Keeping track of referents in discourse requires monitoring which referents are new and which referents are given. In English, for example, a discourse referent can be marked as new through the use of an indefinite article (e.g., This morning we saw a fox in the garden), and later be marked as given by using a pronoun or a definite article (e.g., When it saw us, the fox got scared and ran away). Languages vary in the way in which they mark new and given referents, not only in form (e.g., whether they use articles or other discourse markers with the same function) but also in optionality (i.e., the degree to which the use of markers to signal a certain discourse function is optional or obligatory). By their very nature, optional discourse markers are used less consistently than obligatory ones, resulting in greater variability in the input that children receive. As a result, optionality has been found to affect children’s acquisition of discourse markers, with obligatory markers emerging earlier than optional ones (Berman & Slobin, 1994; Hickmann et al., 1996). Here we studied children’s production of discourse markers across four typologically-distinct languages, which differ in the degree to which the marking of new and given referents is optional: English, Hindi, Mandinka and Spanish (with samples collected in the United Kingdom, India, The Gambia and Spain, respectively).1

The main aim of this study was to investigate the effect of optionality on children’s acquisition of discourse markers. More specifically, we were interested in a particular type of optionality: that observed during a process of grammaticalization. For instance, the diachronic process whereby numerals are grammaticalized into indefinite articles (e.g., when the Old English form for ‘one’ gave rise to the indefinite article a in modern English) has been documented in many different languages (see Givón, 1981). However, from the point in time when the numeral ‘one’ starts being used to introduce new discourse referents until it becomes an indefinite article that must be used obligatorily with the same discourse function (Heine, 1997), the use of this form remains optional. Generalizing what we know from the language acquisition literature (e.g., Slobin, 1985; Berman & Slobin, 1994; Hickmann et al., 1996; Hickmann & Hendriks, 1999; MacWhinney, 2001; Narasimhan & Dimroth, 2008), we hypothesize that the acquisition of optional markers undergoing a process of grammaticalization should be protracted relative to fully grammaticalized markers.

A potential process of grammaticalization of the numeral ‘one’ into an indefinite article has recently been identified in Chinese (Chen, 2004; Wong, 2016) and Polish (Hwaszcz & Kędzierska, 2018). Here we investigated the case of Hindi, which, like Chinese and Polish, does not have an article system, but allows for the use of the numeral ‘one’ to introduce new discourse referents (Kachru, 1980, 2006; Dayal, 2004, 2018; Sharma, 2005). Based on a linguistic analysis of diachronic change and Hindi semantics, our starting assumption was that Hindi is undergoing a process of grammaticalization of their numeral ek into an indefinite article. However, the goal of this study was not to test this assumption, but rather to investigate the effect of optionality on children’s acquisition of discourse markers, understanding grammaticalization processes as a special kind of optionality.

To this end, children’s and adults’ use of the Hindi numeral ek to introduce discourse characters was compared with the use of indefinite articles in English and Spanish (which is obligatory for the same discourse function), and the use of bare nouns in Mandinka. Like Hindi, Mandinka also lacks articles, but to the best of our knowledge, it does not use the numeral ‘one’ (kiiling) for reference introduction, offering another interesting comparison with the use of ek in Hindi. Regarding the marking of familiar referents, this is obligatory in all four languages, which vary in the grammatical forms available for this discourse function. The second experiment in the study exclusively focused on Hindi, extending the initial investigation to older children and two additional locations in Northern India.

Previous studies on the early stages of acquisition of the new/given distinction focused on spontaneous production in young children’s speech (see Hickmann et al., 2015). However, studies focusing on later stages of development recognized the importance of eliciting child data in extended discourse, as it allows for a greater range of variation in referential strategies (for a review, see Berman, 2015). In particular, third-person narratives have been frequently used because they allow researchers to test the development of appropriate forms of reference for different functions. Bamberg (1986, 1987) identified three discourse functions in narratives: (i) introductions for new characters, (ii) maintenance for referents that have been mentioned in the immediately preceding context, and (iii) reintroduction for referents that have been mentioned before but not in the immediately preceding context.

Cross-linguistic studies have found that children as young as 3 years use pronouns appropriately for character maintenance (Hickmann & Hendriks 1999; Vion & Colas, 1999; Wong & Johnston, 2004). These studies also showed that young children rarely use pronouns to introduce new characters, opting for indefinite and definite nominals to mark that function. However, they often use pronouns inappropriately for character reintroductions, resulting in ambiguous reference. Findings from studies of naturalistic dialogue in various languages confirm the above observations (e.g., Orvig et al., 2010), with some studies reporting appropriate use of light forms (including overt and covert pronouns) for reference maintenance as early as in the two-word stage (Serratrice, 2005; Hughes & Allen, 2013). By the age of 2;5, English-speaking children also demonstrate sensitivity to discourse structure in disambiguating pronominal reference by interpreting pronouns as referring to the most prominent character, even when only the first mention and subject status of the noun are used to establish its prominence in the preceding context (Song & Fisher, 2007).

Findings from cross-linguistic studies of reference in extended discourse also report an early sensitivity to discourse continuity and the use of appropriate forms for familiar characters by the age of 4, whereas new characters are not introduced appropriately before the age of 7, and character reintroduction is not mastered until age 10 (Hickmann et al., 1996; Hickmann & Hendricks, 1999). In conclusion, the results of previous studies suggest the following order of acquisition of discourse functions in narratives across languages: Maintenance > Introduction > Reintroduction. Interestingly, the same order of acquisition of discourse functions has been reported in studies of second language learning (e.g., Jarvis, 2002; Sharma, 2005).

Wong and Johnston (2004) argue that the order of acquisition of the three discourse functions results from the different cognitive demands that they pose on the speaker, as speakers must maintain a mental model of the ongoing discourse in order to keep track of the listener’s knowledge (Levelt, 1989). In their view, introduction and maintenance require information about the listener’s knowledge to be updated, but reintroduction makes a further demand: that the listener’s focus of attention be monitored. Thus, according to Wong and Johnston (2004), young children may be familiar with the appropriate linguistic forms for reintroduction (e.g., definite articles), but their failure to track the listener’s attentional focus leads to inappropriate referencing.

A close comparison of the acquisition of appropriate markings for the three discourse functions across typologically-distinct languages reveals that the linguistic properties of the systems also play a role in acquisition. Some markings operate directly on the noun phrase and are therefore known as local markers (e.g., articles in English), while markings operating at the sentence level are known as global markings (e.g., in Chinese, all new referents occur in post-verbal position). Hickmann et al. (1996) investigated the acquisition of discourse markers in English, French, German and Chinese and observed that optional local markers of newness are infrequent in all the languages included in their study until 5 years of age. Interestingly, the obligatory global markings emerged later than the optional local markers in Chinese, becoming frequent by age 7. Hickmann et al. (1996) argue that the delayed acquisition of global markings (even when obligatory) is due to their functional complexity since there is no one-to-one mapping between sentence position and discourse function (see also Slobin, 1985; MacWhinney, 2001; Narasimhan & Dimroth, 2008).

In a more recent study, Aksu-Koç and Nicolopoulou (2014) compared children’s use of local and global markings to differentiate new and given referents in three languages: Greek, English and Turkish. Their findings show that children as young as 3 predominantly used indefinite forms for character introductions in Greek, but they did not do so until the age of 5 in English (which has a morphologically poorer article system, while Greek has a bundle of co-occurring features supporting the formation of form-function relations) and also in Turkish (which uses global markings).2 Thus, while obligatoriness may facilitate marker acquisition, global markings appear to be particularly difficult to acquire, even when they are obligatory.

Children’s use of referential forms in narrative-elicitation tasks can also be influenced by the previous discourse and by the listener’s perceptual access to the pictures. English-speaking children as young as 2;5–3;5 years old are sensitive to the type of question used in narrative elicitation (e.g., What is X doing? vs. What is happening?; Campbell et al., 2000; Matthews et al., 2006). Cross-linguistic studies have also reported that children show a developing sensitivity to the interlocutor’s perceptual access to the pictures, using light referential forms more often when they are narrating the story to an interlocutor who has perceptual access to the pictures, than when the interlocutor is ignorant (Hickmann et al., 1996; Serratrice, 2008). However, this is a late emerging sensitivity and is only systematically observed at around age 9.

The present study focused on local markings in the four languages we investigated and examined the role that optionality plays in the acquisition of those markings. Since previous work suggests that obligatory local markings emerge by the age of 3 (Berman & Slobin, 1994) and optional local markings are frequently used by the age of 5 (Hickmann et al., 1996), we compared 5-year-olds’ use of discourse markers of newness and givenness to their adult counterparts across the four languages in our study. In addition, because previous studies report earlier sensitivity to discourse structure than to the interlocutor’s perceptual access, in this study we used a general event-focus question – ‘What is happening here?’ – to elicit narratives in contexts with shared perceptual access between the participant and the experimenter.

Relative to previous cross-linguistic studies, our work aims to deepen our understanding of the effect of optionality on the acquisition of discourse markers by focusing on the grammaticalization of the Hindi numeral ek into an indefinite article, and comparing reference introduction in Hindi to other languages with and without indefinite articles. To the best of our knowledge, this is the first study to treat grammaticalization as a stage of optional use of the emerging form, therefore exploring the implications of diachronic change for language acquisition.

Language acquisition studies normally adopt a synchronic viewpoint, treating languages as fixed systems that young children must acquire through exposure. However, we know from diachronic linguistics that languages are constantly in flux (Heine & Kuteva, 2006). Thus, studying the acquisition of discourse markers in languages where articles are in the process of being grammaticalized sheds light on how optionality affects the acquisition of discourse markers, while providing us with an opportunity to study language change synchronically.

In his investigation of the development of the numeral ‘one’ into an indefinite article in Israeli Hebrew, Givón (1981) characterizes this process of language change as universal, having been independently attested in Germanic, Romance, Mandarin, Sherpa, Hungarian, Neo-Aramaic, Persian, Turkish and various Amerindian and Austronesian languages, in addition to being a hallmark of all Creole languages (p. 35). Heine (1997) proposed five stages in the process of grammaticalization of the numeral ‘one’ into an indefinite article: (i) the word ‘one’ is only used as a numeral; (ii) it is used to introduce characters in the discourse; (iii) it is used to mark specific indefiniteness; (iv) it is used to mark non-specific indefiniteness; and (v) it is completely grammaticalized as an indefinite article occurring with all types of nouns.

Since character introduction occurs early in the process of grammaticalization, languages at this stage do not yet mark new discourse referents obligatorily, resulting in children receiving an inconsistent input. Of the four languages in our sample, English and Spanish require the use of indefinite articles to introduce new discourse characters, whereas Hindi lacks an article system. However, Dayal (2018) has recently argued that the numeral ek ‘one’ can be used to introduce new discourse referents in Hindi and is frequently used with that discourse function, although it does not satisfy diagnostic semantic tests for indefinite articles (Chierchia, 1998; for discussion, see Dayal, 2018). While Dayal’s semantic analysis of ek confirms that it is not an indefinite article, it is important to note that the relative frequency with which it is used to introduce discourse referents in Hindi is open to empirical investigation. Compatible with Dayal’s synchronic analysis, here we assume that Hindi is in the second stage of Heine’s (1997) grammaticalization scale (i.e., the numeral ‘one’ can be used to introduce new discourse characters), and investigate (a) the frequency with which ek is used with that narrative function by both adults and children, and (b) how optionality affects the acquisition of this discourse marker relative to languages with indefinite articles, such as English and Spanish.

The fourth language in our sample, Mandinka, is similar to Hindi in that it does not have an article system, although it has a numeral ‘one’ (kiiling) which could in principle be used to introduce new discourse referents (as it has been recently reported in other languages without articles, such as Chinese (Chen, 2004; Wong, 2016) and Polish (Hwaszcz & Kędzierska, 2018)). The comparison between Mandinka and Hindi is also interesting because both The Gambia and India were British Colonies and many schools are English-medium. Since language contact is an important driver of language change (Heine & Kuteva, 2006), if the numeral ‘one’ was being grammaticalized as an indefinite article in Hindi or Mandinka, this process could be related to the contact of those languages with English (although this hypothesis was not tested in our study).

It must be noted, however, that Mandinka is an under-studied language and it has therefore not been documented whether their numeral ‘one’ is used to introduce new discourse referents. This would not be a surprising development, given the universality of this particular instance of language change (Givón, 1981). Therefore, the present study investigated the possible emergence of an indefinite article in Mandinka, in comparison with Hindi.

Finally, while indefinite articles tend to emerge from the numeral ‘one’, the universal path for the emergence of definite articles starts with exophoric demonstratives, which evolve into anaphoric demonstratives and later into definite articles (see Greenberg, 1978; Lyons, 1999). Amongst the languages in our sample, English and Spanish have fully grammaticalized definite articles, whereas, to the best of our knowledge, anaphoric demonstratives in Hindi and Mandinka are not undergoing a process of grammaticalization into definite articles. Therefore, our investigation of the use of markers of familiarity in these four languages will not look at the effect of grammaticalization. However, we will return to the grammaticalization of definite and indefinite articles and their connection to common ground management and Theory of Mind development at the end of the paper (see also Rubio-Fernandez, 2020).

Below is a brief description of the referential systems of the languages included in our study:

English

English is a West Germanic language with default SVO order, which is fairly rigid and can be used to express grammatical relations between arguments. Regarding the new/given distinction, English has a grammaticalized article system, with indefinite articles being mandatory to introduce new referents, and definite articles marking given referents. There is no gender or number agreement in articles. Demonstratives can also be optionally used to mark givenness, and they are only marked for number. Given referents are also signaled by the use of pronouns, which have number agreement. In addition, third-person singular pronouns establish a three-way gender distinction (she/he/it). Bare nouns are used for mass nouns (e.g., rice or water) and for generic readings of plural nouns (e.g., Tigers live in jungles). However, singular bare nouns are grammatical in very few contexts by comparison (e.g., location (John is on television) or coordination (Kate ate with knife and fork)). Global markings like subject-verb inversions are also used in certain contexts to mark newness, but they are less frequent (e.g., Dancing in the rain was a girl).

Hindi

Hindi is an Indo-Aryan language spoken in the Indian subcontinent. It has a relatively free word-order with SOV as the default. Word order is associated with information structure and all major constituents can be scrambled. Sentence initial noun phrases generally refer to given entities in the discourse and new entities occupy immediately preverbal position. Nouns scrambled to the sentence initial position get definite interpretation (Kidwai, 2000).

Hindi does not have an article system, but optional local markers (such as numerals, demonstratives and case marking), as well as optional global markings (such as word order variations) can be used to mark the givenness of a referent. The latter possibility, however, is limited to specific syntactic constructions (with inanimate referents in direct object position) and is not generally available for every utterance. Third person pronouns are marked for number in some dialects of Hindi, but are not marked for gender, and can be used as demonstratives. The verb is inflected for gender agreement with the subject or the object depending on the construction type. Pronouns can be dropped in subject position.

Bare nouns usually have a definite interpretation in Hindi. However, in specific contexts, such as the direct object position (1) and locative constructions (2), bare nouns get an indefinite reading (for discussion, see Dayal, 2018):

Of the available optional local markers, the numeral ek ‘one’ is the most frequently used for marking new referents and it has even been claimed that it is required to introduce discourse characters (Dayal, 2018), although this claim has not yet been empirically tested.

Mandinka

Mandinka is a Mandé language spoken in The Gambia and Senegal, amongst other West African countries. It has a rigid SOV order and lacks an article system. A nominal marker –o, which has sometimes been called a default marker, occurs obligatorily with most nouns. However, in certain contexts, such as negative or interrogative clauses and NPs including a numeral, the default marker -o can be dropped, and its absence impacts the meaning of the NP. The following is an example from Creissels (2012a) illustrating the interaction between –o marking and negation in Mandinka (note that musu + lexical marker -o > mus-ôo; PF = Perfective):

Historically, the lexical marker -o evolved from the demonstrative woo. Creissels (2012a, 2012b, 2020, forthcoming) argues that at some point in the evolution of the language, -o probably marked definiteness but lost that function over time (for a classic study of this pattern of language change in other African languages, see Greenberg, 1978). Nowadays, the default marker -o does not mark (in)definiteness.

Demonstratives ñǐŋ ‘this’ and wo ‘that’ can be optionally used in Mandinka to mark given information. An indefinite determiner dóo ‘some’ is also available, but it is not frequently used for reference introduction. The third-person pronoun (à) does not encode gender or animacy and cannot be omitted in subject position. Unlike the other three languages in our sample, Mandinka does not have an extensive written tradition.

Spanish

Spanish is a Romance language with SVO order, although it is not as rigid as English. Spanish has grammaticalized articles that are inflected for gender and number. It is obligatory to use indefinite articles to introduce new discourse referents (e.g., Compramos una casa ‘(We) bought a house’), and definite articles (e.g., Compramos la casa ‘(We) bought the house’) or pronouns (e.g., La compramos ‘(We) bought it’) are used for familiar discourse referents. A 3-way demonstrative system (este/ese/aquel) can be optionally used to mark givenness, and like articles and pronouns, demonstrative forms are inflected for gender and number. Generics are expressed with the use of the definite article (e.g., Los tigres viven en la jungla ‘[The] tigers live in the jungle’), unlike in English (which uses bare plural nouns). Bare nouns are rarer in Spanish than in English, with only mass nouns (e.g., Necesito café ‘(I) need coffee’) and plural count nouns (Compré flores ‘(I) bought flowers’) being allowed in direct object position. Spanish is a pro-drop language and pronouns in subject position are therefore often omitted.

As the above descriptions suggest, the four languages in our study vary in the forms available to mark discourse functions, as well as in their optionality. Given this variability, we focused on the most frequent forms used by adult native speakers of each language to introduce discourse characters and maintain reference in folk narratives elicited during pilot work. In the actual study, we compared children’s and adults’ use of indefinite articles as obligatory markers of newness in English and Spanish, Hindi’s optional use of the numeral ek with the same discourse function, and Mandinka’s use of bare nouns bearing the default lexical marker -o. While this lexical marker does not signal (in)definiteness (unlike indefinite articles and the numeral ‘one’ in the other languages), bare nouns were the most frequent form used by adult native speakers of Mandinka to introduce discourse characters during pilot work and were therefore coded as the appropriate form for reference introduction in the study.

The relative optionality of the newness markers coded in these languages is therefore the following: Hindi > English > Spanish > Mandinka. Hindi does not have any obligatory markers to introduce new discourse referents but does optionally use certain markers with this function. This makes newness marking more inconsistent in Hindi than in the other languages. English and Spanish both have obligatory article systems, but English has more permissible uses of bare nouns (in specific constructions) compared to Spanish. Finally, according to the available documentation (see Creissels, 2012a, 2012b, 2020, forthcoming), Mandinka lacks obligatory newness markers and employs a default lexical morpheme for all nouns. It must be noted, however, that Mandinka is not as well documented as the other languages in our sample, and it is therefore possible that Mandinka speakers use their numeral ‘one’ to introduce new discourse referents due to the influence of English (especially in the case of children, who are schooled in English).

In contrast with the marking of new discourse referents, marking familiar referents is obligatory in the four languages in our sample. Indeed, English, Hindi, Mandinka and Spanish all have pronouns, which are used for reference maintenance. In addition, English and Spanish have definite articles that are used to mark given discourse referents, while Mandinka uses demonstrative determiners and Hindi uses bare nouns with the same discourse function – as documented in pilot work. Therefore, for the marking of familiar referents, we compared children’s and adults’ use of definite articles in English and Spanish, Hindi’s use of bare nouns, and Mandinka’s use of demonstrative determiners. In addition, we compared the use of pronouns for reference maintenance in the four languages.

Regarding the marking of familiar referents, it is interesting to note that speakers of all four languages in the study had at least two options (e.g., using a pronoun or a definite article in Spanish). However, this is different from Hindi speakers’ arbitrary choice between marking and not marking new discourse characters (i.e., using ek plus a noun vs. a bare noun). Whereas pronouns and definite articles, or pronouns and demonstratives all signal familiarity, their use is not always interchangeable (with different researchers distinguishing the use of these forms in terms of salience, prominence, or accessibility; e.g., Ariel, 1990; Gundel et al., 1993; Arnold, 1998). However, to the best of our knowledge, the variability observed in Hindi speakers’ use of ek for reference introduction does not depend on information structure, and reflects, instead, a genuinely optional choice on the part of the speaker, which we predict should delay its acquisition relative to obligatory forms in other languages.

The optionality of the available discourse markers varies across the four languages in our study, which allowed us to test the Optionality Hypothesis: the acquisition of optional markers is protracted relative to obligatory markers, as suggested by numerous cross-linguistic studies (e.g., Berman & Slobin, 1994; Hickmann et al., 1996; Hickmann & Hendricks, 1999; Serratrice, 2005; Schaeffer & Matthewson, 2005; Guasti et al., 2008; Rozendaal & Baker, 2008; Hughes & Allen, 2013; Bassano, 2015). While the use of ek to introduce new characters is optional in Hindi, the use of indefinite articles with the same discourse function is obligatory in English and Spanish, while Mandinka lacks a specific marker for reference introduction (with speakers using the lexical marker -o as a default). In contrast with the differences in optionality observed for reference introduction, marking familiar characters is obligatory in all four languages. It must be noted, however, that each language has different grammatical means to mark familiar referents, and the above studies have also documented differences in the acquisition of different givenness markers (e.g., pronouns are acquired earlier than definite articles, even though both signal familiarity).

On the basis of the Optionality Hypothesis, and given the grammatical characteristics of the referential systems of the languages investigated, we made the following predictions:

The first experiment revealed that 5-year-old Hindi-speaking children marked new characters less frequently than English- and Spanish-speaking children of the same age. Hindi has the option of using the numeral ek ‘one’ to introduce discourse characters, but it does not have a fully-grammaticalized indefinite article (Kachru, 1980, 2006; Dayal, 2004, 2018). The diachronic process whereby numerals are grammaticalized into indefinite articles has been documented in many languages (see Givón, 1981; Lyons, 1999), and our starting assumption was that Hindi is currently undergoing the same process. Such a grammaticalization process is compatible with Hindi-speaking adults using the numeral ek less frequently than Spanish- and English-speaking adults use the indefinite singular article to introduce new characters, which in turn explains the protracted acquisition of this discourse marker in Hindi-speaking children.

Experiment 2 had two main aims. The first was to further explore the developmental trajectory of ek acquisition. In this regard, we were interested in the age at which Hindi-speaking children would demonstrate adult-like use of the optional marker ek. According to MacWhinney (2001), children’s acquisition of a form-function mapping should be influenced by the frequency of its input, so we expected Hindi-speaking children to acquire the character-introduction function of the numeral ek later than children speaking languages with obligatory newness markers. Given that children have acquired the most sophisticated referential devices in a language by age 10 (e.g., the ability to appropriately reintroduce characters using definite articles; Hickmann et al., 2015), we tested a group of 10-year-old Hindi-speaking children from the same school in Delhi to see whether their use of ek in the narrative task was comparable to that of adults.

Second, the protracted acquisition of the numeral ek as a newness marker is compatible with the assumption that the Hindi numeral is undergoing a process of grammaticalization into an indefinite article. However, the results of Experiment 1 are also compatible with an alternative, more parsimonious hypothesis: the use of the numeral ek to introduce new discourse referents may be characteristic of a dialectal variety of Hindi spoken in the Delhi area.3 This is an important research question because previous analyses of the use of ek for reference introduction may have been based on speaker intuitions or observations for the dialectal variety of Hindi spoken in Delhi, or other similar dialectal varieties (e.g., Dayal, 2004, 2018; Sharma, 2005). The second aim of Experiment 2 was therefore to try to replicate the results of Experiment 1 outside of the Delhi area. To this end, the same narrative-elicitation task was used again in Experiment 2 with 5-year-olds, 10-year-olds and adults from Gorakhpur, a city in the North Eastern state of Uttar Pradesh, and with adults from Allahabad, a smaller city in the same Indian state.

In addition to the two main aims described above, Experiment 2 also had a secondary goal related to the first aim of the experiment (i.e., exploring the developmental trajectory of ek acquisition). Here we were interested in investigating the individual patterns of ek use produced by 5- and 10-year-old children and adults in Delhi and Gorakhpur. Using miniature artificial languages in the lab, Hudson Kam and Newport (2005, 2009) showed that 5- to 7-year-old children regularized the use of determiners even when receiving an inconsistent input, while adults learned determiners veridically, producing them according to their frequency in the input. The results of Experiment 1 confirmed that the use of ek to introduce new characters is not systematic in Hindi. However, unlike Hudson Kam and Newport, we do not have a way to assess the relative exposure of each age group to this novel use of the numeral ‘one’. Nevertheless, while our study lacks the experimental control of artificial language experiments, it offers naturalistic production data, which we believe is equally important in understanding language change and its implications for language acquisition. Experiment 2 therefore investigated whether Hindi-speaking children reveal more regular patterns of ek use than adults – either using it systematically to introduce new characters or never using it, in line with the lab results of Hudson Kam and Newport (2005, 2009).

In order to investigate the effect of optionality on children’s acquisition of discourse markers, we elicited picture-based narratives from both children and adults in four different languages. However, while visual narratives are generally presumed to be highly accessible (and thus used in children’s books, comics, assembling instructions, etc.), research suggests that the interpretation of images as sequential events is an acquired skill that requires exposure and practice (Cohn, 2019, 2020). Thus, differences in cultural background (e.g., between cultures with a strong oral story-telling tradition vs. a picture book tradition) could result in the interpretation of each image as an isolated event rather than a continuous story. This lack of continuity would in turn affect the way in which characters are referred to, as the same character might be treated as a new referent in each picture and be marked accordingly (Fussell & Haaland, 1978; Cook, 1980; Núñez et al., 2012). Since Mandinka has a strong oral story-telling tradition, but not such a strong picture book tradition, our participants may have interpreted the images on the computer screen as disconnected pictures, which would explain why both children and adults used -o-marked bare nouns for both new and familiar referents, despite having the option of using demonstratives and pronouns for reference maintenance.

A quick look through The Gamble Archive (1946–2003), which is a rich collection of work on the history and culture of The Gambia by Professor David Gamble (1997), shows that the use of pronouns is actually very common in Mandinka. This led us to investigate whether the lack of pronouns in our data was due to the specific task employed for eliciting narratives. We hypothesized that the reason why Mandinka speakers used full nominals for all characters was because they were not adopting a narrative stance. Interestingly, we observed a similar pattern of behavior in 3 English-speaking adults, who also treated the pictures as independent events and repeatedly referred to familiar characters using an indefinite article (see Figures 3 and 4). In order to investigate whether the lack of pronouns observed with Mandinka speakers in Experiment 1 was due to the use of an unfamiliar task, we collected oral stories from a small group of native speakers of Mandinka without any pictorial prompt. Given the cultural significance of story-telling in West Africa, re-telling of oral narratives should reveal a more naturalistic use of pronouns than picture story-telling.

According to Hickmann et al. (2015), cross-linguistic comparisons are necessary before generalizations can be made about early vs. late mastery of reference on a universal basis (p. 204). In this study, we investigated a typologically-diverse set of languages, allowing us to explore the effect of optionality on the acquisition of different discourse markers for two main narrative functions. Our initial prediction regarding the acquisition of newness markers was that they would be influenced by the consistency with which they are used in adult language (MacWhinney, 2001). Our results confirmed that the use of discourse markers emerged earlier in languages that consistently used them for the same functions. As predicted, children produced the most adult-like descriptions in Mandinka, given the uniform use of -o-marked bare nouns in adult responses. Hindi-speaking 5-year-olds, on the other hand, demonstrated the least adult-like performance, which was also expected given that Hindi-speaking adults are the least consistent in their use of newness markers amongst the four language groups. Results from Spanish and English also fell in line with our predictions, showing that children in both of these languages use appropriate newness markers (i.e., indefinite articles) in a more adult-like way than Hindi-speaking children.

Regarding the use of givenness markers across languages, our results revealed a significant effect of age in the use of various givenness markers, including, most importantly, a lesser use of definite articles by English- and Spanish-speaking children. By contrast, our results did not reveal a developmental difference in pronominal use between children and adults, a pattern that was expected since previous studies have shown that children as young as 3 years old are able to use pronouns for character maintenance, while 5-year-old children already demonstrate adult-like performance (Wong & Johnston, 2004; Song & Fisher, 2007).

Regarding cross-linguistic differences in the use of givenness markers, when comparing English and Spanish, Spanish-speaking children revealed the most adult-like performance when marking familiar characters. This pattern of results can be explained by the different consistency with which articles are used in the two languages: Spanish has more restrictions on the use of bare nouns than English does, which results in Spanish-speaking children arguably getting exposed to a more consistent use of articles. The relatively infrequent use of bare nouns in Spanish would therefore facilitate children’s form-to-function mapping between articles and discourse functions (see also Bassano, 2015). Overall, the results of our study support the Optionality Hypothesis, according to which the acquisition of optional discourse markers is protracted relative to obligatory markers.