Hulst’s proposal shows similarities with Lahiri & Dresher’s (1999: 706–710) account of the productive process of Open Syllable Lengthening in Middle Dutch.4 They propose that there was a pressure to maximize the main stressed foot. In other words, monomoraic stressed open syllables, i.e. open syllables with a short vowel, have shifted to bimoraic open syllables, i.e. open syllables with a long vowel. The authors point out that stressed light syllables have to be bound together with a second syllable in order to acquire the needed second mora as the head of a foot must dominate at least two morae. It is not pointed out explicitly by the authors, but an immediate side-effect of the pressure to maximize the main stressed foot is that they no longer require being bound to the second syllable. As such, the account is similar to Van der Hulst’s proposal.

Lahiri & Dresher (1999) and Van der Hulst (1985) thus have a similar process in mind, the main difference being that Lahiri & Dresher (1999) formulate the principle as motivated by the foot, preferring a bimoraic head, whereas Van der Hulst (1985) formulates it as a requirement of the syllable, preferring vowel lengthening over ambisyllabicity. Lahiri & Dresher’s (1999) proposal was formulated for Middle Dutch, but it is interesting to check whether it fares better for contemporary Dutch than Van der Hulst’s (1985) proposal. Both proposals make a different empirical prediction when it comes to vowels in open syllables, followed by a second syllable, in non-stressed positions in those stems that show the relevant vowel alternating allomorphy. In short, we should look at words in which the relevant vowel occurs in an environment that is subject to the syllabic configuration relevant to Van der Hulst’s proposal, without being the head of the foot, which is the main criterion in Lahiri & Dresher’s (1999) proposal. Such contexts can be created by adding stress-bearing suffixes to those nouns in which the relevant vowel is not in a stressed position, as in (17). The suffixes serve to provide a second syllable in the configuration. In the examples, main stress is indicated by a superscripted accent, secondary stress is indicated by a subscripted accent, the vowel that changes under allomorphy is given in bold. The secondary stress corresponds to the main stress of the stem when it would not bear a suffix. The transcriptions are based on Heemskerk & Zonneveld (2000).

Despite the absence of stress, the stem allomorph with the long vowel does appear in the examples in (17), even though the vowel is not the head of the foot. It thus appears that the relevant syllabic context suffices to trigger the allomorph with the long vowel. Given the data in (16), it seems that Van der Hulst’s proposal has better empirical coverage for contemporary Dutch than Lahiri & Dresher’s (1999) proposal (which has been formulated for Middle Dutch). As such, we will proceed with Van der Hulst’s proposal as formulated in (15).

It is clear that Lahiri & Dresher’s (1999) account of the Middle Dutch facts and Van der Hulst’s (1985) account of Dutch are similar in nature. It is interesting to note that, as such, it is reasonable to assume that the underlying prosodic pressure that motivates the stem alternation in contemporary Dutch is probably the same as the one that motivated the original productive phonological process in Middle Dutch. Dutch may have lost a phonological process, but it did not lose its settings on what constitutes an optimal prosodic configuration and we still see it kicking in as soon as it has a stem allomorph to satisfy its demands.

Standard Dutch has two plural markers, viz. –en and –s. In general, they do not give rise to any changes in the stem. This is illustrated in (17)–(20):

However, there are around thirty to forty irregular nouns which do show a stem alternation (see also Booij 1995: 72). The root’s vowel lengthens in the plural and it may lengthen in the diminutive. An example is given in (21):

I mention the diminutive forms here for good measure, but I postpone a discussion of these forms till Section 4.1.

For the relevant stem alternating nouns, the vowel length alternating pattern for number inflection in the non-diminutive forms is fully regular: in non-diminutive forms singular nouns select the allomorph with the short vowel, plural nouns select the allomorph with the long vowel. The data thus allow for the following empirical generalisation:

The data in this respect thus do not show some irregular behaviour that is specific to some vocabulary items. They allow for a generalisation. The fact that it is possible to generalise over data suggests that a rule is at work, rather than some stipulations at Vocabulary Insertion. Indeed, in what follows I discuss the fact that it is possible to account for the generalisation in (22) on the basis of the phonological rules in (15).

Van der Hulst (1985) pointed out that his approach to vowel length alternation presented in (15) captures the occurrence of the long vowel in non-diminutive plurals. When the plural marker –en attaches to a root the plural marker will occupy a separate syllable. Due to the Syllable Contact Law (Venneman 1988) which results in maximal onsets, the onset of this syllable contains the root’s final consonant, as in (23).

Example (23) shows the plural of the noun zoon ‘son’. Its stem has only one allomorph, which contains a long vowel. The example in (23)a represents the morphological structure,7 (23)b shows the syllable structure.

If the root’s rhyme consists of a short vowel followed by a single consonant the syllable structure of the plural form creates a context of ambisyllabicity. Hence, an allomorph with a long vowel is selected when available to avoid it, as proposed in (16).8 The structure in (24)a is the morphological structure of baden ‘baths’, the one in (24)b is the phonological one.

The phonological approach immediately captures why the allomorph with the long vowel occurs if the root is string adjacent to the plural marker -en. In other words, it accounts for the omni-presence of the allomorph with the long vowel in the non-diminutive plural form. The stem allomorph with the short vowel, on the other hand, is selected when there are no phonological grounds to prefer a long vowel, as is the case in a singular NP, and it thus appears to be the elsewhere form.9 Consider, in this respect, a vowel length alternating noun that may select both the plural marker -en and -s. As expected, the vowel will only lengthen in the phonologically relevant context, i.e. in front of -en (Booij 1998):10

In the context of non-diminutive number inflection, the distribution of the stem allomorphs is thus fully and without any exception regulated by means of the phonological rules in (16).

Zonneveld (1976, 1981–1982) points out that when stems for which an allomorph with a long vowel is available occur as weak verbs, the long vowel can be attested throughout the inflectional paradigm, even though the singular forms are not open syllables:

Needless to say, the occurrence of the long vowel in the singular forms is unexpected based on their surface phonological forms; at least for the singular forms there does not seem to be a second syllable present that could trigger a problematic context of ambisyllabicity. At first sight, one might therefore guess that these patterns are irregular. However, there is no denying that the data behave in a strictly uniform pattern, which, indeed, allows for an empirical generalisation:

The issue has been addressed by Zonneveld (1976; 1981–1982). He captures these data by arguing that the underlying representations of these verbal forms do contain a second syllable, i.e. a schwa which functions as the verb’s theme vowel. Interestingly enough, he argues that the postulation of such a theme vowel does not only capture the presence of the long vowel, but also other, seemingly unrelated, unexpected phonological phenomena in the domain of Dutch verbs, such as d-weakening and schwa-deletion. For all these phenomena it is known independently that they occur in the presence of a vowel in Dutch. Taken together, these phenomena will allow the language acquiring child to assume the presence of such a theme vowel in the context of verbs (and only in the context of verbs!), even though it never surfaces. If one accepts Zonneveld’s conclusions, the exception-less presence of the long vowel in the verbal forms in (26) follows immediately. For the plural forms the overt number inflection provides the required phonological environment, for the singular forms the underlying schwa provides the phonological context that triggers vowel length alternation, as summarized in (28).

Note that for the singular forms the phonological allomorph selection takes into account the underlying representation.

Zonneveld (1976; 1981–1982) noted that the past tense of some strong verbs in Dutch may show lengthening in the plural forms, i.e. those forms which receive an onset-less following syllable through number agreement. They show a short vowel in the singular.11 Yet, a long vowel appears in the plural as the stem is followed by the plural inflectional marker -ən. Again, the data adhere to the same phonological principle:

This pattern is exception-less: all stems for which an allomorph with a long vowel is available are subject to the generalisation, which is illustrated in (30)–(32).12

In short, the past tense of strong verbs shows the pattern which is expected on phonological grounds due to overt agreement affixes.

In the present section I have presented Van der Hulst’s insight. Using a long vowel, when available, optimises syllable structure. It avoids ambisyllabicity in the presence of a following onset-less syllable. Three empirical domains are subject to this phonological condition, viz. plural non-diminutive nouns, Dutch morphologically simplex weak verbs and past tenses of strong verbs. For plural nouns, weak plural verbs and strong past plural verbs the following syllable is an overt inflectional morpheme, -ə(n). For singular weak verbs the following syllable is an abstract, underlying schwa.

Note that the principle is not only clearly optimising, but the same phonological principle has a predictable result across lexical items and across syntactic contexts. It should be clear that an approach that merely stipulates the occurrence of the stem allomorph as an insertion context at the level of the individual lexical items fails to capture the true nature of the phenomenon. The data rather suggest that the allomorph selection in this section is regulated by a phonological principle.

So far we have seen that many occurrences of the stem allomorph with the long vowel can be ascribed to phonology: if a following syllable causes the stem to be an open syllable, an allomorph with a long vowel will be selected, if available, to avoid ambisyllabicity. We have seen two domains in which this pattern is exception-less, viz. nominal plural marking and verbs. In contrast, we have also encountered a domain in which this phonological rule seemed to lead to a strong tendency rather than an empirical generalisation: the distribution of stem allomorphy for diminutive forms largely adhered to phonological generalisations, but not in an exception-less manner. Lexicalised exceptions seemed to play a role in this domain. In the present section I discuss data from the domain of morphological derivation. They behave on a par with the diminutives: most often one attests the allomorphic distribution which is expected from a phonological point of view, yet not without exception.

In Section 3.1 I already cited the following paradigm noted by Van der Hulst (1985: 63), which shows stems merging with a derivational affix:

I discussed that the long vowel appears in context that would otherwise cause ambisyllabicity. Similarly, in (62)a–b, vowel length alternating stems merge with the derivational affix -elijk, causing the stem to become an open syllable. Again, the stem with the long vowel is expected on phonological grounds. The examples contrast with the example in (62)c, a noun for which no stem allomorph is available:28

In short, we see again that, quite generally, if a stem occurs in a phonological environment that causes it to appear as an open syllable and if a stem allomorph with a long vowel is available, that stem allomorph will be selected in Dutch to avoid ambisyllabicity.

Yet, a few counterexamples are attested. Booij (1999: 88) mentions the following examples:

Another example worth mentioning in this respect is the following:

In all examples, the stem contains a single final consonant and it is followed by a vowel, making the stem an open syllable. Yet, an allomorph with a long vowel does not appear. In sum, derivational morphology shows instances in which allomorph selection is but a stored irregularity. As was the case for diminutives, these instances are clearly the exceptions and do not form the regular pattern. However, there is no denying they exist.

So far, I have discussed examples in which the allomorph with the short vowel appears while the one with the long vowel is expected phonologically. The reverse situation occurs as well. Allomorphs with long vowels may be attested in adjectives and adverbs that do not show the expected phonological structure at all; the stem is not an open syllable. Examples are shown in (65).

The allomorph invariably stands in an environment in which the allomorph is selected on phonological grounds in earlier stages of Dutch. It is a reasonable assumption that, subsequently, they have been lexicalised as such. This applies to the forms in (65). They are both derived from forms which were inflected for case and as such contained an extra syllable (see Woordenboek der Nederlandsche Taal):

The occurrence of the allomorph in these environments further supports the claim that the distribution of the vowel alternating allomorphs may rely on lexicalisation.

We have seen that vowel length alternation in Dutch shows two patterns, viz. SLSS and SLLL, as summarised in Table 1, which is repeated in this section (S: stem with a short vowel, L: stem with a long vowel).

It is striking that only these patterns exist. They certainly do not exhaust all hypothetical possibilities as listed in Table 2. The present section addresses this issue.

Let me start with a remark. One could argue that, in principle, any pattern could be stored as a lexicalised pattern and according to this logic no patterns should be excluded. Even though this is a fair point in principle, it is not a reasonable expectation. Lexicalised exceptions historically go back to forms that once were motivated. More specifically, they go back to forms that did contain the relevant phonological context to trigger the allomorph in the past, as we have seen in Section 4.3 (and see Lahiri & Dresher 1999 on Open Syllable Lengthening in West-Germanic). As a result, we do find lexicalised exceptions in narrowly defined domains, such as the diminutive or morphological derivations and they are systematically absent from other domains.

First consider the following hypothetical patterns: SSSL, SSLL and SSLS.29 These patterns express that a hypothetical noun, for which a stem allomorph with a long vowel exists -as shown by a diminutive form- fails to select this allomorph for the non-diminutive plural. In other words, it fails to grasp the opportunity to optimise the non-diminutive plural phonologically. Such nouns are not attested.30 Note that this observation strongly supports the claim that phonological optimisation is the main factor in the distribution of vowel alternating stem allomorphs in Dutch.

The SLLS pattern is phonologically inconsistent as both for the singular and the plural diminutive form the root is followed by the exact same diminutive affix. Hence, given that they share the same phonological context, it is predicted they should contain the same allomorph.

The illicit patterns LSSS, LSLS, LSSL, LSLL express that a vowel shortens in the regular plural. Such a process would be far from optimal by the principles of Dutch syllabification as it creates the dis-preferred ambisyllabicity in the non-diminutive plural form.31 There is yet another aspect that we have not addressed so far that renders these forms far from optimal. Kager and Zonneveld (1985–1986) argue that the Dutch rhyme is bimoraic and that the final consonant of a trimoraic syllable occupies a position in the syllable’s appendix. Empirical support for this claim comes from the fact that trimoraic syllables are restricted to word-final positions. Given that appendices by definition only occur word-finally, the observation is immediately captured by proposing that the Dutch rhyme is in fact bimoraic. It is therefore reasonable to assume that superheavy syllables are less optimal than heavy syllables. It now immediately follows why a long vowel will not appear in the non-diminutive singular. A short vowel results in a bimoraic rhyme, a long vowel would result in a more marked syllable, which has to assign one consonant to the appendix. We thus consequently expect the short vowel in the non-diminutive singular and this is exactly what we see. This observation is not trivial. Again, it indicates that phonological principles are an important factor in the distribution of allomorphs in this domain.

The fact that we have phonological reasons to assume the short vowel in the non-diminutive singular form implies that this form is not per se a default form at Vocabulary Insertion. It seems to be empirically incorrect to state that it occurs in elsewhere positions. It rather seems to occur in those positions where its moraic format is actually preferable.

Given this state of affairs, one can only choose for a long vowel in the non-diminutive singular if there is no allomorph with a short vowel available at all, i.e. LLLL. Note, trivially, that the LLLL pattern exists. Dutch has many stems with a long vowel for which no allomorph with a short vowel is available. Similarly, the SSSS pattern exists as well; Dutch has many stems with a short vowel for which no allomorph with a long vowel is available.

In sum, we actually understand on phonological grounds not only why some patterns do occur, but also why many patterns do not occur. These observations again strongly support the claim that Phonology does determine the selection of the allomorph for many of these cases. By now, we have a lot of descriptive adequacy to lose by assuming that all allomorph selection in Dutch simply happens to be listed. It is much more advantageous to propose that Phonology determines the allomorph distribution for the majority of cases, despite the fact that for some forms we have to assume listedness.

There is one pattern I have not discussed so far, viz. the SLSL pattern. The fact that this pattern is absent is not a theoretical necessity, but an accidental gap. As discussed earlier in Section 2.3 syntactic plurality in itself may select allomorphs or other irregular exponents. Yiddish, for example, shows allomorphy in plural contexts. In other words, it has an XYXY pattern (Lowenstamm 2007). In the following example the root kind ‘child’ alternates with its allomorph kinder in an XYXY fashion:

In short, an irregular exponent may be found in syntactically plural contexts. Similar data are found in Amharic (Kramer 2009).

Vowel length alternating nouns are not the only nouns that show stem allomorphy in Dutch. Just as in Yiddish, Dutch has stems that alternate between a simple form and an –er form.32 As in Yiddish, these nouns actually show an XYXY pattern:

Admittedly, these paradigms may sound slightly archaic to some speakers. Yet, crucially, it is very clear that even for these speakers the forms in the e-examples are illicit. The use of the allomorph in the singular diminutive is banned. This supports the claim that the allomorph is indeed determined by syntactic plurality for these examples.

Hermans and Postma (2009) argue that stem alternating words such as kind and vowel length alternating nouns belong to a specific noun class and that the additional morae in kinder and stems with long vowel express these noun classes in the presence of a syntactic plural head. Now, note, crucially, that vowel length alternating nouns never show the SLSL pattern, unlike the kind-kinder alternation. It is therefore unlikely that they should be analysed on a par. More generally, it is unlikely that the distribution of allomorphs is regulated by the syntactic plural head if the non-diminutive and diminutive plural forms do not show the same allomorph. I therefore set aside a syntactic account for the allomorphic distribution of vowel length alternating noun in Dutch, even though I concur with Hermans & Postma (2009) that the analysis is on the right track for the kind-kinder types. In short, syntactic plurality may determine allomorphy in Dutch. However, vowel length alternating nouns do not show this pattern.