What is the most controversial issue concerning bilingualism and age of acquisition?

4.1 Grammatical properties defining divergence

Researchers agree that these acquisition types differ in at least some properties. Yet the interpretation of the distinguishing features as either contingent or substantive is a matter of controversy that is complicated by the fact that not every difference is pertinent in this respect. Rather, variation indicating distinct acquisition types must be distinguished from individual variation and from variability due to L1 speakers’ multilectal competence that allows them to move in a linguistic variation space determined by situational, regional or sociolinguistic variables. I will not dwell on this issue, but I want to emphasise that it represents a methodological complication rather than a principled obstacle to attempts at identifying distinct acquisition types. That native speakers’ mental grammars are not fully identical (Dąbrowska 2012), is neither a new nor an original insight. Children acquire the grammatical properties underlying the PLD, and they are exposed to various lects, including idiolects; cf. Flores and Rinke (2020). Concluding from inter-individual grammatical variability that acquisition is not guided by universal principles is, however, a non sequitur, and guidance by Universal Grammar does not mean that inductive learning plays no role; cf. Meisel (2011b).

Keeping this in mind, let us first ask how L2 acquisition differs from L1 (monolingual) and 2L1 (bilingual L1) development. Summarising succinctly the vast amount of research on this topic, one can say that it is consensus that L2 differs substantively from L1. Whether these differences may be qualified as ‘fundamental’ is, however, a fundamentally controversial issue. Over the past 30 years, this debate focused on the role of Universal Grammar. Under the assumption that UG is the centrepiece of the LAD, it has been argued that crucial (2)L1–L2 differences can be accounted for as resulting from maturational changes to which the LAD is subject, entailing inaccessibility of parameterised UG principles at later AOA. Unfortunately, the UG-or-not-UG discussion has not clarified this issue. This is largely due to uncertainties about core theoretical notions like ‘UG’ or ‘parameter’, even within generative linguistics. It has allowed researchers to adapt these concepts to the needs of desired results. Rather than leading to an at least partial consensus, the discussion just petered out. Here, my intention is to characterise (2)L1–L2 differences in purely empirical terms, the idea being that this should hopefully suffice to reveal which of them qualify as fundamental ones.

The following non-exhaustive list enumerates properties in which the two acquisition types have been shown to differ. Note that none of these differences have been detected when contrasting L1 and 2L1 acquisition.

1. Acquisition-type-specific constructions.

2. Developmental sequences.

3. Clustering of superficially unrelated phenomena.

4. Developmental patterns: Rapid changes & variable use.

Table 2

Type-specific constructions.

Ad 1) Grammatical phenomena attested in some types of acquisition but not in others, e. g. in cL2 and aL2, but not in (2)L1 are likely to reflect differences in grammatical knowledge. The results of a study contrasting German L1 and 2L1 development with adult L2 acquisition can serve as an example; see Table 2, a slightly modified version of the one presented in Meisel (1991: 272).

At least two phenomena, subject-verb agreement and finite verb placement, both related to finiteness, can be argued to reflect qualitatively distinct grammatical knowledge in (2)L1 as compared to L2 learners. Subsequent research confirmed the claim that the acquisition of finiteness is a fast and virtually error-free process in L1, whereas it represents a major problem for L2 learners. In fact, placement of non-finite verbs in V2 position is never attested in (2)L1, but it is not uncommon in (c)L2. Similar results have been obtained by studies investigating the acquisition of finiteness in French; cf. Meisel (2009). Subject clitic pronouns (SCL) are finiteness markers in this language. Consequently, neither bilingual nor monolingual French L1 children ever combine SCL with non-finite verb forms; yet L2 learners use patterns of this type. Moreover, in French child language finite verbs precede negative pas as soon as they are used productively, whereas non-finite verbs follow it, i. e. SCL+V clusters are moved out of the VP. In L2 speech, on the other hand, finite V forms are attested before and after pas. Thus, finiteness and V movement are tightly connected in L1 development, whereas L2 is characterised by a dissociation of morphology and syntax.

Ad 2) This point refers to the fact that certain grammatical phenomena emerge in a strictly ordered sequence (Brown 1973). L1 acquisition is thus characterised by an ordered series of developmental phases, defined in terms of particular grammatical phenomena. These developmental sequences are invariant across learners, and they are strictly ordered in the sense that the order in which the phases are attained is not reversible. The underlying developmental logic is arguably grammatical in L1; see Meisel (2011b). In L2, on the other hand, other factors have been shown to intervene. Processability Theory, for example, explains it as reflecting increasing processing complexity; see Pienemann (1998).

Ad 3) The third phenomenon that can serve as a criterion identifying qualitative differences between acquisition types is commonly regarded as a property of grammatical parameters. Since parameters are defined at abstract levels of grammatical structure rather than in terms of surface properties, setting a parameter to a specific value typically causes a cluster of superficially unrelated grammatical properties to emerge simultaneously. This characterises earlier versions of parameters as well those referring to feature specifications of functional heads. Verb movement can again serve as an example. In languages like French or German where finite verbs are raised to CP and TP, respectively, they move over various elements, like negatives, adverbs, or quantifiers. A single operation thus triggers the emergence of a cluster of superficially unrelated phenomena during the same developmental phase in L1. In L2, they appear one by one, suggesting that they are learned separately.

Ad 4) L2 differs from L1 not only in the kinds of constructions used but also in how acquisition processes proceed. This difference manifests itself in two ways: a) In L1, one observes rapid changes of use, related to specific grammatical properties, whereas L2 is characterised by slow changes. ‘Rapid’ means that a phenomenon emerges within two or three months in a child’s speech. For example, a child acquiring German provides subject-verb agreement consistently, three months after the first verb is used and two months after agreement markers are first attested; cf. Meisel (2011b: 53–54) b) In L1, target-conforming forms and constructions are used consistently, once they are used productively, whereas in L2 the frequency of use of target forms oscillates (sometimes dramatically) in the course of acquisition of an individual and varies considerably across learners. Examples are the rapid increase of subjects and of finite verb forms, mentioned above.

In sum, empirical evidence gathered over the past 40 years allows us to conclude that first and second language acquisition exhibit qualitative differences that can justly be regarded as ‘fundamental’ in nature. Applying the differentiating criteria to simultaneous bilingualism reveals that 2L1 shares all the critical properties attributed to L1; it therefore deserves to be regarded as an instance of L1 development. Child L2, on the other hand, shares crucial properties with adult L2. This is not to deny that it differs from aL2 in other respects. Yet in view of the observed child-adult L2 commonalities, early successive bilingualism can be classified as a type of L2 acquisition if AOA happens at an age between 3;0 and 4;0 or later; cf. Meisel (2009).

4.2 Grammatical properties defining diversity

So far, the focus of this discussion has been on properties distinguishing acquisition types. I argued that certain differentiating properties that are not attested in comparisons of simultaneous bilinguals with monolinguals do emerge in contrastive studies opposing (2)L1 and (c)L2 speakers. This demonstrates the importance of AOA as a causal factor of divergence, and it corroborates current terminological choices according to which we are dealing with two distinct acquisition types, L1 and L2, each with two subtypes, L1/2L1 and cL2/aL2. Qualitative differences distinguish types, whereas subtypes share qualitative properties but can differ in others. It is this latter statement that needs further consideration, for it has been argued that certain properties attested in the speech of 2L1 children actually indicate partial acquisition failure, thus constituting qualitative differences as compared to monolinguals. Early AOA is a necessary but not sufficient condition for the development of a native competence. Under unfavourable conditions, children can fail in this task. The challenge is to specify the conditions that must minimally be met for children to be able to develop native competences.

Unfortunately, we are far from being able to meet this challenge, although considerable efforts have been made, over the past 20 years, to uncover effects of unfavourable learning conditions. Studies suggesting that bilinguals fail to acquire an L1 competence in one of their languages either investigated settings where one language is dominant and the other weak, or they analysed the speech of bilinguals who had not been exposed continuously to one of their languages, i. e. heritage language learners. Interestingly, the alleged cause of acquisition failure is in both cases a reduced amount of exposure to the target language. Disappointingly, however, neither of these two lines of research has as yet provided insights that might allow us to determine with some confidence when exactly children face the risk of acquisition failure. In order to be able to do so, it is necessary to distinguish between variability in language use and effects of grammatical divergence. In what follows, I will show why certain empirical facts cannot be interpreted as effects of changes in grammatical knowledge. To be clear, I am not denying that external factors like amount of exposure can result in grammatical divergence. Yet not just any noncanonical speech phenomenon counts as a valid piece of evidence supporting this conclusion.

The probably most frequently presented argument refers to frequency of use, mostly target-deviant uses by WL or HL speakers. Yet phenomena like rate of acquisition, frequency of occurrence, temporary preference for particular linguistic devices, etc., are quantitative differences not qualitative ones. Provided that a given construction is not omitted categorically, we must assume that the speaker’s grammar can generate it. Error rates, even if they are high, thus mean that learners have acquired this knowledge, but do not use it consistently. The task of acquisition research then is to explain why learners do not perform at the level of their competence. This is, however, of only limited interest for the definition of acquisition types.

Assessments of error frequencies nevertheless play an important role in studies of WL and HL speakers. Even the seminal WL studies by Schlyter (1993) or Schlyter and Håkansson (1994) rely strongly (though not exclusively) on this argument. According to their definition, a WL is characterised by slow acquisition rates and high variability in the use of the phenomena in question, ranging from non-existence to low frequency of occurrence. For example, Schlyter (1993) reports that Swedish-French bilingual children occasionally fail to place finite verbs in second position in WL Swedish. Table 3 presents some results obtained by Schlyter (1993) for three bilingual children (A, M, D) during various recording sessions (A2, A3, A4, etc.). The figures indicate frequency of use of a construction, i. e. “.5” in row *V3 means that 50 % of the verbs used during this session were incorrectly placed in third position.

Table 3

Frequency of V2 constructions in required contexts.

Importantly, as pointed out by Meisel (2007), this longitudinal study reveals that these children do not go through an initial phase characterised by a consistent target-deviant *V3 order (finite V placement in third position, e. g. Adverb-Subject-Verb). Yet only if this was the case, could one argue that the grammar of WL Swedish does not generate the V2 effect. In reality, all children studied use V2 as soon as contexts requiring it emerge in their speech, e. g. utterances with initialised adverbs. Crucially, the first V2 constructions appear simultaneously with (A) or before (D, M) the incriminated ones (*V3), and they are again attested in later recordings.

The only temporary failure to use V2 speaks strongly against the claim that these children acquired an L2 syntax of Swedish lacking the V2 effect. At any rate, if one was to explain *V3 as reflecting grammars without V2 properties, one would have to argue that WL grammars change repeatedly from +V2 to –V2 to +V2, a phenomenon never observed in L1 acquisition.

Emergence of noncanonical constructions is another criterion that has been suggested as a property distinguishing between divergent acquisition types. Some target-deviant constructions, like the just mentioned *V3 patterns, can possibly be explained as a result of transfer from the bilingual’s other language. Others, however, cannot be accounted for by transfer, e. g. so-called “unusual structures” (Döpke 1998, 2000). They are neither found in the speech of monolinguals of one of the languages, nor in balanced bilinguals, and they are for just this reason good candidates in the search for qualitative differences, as the following example cited by Döpke:

(1)

This construction is neither generated by the German nor by the English grammar. It deviates from the German target in that the finite verb follows the negator, *NEG Vfin instead of German Vfin NEG. Since the finite verb precedes the particle rein, it has been raised above VP; but it does not precede NEG and has thus not been moved above NEG, as required in German. In English, on the other hand, it would not have moved out of VP at all. Döpke does not offer a syntactic analysis. Yet citing uncommon utterances does not constitute sufficient evidence that WL/HL grammars differ from those of the stronger/majority language. Rather, one must specify properties in which the altered grammars differ from the target ones and show that the unusual sequence is indeed generated by a restructured grammar. At any rate, once again, developmental patterns reveal that the unusual structures do not reflect non-native grammars. They occur simultaneously with target structures, and they appear only temporarily and subsequently to a period during which the target structures are used productively.

The same objection must be raised against another alleged source of non-native properties in WL grammars, namely transfer from the stronger language. Yip and Matthews (2000), reporting on the acquisition of Cantonese and English by a bilingual boy, claim that wh-in situ is transferred from Cantonese to English. Yet the first occurrence of an English wh-utterance is one with the wh-word in initial position, and constructions with clause-initial wh co-occur with wh-in situ during the entire documented period of development. Consequently, the English option cannot have been replaced by the Cantonese one. Note that, as mentioned by the authors, the incriminated pattern also appears in monolingual speech. Thus, the observed pattern of use, with wh-initial constructions chronologically preceding and co-occurring with wh-in situ, suggests that the latter result from co-activation of the Cantonese grammar while processing English. Importantly, if one were to argue that properties of Cantonese syntax are incorporated into the English grammar, one would have to explain how the child could ever get rid of the Cantonese parts. Yip and Matthews (2000: 201) merely affirm that “they were unlearned gradually”. How unlearning works, remains mysterious.

From these observations on error rates, noncanonical constructions and transfer, I conclude that specific developmental patterns are a much more reliable criterion indicating qualitative differences between learner varieties. If both canonical and noncanonical uses are attested in the speech of bilinguals, and if the noncanonical ones emerge simultaneously or after the canonical ones, this cannot count as evidence of grammatical restructuring. Rather, the native option has not been altered, and bilinguals’ oscillation between two construction types should be regarded as a particularity of language use, possibly due to a failure of adequately inhibiting activation of the other language (Meisel 2007).

In sum, studies of bilingual settings in which one language exhibits WL characteristics have not yet provided convincing evidence supporting the hypothesis that WLs might develop as varieties that differ from native ones in core syntactic properties. Thus, although exposure to the PLD is significantly reduced, the degree to which this is typically the case for WLs of simultaneous bilinguals seems not to drop below a critical threshold. Rather, the amount of input still attains the minimum quantity necessary for the development of a native competence. The human LMC clearly is a robust device that makes language acquisition possible, even under unfavourable conditions. Nevertheless, there is, by logical necessity, a limit, a required minimum amount of exposure to the PLD. Unfortunately, we are currently not able to quantify this threshold. It remains to be seen whether relevant insights can be obtained by studying other bilingual settings where access to the PLD of one language is drastically limited.

This is why I do not want to conclude this discussion without having considered the possibility that heritage languages might offer the opportunity to gain the kind of insights required. As it turns out, results of HL research reveal a blurred picture of acquisition processes: The overwhelming majority of published HL studies are based on data that are of limited use when trying to decide whether early bilinguals fail to acquire native competences due to insufficient exposure to one of their languages. Firstly, from an acquisition perspective, the HL speakers studied represent a very heterogeneous group of learners. Secondly, assessments of amount of exposure are not based on first-hand studies of children’s interactions; they rather rely on retrospective self-reports or parental reports. Let me explain these two points of criticism.

Not only HL learners, HLs themselves are heterogeneous objects, for they have been studied from a variety of perspectives: sociolinguistic, educational, linguistic, each discipline applying different defining criteria. Some restrict the term to immigrant languages, others include indigenous languages, for some it is an L1 acquired either before or simultaneously with another language, for others it can also be a second language acquired in childhood. Not surprisingly, Ortega (2019) finds that even experts have difficulty defining the notion “heritage language”. What matters in the present context is that different learner types are subsumed under the label “HL learners”. The one point on which all authors agree is that the HL is the weaker language of bilinguals whose stronger one is the community language.

For our purposes, this lumping together of various types of learners, a common procedure in most HL studies that appeared over the past 15 years, is a serious problem. Recall that simultaneous and successive bilinguals differ in substantial ways if first exposure occurs at age 3-4 or later. Yet in the HL literature, 2L1 learners are habitually grouped together, either with successive bilinguals who grew up monolingually in the HL or with cL2 learners of the HL. The question therefore is whether we may reasonably expect these various types of learners to perform identically in using their HL. Let me remind you that a major goal of this paper is to characterise distinct acquisition types in terms of properties attested in their speech. Not only should members of one type share properties, some of these features must be type-specific, i. e. they should not appear in the speech of other types from which the one under discussion is to be distinguished.

The question thus is: Do HL learners constitute a distinct acquisition type? Concerning HL studies that generalise over heterogeneous groups of learners, the answer can only be negative. They do not i) present a set of linguistic properties uniquely characterising HL speakers while distinguishing them from other learner types; ii) decide whether specific features of HL speech are the result of incomplete acquisition[3] or of attrition of previously acquired knowledge; iii) determine which factors shape the language of HL speakers.

Ad i): The idea that HLs resemble in some respects L1s and in others L2s is not an insight enhancing our understanding of acquisition, unless it can explain in a principled way which L1 and L2 features can appear in HLs and which ones are excluded. As it stands, this claim covers all logical possibilities and is thus vacuous. Ad ii): The formula used in virtually all HL publications, stating that non-native features of HLs are due to “attrition or incomplete acquisition”, amounts to a renunciation of any attempt at explaining acquisition, for it implies that it is impossible to discover what can and what cannot be acquired by HL learners. Moreover, attrition does not mean that an individual’s grammar lacks a particular feature – it merely cannot be activated, and relearning differs crucially in rate and success from learning. The failure to distinguish between the two phenomena reflects the fact that these studies investigated adults rather than children. Still, at least in cases where exposure to the community language happened at age 5 or later, it should be possible to identify grammatical phenomena in the HL that have been acquired earlier. If HL speakers differ from monolinguals or balanced bilinguals with respect to these, attrition is a more plausible explanation than incomplete acquisition. Ad iii): Failure to distinguish learner types makes it impossible to decide whether HL particularities are due to learners’ AOA or to their reduced exposure to the target PLD. In fact, some researchers are entirely focused on insufficient exposure as a causal factor and do not even provide information on AOA, e. g. Albirini et al. (2011). Unfortunately, they do not specify what “sufficient” exposure means, either.

Fortunately, recent publications adopt a narrower definition of the term “HL”, allowing us to return to the question whether HLs reflect a distinct acquisition type, a claim explicitly supported by Benmamoun et al. (2013a). According to them, an HL is an L1, acquired either simultaneously with another language, or sequentially in early childhood, exposure to the other language occurring no later than at age 5. In spite of being an L1, the HL is said to exhibit L2 as well as L1 properties, i. e. learners develop partially “incomplete” or “divergent” knowledge. The reason why they do not attain a native competence in all grammatical domains of the HL is that the community language ends up being dominant.

In sum, according to the narrower definition, HL speakers are bilinguals who acquire the HL from birth and the other one simultaneously or successively, but no later than at age 5. But how, then, do HL learners differ from simultaneous bilinguals who develop two native competences? The surprising answer is: they don’t. In fact, Benmamoun et al. (2013b: 264) state that 2L1 children are “simply high proficiency heritage speakers”. This is tantamount to admitting that HL learners do not represent a distinct type, contrary to what these authors claim. They simply swap labels, postulating that 2L1 and HL learners are of the same kind, both subsumed under the HL label. The only differentiating criterion is that “the vast majority of heritage speakers do not show full acquisition of the heritage language” – although Benmamoun et al. (2013b: 264) explicitly state on the same page “that ultimate attainment of the heritage language is not relevant to the definition of an individual as a heritage speaker”.

I will not try to solve what is, in my understanding, a contradiction, nor will I be concerned with terminological issues. I object, however, to the idea that all bilinguals who speak a family language that is not the community language should be considered to be HL speakers. This would oblige us to regard virtually all bilinguals as HL speakers, for even bilingual societies do not consistently offer balanced bilingual domains in all situations of everyday life. What the suggestion by Benmamoun et al. (2013b) boils down to is that the crucial distinction is the one between high and low proficiency, and many or most HL learners are claimed to be low proficiency bilinguals. This means that they exhibit the same acquisition profile as unbalanced 2L1 learners who develop the family language as a WL. In other words, from a developmental perspective, research on HL acquisition addresses largely the same issues as those studying WL development. We are thus back at the claim that weaker languages differ from strong ones in core syntactic properties, although their speakers were exposed to both languages from birth. The particularity of HL learners is that exposure to the HL is said to have been significantly reduced, and this is argued to be the main causal factor resulting in such differences. Recall that the discussion of WL studies concluded that this hypothesis is plausible but that sufficient evidence supporting it has not yet been provided. The question then is whether HL research will be able to shed light on this issue. I will return to this issue in Section 5.

One problem on which recent HL research has made significant progress concerns the identification of grammatical features in which HLs conform to or deviate from their respective baselines; cf. Benmamoun et al. (2013a), Polinsky (2018) or Polinsky and Scontras (2020) for pertinent summaries. The list of phenomena in which language use by HL speakers differs from the baselines is impressive, yet it is difficult if not impossible to decide which ones, if any, qualify as telltale criteria identifying HL-particular varieties. One problem is precisely the wide range of phenomena identified by HL studies. It is not possible to highlight a set of features that appear in the speech of all learners, thus characterising HL unambiguously as distinct acquisition type. Nor is the reverse feasible, identifying features attested only in HL speech, not in other acquisition types.

What does emerge is that noncanonical constructions occur frequently, many resembling L2 uses. However, as the discussion of WLs has shown, frequency of noncanonical uses does not reliably indicate grammatical change, unless these constructions are used categorically. Still, we now do have a better idea about which features characterise HL grammars, for investigations are not limited, any more, to a search of noncanonical uses; they also study domains that are resilient to change, analyzing comprehension as well as production; cf. Polinsky (2018). According to the research summaries offered by Polinsky and Scontras (2020), many aspects of phonetics, phonology and syntax are particularly resilient. Inflectional morphology, on the other hand, is more vulnerable, nominal morphology more so than verbal morphology. They conclude that core properties of syntax are mostly unaffected; changes rather happen at interfaces between grammatical modules and especially at the syntax-discourse/pragmatics interface. This is a crucial point in the present context where the focus is on the conditions under which divergent developments are likely to happen, with a particular interest in triggers of changes in core syntax. However, although syntactic core properties belong to the most resilient grammatical domains, as expected, HL research suggests that they too can be affected, resulting in representational differences. Polinsky and Scontras (2020), for example, hypothesise that in HLs the available hierarchical structure is reduced. If this holds up, we are definitely looking at instances of divergent attainment – a finding that goes beyond what WL research showed.

Note, however, that we still do not understand the nature of divergent grammars. Much like other researchers before, Polinsky (2018: 25) concludes that HL speakers share properties with L2 speakers, but she insists that they are much closer to L1 speakers. In other words, HLs are not second languages, as insinuated by Rothman (2009). Still, characterising HL as an L1 containing (non-native?) L2 features is unsatisfactory, unless one can offer a principled account of the kind of L2 properties that can be part of an L1 grammar. Note further that we still do not know whether or when divergence is the result of incomplete acquisition or of attrition. Nor do we understand why or when core properties of syntax that are particularly resistant to alterations do change, after all.

This brings me finally to the second point of criticism mentioned earlier: although recent HL studies define HL speakers more narrowly, the large majority of them do not analyse interactions by children. Yet we may only hope to find answers to questions on the nature of divergent grammars if linguistic development of HL learners is investigated in longitudinal or cross-sectional analyses of quantified data, preferably collected in ongoing acquisition processes. Self-reports on within-family language distribution in HL speakers’ long past childhood will not do. Nor do self-ratings of proficiency or of language dominance provide the necessary data. In other words, studies on HL acquisition must meet the same methodological standards as first and second language acquisition research. So far, no more than a handful of the published HL studies meet this requirement, e. g. Silva-Corvalán (2018).