1.1 The notion of subject

The subject position, one of the oldest grammatical relation concepts, is a core grammatical function, “a significant ingredient in many of the grammatical phenomena of the language, so that it seems plausible to recognize it as a structural primitive” (Andrews 2007). Considerable evidence from many languages supports this claim, as demonstrated, for example, by the fact that subjects are more prone to what is called wh-movement cross-linguistically than other elements (Keenan & Comrie 1977). However, it is also a concept that has challenged linguistic theories of all flavors, especially those keen on identifying grammatical universals (Marantz 1982; Chomsky 2000), “as most languages have something which looks like a subject, but subjects differ across languages in their nature and properties” (Falk 2006). In fact, the notion of a grammatical subject is considered one of those grammatical phenomena that can be fully captured only when elements from different levels of grammar interface (Lambrecht 1994). The nature of subjecthood is not only controversial in terms of grammatical theory, but also in terms of definition and applicable criteria (Allerton 1980; Van Valin & LaPolla 1997). These criteria involve different linguistic domains, such as agency in semantics, topic-hood in pragmatics, and case in morphology (Lambrecht 1994). This is especially important in view of typological studies of ergative languages, where the subject of an intransitive clause such as The door slammed behaves like the object of a transitive clause (e.g., the door in John slammed the door). These studies underscore the need to expand the notion of subject beyond that typical of so-called nominative or subject-prominent Indo-European languages (Li & Thompson 1976; Schachter 1976; Dixon 1994). Against this background, we find it useful to adopt the widely-used, theory-neutral, typologically motivated terminology (Comrie 1978; Dixon 1979), which defines three syntactic relations in the clause:

Thus, subjecthood in nominative-accusative alignments is a grammatical relation expressing S and A, but not O. Two major phenomena indicate the existence of grammatical subjects (Andrews 2007): (i) overt, consistent structural features such as word order, case marking, and assignment of agreement; and (ii) less consistent, behavioral phenomena that are more abstract and less equivocal, usually relative to other grammatical phenomena. These indications are especially relevant to Hebrew, where two word orders prevail, with differing degrees of subjecthood (Ravid 1995; Melnik 2006).

1.2 Grammatical subjects in Modern Hebrew

Despite the massive syntactic changes Hebrew has undergone over its long history (Givón 1977; Bendavid 1988; Borer 1995; Shlonsky 1997; Hatav 2000; Doron 2005), its Semitic origins are still apparent in its rich morphology, including subject-verb agreement (Berman 1978; Ravid 1995; Schwarzwald 2002). While the current study focuses on syntactic phenomena, verb agreement is relevant here as grammatical subjects can be either lexical or pronominal, including pronominal omission. The issue of subject realization and omission in Hebrew is vastly studied in the literature, mainly in the context of pro-drop discussions. For example, it was shown to be related to accessibility (Ariel 1998), licensing (Borer 1989), and information structure (Melnik 2006). However, the prototypical behavior of subjects in Modern Hebrew can be generalized as shown in Tables 1 and 2. Tables 1 and 2 show the Hebrew agreement system regarding finite (past, present and future tense) main verbs, in terms of type of agreement (Table 1: number, gender, and person), and the options for pronominal omissions (Table 2).

Past and future verbs agree with their subjects in person, number and gender, while present tense verbs are marked only for number and gender agreement (Table 1). Pronominal subject omission is generally possible in 1^st and 2^nd person pronouns in past and future tense, and is prototypically not allowed in all other positions (Table 2). Hebrew may allow third person pronominal omission in some restricted contexts, such as adjunct subordinate clauses, with a particular semantic types of verbs (Melnik 2007), or in some accessibility related scenarios (Ariel 1998). In the following sections, we exemplify the main patterns of subject realization in Modern Hebrew.

1.3 Grammatical subjects in spoken interaction

A context-bound study that takes dialogical conditions into account has been proven relevant in many cases, especially in accounting for the emergence of pragmatically dependent elements (such as the emergence of pronouns, conversational contexts containing turn-taking, interaction, and third party reference). These, and other interactive phenomena utilize triadic or polyadic skills not used in dyadic contexts (Forrester 1988). Deixis forms, for example, may be learned through overhearing, and so does understanding of naming practices (Brener 1983; Oshima-Takane 1988).

In adult-child conversation, adult interlocutors use scaffolding procedures to clarify and interpret children’s utterances, while making the meaning of their own language forms accessible to the child by basing them in shared context or linking them to previous discourse. Thus, adults provide children with models of how their intentional meanings should find conventional expression (Murase et al. 2005; Howard et al. 2008).

The context of the current analysis is the natural conversation of Hebrew-speaking preschool and school children with their age peers, rather than with their caregivers. Peer talk offers a unique window on development, as children in peer interactions do not receive elaborate adult feedback facilitating linguistic communication (Blum-kulka et al. 2010; Schuele 2010). Therefore, peer interactions provide more realistic distributions of language structures and reliable information on linguistic usage (Hoff 2010; Veneziano 2010; 2018). Peer talk moreover renders children active participants in communicative events, tasked with expressing intentions and meanings to their interlocutors while taking into account their discursive roles (Forrester & Cherrington 2009). As conversational agents, children participate in the construction of communicatively valid behaviors and are placed upfront for observing and treating those of the more experienced partner (Snow & Ferguson 1977; Gallaway & Richards 1994). Furthermore, utterances in conversation might have different roles. That is, an utterance can initiate a conversation (or a section within one), or it can function as a response to a previous utterance by an interlocutor. Utterances can also be structured based on previous utterances, thus resonating them (Du Bois 2007). These qualities of utterances provide children with different opportunities to manifest their involvement in conversation, taking into account that each type of utterance has a different function. We assume children’s emerging conversational skills go hand in hand with grammatical acquisition (Serratrice 2005), making peer talk a particularly felicitous framework for studying the development of grammatical subjects.

1.4 Seeking grammatical subjects in development

Despite its obvious importance in the acquisition of syntax, the developmental literature does not contain an abundance of studies looking into the emergence and consolidation of grammatical subjecthood. Grammatical subjects make their appearance in child language investigation under three main umbrellas. One perspective, prevalent in the generative framework, focuses on subject slots as empty categories (De Villiers 1995), especially in relation to the agent and patient roles. According to de Villiers, the inventory of possible lexical NPs in the language is paralleled by a set of empty categories, which need to be learned (or parametrized) by the child, given the different syntactic and lexical properties in different languages. The acquisition problem according to this view is for the child to determine this inventory and the syntactic conditions under which empty categories are allowed. The omission of pronominal subjects by young children, termed null subjects (e.g., want water) has thus been a central topic of generative acquisition studies, explained as either due to children having different grammatical abilities than adults (Borer & Wexler 1987; Clahsen 1990; Valian 1991), or assuming an extended period where English allows null subjects (Hyams & Wexler 1993). Bloom (1993) strongly supports the parametric view, whereby children start off representing overt subjects as obligatory (as in English), but as a result of simple positive input – subjectless sentences in the speech of adults – children who are exposed to a null subject language can switch their grammars to pro-drop (as in Italian or Spanish, see Shin 2016) or topic-drop (as in Chinese). Finally, in Hebrew-specific perspective, Armon-Lotem (2008) regards the acquisition of the Hebrew finite verb as related to the morphosyntactic features of the subject of the sentence. She examines the emergence of verb morphology together with overt subjects in the speech of several Hebrew-speaking children from about 1;6 to 3 years of age. This study indicates that Hebrew number, gender and person marking first appears towards the end of the second year of life, while bare subjects first occur much earlier; however, no distributional evidence is offered.

A second perspective on learning grammatical subjects regards it as part of the acquisition of the verb’s argument structure (Tomasello 1992; Gleitman & Gillette 1995), as a window on children’s growing knowledge of verb semantics and tendency towards agentive structures (Matthei 1987; Brooks & Tomasello 1999; Alishahi & Stevenson 2008). These studies mainly focused on the number and type of verb complements across early development, frequency and meaning of specific constructions, and implications for learning (Bidgood et al. 2014; Ambridge & Blything 2016), including impaired populations (Fletcher & Ingham 1995). For example, Goldberg (2006) considers the verb as having more predictive value than the grammatical subject in generalizing argument structure constructions for learners. However, no study to date has systematically investigated the evidence for the consolidation of grammatical subject structures and functions from early to the later preschool years.

A third approach to learning grammatical subjects focuses on children’s early ability to detect the pragmatic and discourse conditions for subject realization and omission, as shown by, e.g., Allen (2000) for Inuktitut, and by Guerriero et al. (2001) for Japanese. One insight is that in languages with fixed word order, such as English, children rely on word order and pragmatic knowledge in comprehending active transitive sentences, whereas in languages with more flexible word order, the primary source of information about the agent/subject role is verb agreement (Abbot-smith & Serratrice 2015; Serratrice & Allen 2015). Important to our current topic, Paradis & Navarro (2003) show that the sources of information available to young native learners regarding subject realization at the pragmatics/syntax interface include both distributions of overt and null subjects in the ambient language as well as the specific events that children experience in on-going interaction. Paradis and Navarro show that, in line with other studies of Spanish and Catalan acquisition (Grinstead 1998), monolingual children in their study grasped the appropriate frequency and the functional discourse-pragmatics determinants of subject realization in Spanish at two years of age. This conclusion is shared by Salazar Orvig et al.’s 2010 study of clitic pronouns in dyadic conversations, who suggest that children’s uses of pronouns reflect early pragmatic skills, acquired by the third year of life. They also suggest that the grammatical values of morphological devices are not acquired prior to their discursive value, but rather these pragmatic functions are associated with the grammatical level from the onset. Finally, peer talk studies of children aged 12–34 months demonstrate how children build and co-construct grammar dialogically in terms of the social-interactive projects they are trying to accomplish, negotiating how they stand vis-a-vis one another (Goodwin & Kyratzis 2012; Köymen & Kyratzis 2014).

Within these three perspectives to the development of grammatical subjects, previous research mostly examined isolated parameters. Consequently, research questions regarded the study parameter as a dependent variable, asking what affects its realization. For instance, the realization of the subject (as lexical vs. pronominal vs. zero, Serratrice 2005), or the development of a specific argument structure construction, can be studied in this way. However, engaging in language is an inherently multifactorial, context sensitive, social activity. That is, parameters do not evolve in isolation. Thus, the current paper proposes an integrated approach to the development of grammatical subjects, seeking for usage patterns that capture the contextual conditions for each type of grammatical subject in different constructions. In that we follow Croft’s (2001) radical approach to grammatical phenomena, and suggest that the grammatical subject is not a unified notion. Rather, it is built bottom-up on a construction-specific basis. By revealing the subject-related usage patterns associated with each age group, we will be able to portray a picture of the developmental path through which such exemplar-based grammatical category is created, and a non-unified, probabilistic notion of grammatical subject is formed. Since the notion of subject is a multi-faceted phenomenon with relevance to morphological, syntactic and discourse-pragmatic information, we analyze its occurrence in children’s peer-talk conversations across preschool ages, using cluster analysis to reveal multifactorial usage patterns. We expect to find usage patterns which are sets of utterances, grouped together according to statistically based within-cluster similarity and between-cluster dissimilarity. We hypothesize that the distribution of usage patterns in the corpus will not be uniform across age groups, such that each usage pattern will characterize a particular age range in the data. That is, for every age range there should be a usage pattern that is used significantly more frequently than others. Thus we will be able to characterize each age range in terms of its usage patterns of grammatical subjects. In order to so, we utilize the notion of Discourse Profile Constructions.

1.5 Form, function, and Discourse Profile Constructions

Language use is inherently contextual, concrete, and discriminatory (Ramscar et al. 2010). Form and function, therefore, are intimately related, in the most obvious way, especially in the case of grammatical form (morphology and syntax).¹ A verb in the past tense form, for example, has the function of construing a state of affairs that took place in a time before the time of speech. Such construal is mostly connected with narrative discourse. On the other hand, a verb in the future tense form has the function of discussing the future; that is, it is used to predict, plan, and convey intentions. In the same way, a subject in the first person plural form has the function of talking about the interlocutors as a unified entity, and a subject in the second person singular has the function of profiling the interlocutor as a topic in the current discourse. Thus, form is more than isolated, context-free morphology or syntax; form is always motivated by function, to the extent that morphemes, words, and sentences have meanings. That is, there is a functional (i.e., meaningful) difference between a first person plural pronominal subject and a first person singular subject, and there is a functional difference between a verb in the past form and a verb in the present form.

Such an approach to language use and language function as highly concrete stems from the Usage-Based approach to language, in which language knowledge, as well as linguistic phenomena, are the product of praxis. The Usage-Based view can be traced back to Wittgenstein who put forward the proposition that, for many cases, “the meaning of a word is its use in language” (Wittgenstein 1953). Usage, however, is a very fluid concept. Taking the notion of usage seriously, then, we need to adopt a model that is able to quantify the role of usage in building language knowledge. The Discourse Profile Construction hypothesis is such a model (Dattner 2019). Discourse Profile Constructions (henceforth, DPCs) are a manifestation of this view in accounting for the usage from which the meanings, or the functions, of grammatical constructs emerge. DPCs are emergent form-function correlations that consist of multiple sources of concrete formal and functional information, conventionally pairing a usage pattern of clauses with a unified construal or discursive function. A usage pattern in this context is a frequent co-occurrence of concrete elements of form and function (e.g., a first person singular subject and a past tense verb), realized as a cluster of tokens with high within cluster similarity and high between cluster dissimilarity. Moreover, Dattner (2019) shows that DPCs are extensions of the Construction Grammar notion of Argument Structure Construction (Goldberg 1995; Perek 2015). From a usage-based, discursive point of view, Argument Structure Constructions can be broaden to include concrete forms and functions, emphasizing the existence of basic discursive scenarios that correspond with concrete exemplars of usage patterns.

Note that other models try to answer the question of what is a possible sentence in a language, or “to what extent is the human faculty of language an optimal solution to minimal design specifications, conditions that must be satisfied for language to be usable at all” (Chomsky 2001). The approach taken in the present paper assumes that for modeling the grammar of a language the question should be why does the speaker choose the concrete form A over form B to convey a construal of the world X. Thus, the DPC hypothesis states that DPCs are the basic clausal form-function correlations in the language, constituting the main usage-based source from which grammatical meaning emerges. Consequently, the DPC hypothesis does not account for what can be done with language; rather, it accounts for what is done with language.

3.1 Cluster analysis: Subject-related usage patterns

A Hierarchical Clustering on Principal Components analysis suggested an optimal division of the utterances in the data into five clusters. The optimal number of clusters was chosen according to growth of inertia, such that the difference in explained variation between dividing the data into four versus five clusters is greater than the difference between dividing the data into five versus six clusters. The cluster dendrogram is presented in Figure 1, and a description of each cluster according to the categories that were mostly associated with it is given bellow, summarized in Table 5.

Figure 1

Hierarchical Clustering on Principal Components, colors indicating 5 clusters of the 5,694 sentences in the corpus: cluster 1 in olive-green, cluster 2 in green, cluster 3 in red, cluster 4 in light blue, and cluster 5 in purple.

Cluster one comprised 846 tokens, which were 14.85% of the 5,694 utterances in the data. It is a multifactorial usage pattern, mostly associated with initiated utterances containing a first person plural pronominal subject and a future tense verb (see Table 5 for a description of category distributions). It has the functions of (i) profiling the at-the-scene peer group as a single entity (hence the first person plural), and (ii) planning, suggesting and conveying intentions (hence the future tense verb). The following is a representative example for cluster one:

Cluster two was the largest cluster of tokens in the data, comprising 3,054 utterances, constituting 53.63% of the utterances in the data. It is a usage pattern associated mostly with second person singular pronominal subjects, initiated and response utterances, with present tense verbs, and less so with first person singular. These characteristics are coupled with the functions of (i) highlighting the role of the interlocutor in the current state of affairs, and (ii) interpreting and commenting on current situations:

Cluster three consists of 475 tokens, which are 8.34% of the utterances in the data. This usage pattern is mostly associated with post-verbal lexical subjects, resonating utterances, and present tense verbs. Each of these forms is a marker of a particular function: The present tense verb marks the function of commenting on current state of affairs, and the post-verbal subject is used to introduce an out-of-the-scene entity to the discourse (hence the use of a lexical subject, see Ariel 2004).

Cluster four was very small, consisting of 60 tokens, which are 1.05% of the utterances in the data. It was mostly associated with post-verbal lexical singular subjects in repeating utterances. This form, as was the case in cluster three, is linked with introducing a new entity into the discourse, as in the following:

The usage pattern realized as cluster five consists of 1,259 tokens, constituting 22.11% of the utterances in the data. It is mostly associated with post-verbal (plural) lexical subjects, present tense verbs, in initiated utterances. The main difference between cluster five’s usage pattern and the usage pattern of clusters three and four is the role of the utterance in the conversation. While clusters three and four consists of resonating and repeating utterances (respectively), cluster five’s usage pattern is linked to initiated utterances. Such utterances constitute a more natural place in the discourse for introducing new entities, as in:

In the following section we will look at the distribution and correspondence of each usage pattern with regard to age groups.

3.2 Usage patterns in the development of the grammatical subject as a grammatical category

The cluster analysis presented above was done without taking into account the association of each utterance with a specific age group. That is, for the purpose of the cluster analysis, the tokens in the data were considered to be a homogeneous corpus of 5,694 utterances, each coded for the same set of categorical variables. This allowed us to reveal usage patterns in the data regardless of the speaker’s age. However, given each token’s identification and cluster, we were able to conduct a post-processing analysis, looking for correspondences between cluster-based usage patterns and age groups. Figure 2 presents a Correspondence Analysis of age group and clusters.

Figure 2

Post-processing using Correspondence Analysis: clusters and age groups.

The Correspondence Analysis map in Figure 2 depicts a clear developmental path in terms of similarity between age groups, expressed in shared cluster-based usage patterns of the grammatical subjects in the data. The youngest age group is located distantly relative to all other age groups, indicating that 2 year olds share very few usage patterns with the older children. Half a year older, the 2;6–3;0 children are more similar to the 3;0–4;0 and 4;0–5;0 age groups than to the 2–2;6 group. The 4;0–5;0 group is located a little higher on the map, due to its higher usage-based similarity to the older children in the corpus. And finally, the 5;0–6;0 and 7;0–8;0 groups are located near each other, with the 5;0–6;0 group functioning as a bridge between the 4;0–5;0 and the 7;0–8;0 age groups. That is, based on shared usage patterns of grammatical subjects in conversation, we can detect a gradient of three developmental stages in the preschool years: (i) 2;0–2;6 year olds, (ii) 2;6–5;0 year olds, and (iii) 5;0–8;0 year olds.

This developmental path can be further examined by the usage pattern that mostly corresponds to each group. Note, however, that “mostly corresponds” does not mean “exclusively used”: all usage patterns can be found in all age groups at some frequency. Rather, a characterization of an age group according to a usage pattern is based on a scalar, probabilistic distribution. The following sections present the developmental path of the grammatical subject usage patterns as realized by the correspondence analysis.

3.3 Usage patterns as Discourse Profile Constructions

Pairings of usage patterns and discourse functions, like the pairings revealed in our results, are described by Dattner (2015; 2019) as constituting Discourse Profile Constructions. Discourse Profile Constructions (DPCs) are emergent form-function correlations that consist of multiple sources of formal and functional information, conventionally pairing a usage pattern of clauses with a unified construal or discursive function. DPCs are claimed to be the basic clausal form-function correlations in the language, and to constitute the main usage-based source from which grammatical meaning emerges (Dattner 2019).

Three DPCs emerged from the data regarding the use of grammatical subject in conversation. Note that the labels for the DPCs are ad-hoc in that they are built bottom-up. That is, it is not the case that there is a predefined inventory of DPCs in the grammar of the language, such that the child needs to acquire it. Rather, DPCs are probabilistic clusters of similar usage events. Thus, only if a set of tokens are linked to a single discursive function frequently enough, and this function has discriminatory and discursive importance, a DPC will emerge. Importantly, these DPCs are relevant to a conversational type of linguistic interaction. In other types of linguistic data (e.g., in written expository texts, or in child directed speech by parents) different DPCs might emerge with regard to the use of grammatical subjects, that will join the heterogeneous category of subjects in Hebrew.

The first DPC is the joint action planning DPC, emerging from the tokens of cluster one: initiated utterances with a pre-verbal, first person plural pronominal subject (S/A) and a future tense verb, as in:

This is a pattern of grammatical features (constituting both form and function), that serves a discursive function within conversation: it is used to plan joint actions, with reference to the interlocutors as a unified group of agents. According to the present corpus, this DPC is frequently used only from age 3;0 and up.

The second DPC is the basic conversational narrative DPC, emerging from the tokens in cluster two: pre-verbal 1^st and 2^nd person singular pronominal subjects (S/A), in present and past tense, in both initiated and response utterances:

This pattern is used to serve the communicative function of describing current actions, commenting on past events, and telling narratives, while identifying each of the interlocutors as an agent and keeping continuous conversational topics. That is, it is a usage pattern composed of concrete usage events in which these grammatical features and functions corresponded with each other. The central location of this usage pattern on the CA map in Figure 2 is an indication to its wide use by all age groups in the data, except for the youngest 2 year olds. That is, it is a basic conversational pattern of initiation and response, concerning the interlocutors themselves (in 1^st and 2^nd person singular), for commenting and narrating in present tense, or a hypothetical past tense (showing a well developed inflectional system and the use of adverbials such as suddenly or one moment to enhance the pretend situations):

The third DPC identified here is the conversational presentation DPC, emerging from the tokens of cluster five: post-verbal lexical subjects (mainly S) with verbs in the present tense:

This pattern is used to introduce new topics to the discourse and to refer to less accessible entities outside of the conversational arena. Importantly, we show the learning curve of this DPC: The youngest children use it mostly with repeating utterances (cluster 4). That is, they are not introducing new entities, but rather repeating the presentation of such by their peers (as in (12) above). The mid-range children use this DPC mainly in resonating utterances (cluster 3). That is, while not repeating, they still re-use an immediately available structure:

Finally, the older groups appropriately use this DPC in initiated utterances (cluster 5). That is, once presented to the discourse, an off-stage entity (the star in (29) bellow) becomes accessible and is further referred to using a pronominal object.

Summing up the discussion of our results, we see that each usage pattern serves a particular communicative function. Importantly, note that each function can potentially be served by other grammatical features as well. However, we show that each function is prototypically served by a single usage pattern, which is a combination of morphological, syntactic, semantic and pragmatic information. This is a concrete, discourse-oriented, probabilistic view of the links between form and function in language, made possible by assuming a similarity based categorization of grammatical notions realized as Discourse Profile Constructions.

The associations between DPCs and age groups demonstrate the development of the grammatical subject category as a heterogeneous, exemplar-based category (Abbot-Smith & Tomasello 2006) vis-a-vis conversational skills: At the young age of 2;0–2;6 years, Hebrew-speaking children hardly relate to their interlocutors, and hardly keep track of a coherent topic, hence the use of the usage pattens of clusters 3 and 4. That is, they do not engage in conversation. Conversation begins to sprout at the age of 2;6 years according to the present corpus, with the mid-range ages referring mainly to themselves and their interlocutors as subjects (cluster 1, and to some extent cluster 2). Full command of conversation appears only in the older groups of 5;0–8;0 years old, realized as a non-restricted use of usage patterns, and command of all types of subjects within the grammatical subject category. The older children in the corpus talk about real as well as hypothetical events, in which both them or their interlocutors may be realized as subjects, as well as entities which are not part of the speech event itself. This suggests a less restricted discourse, containing reference to the interlocutors and to the off-stage scenario, presenting entities to the discourse and maintaining them, initiating conversations as well as responding, planning, commenting, and telling narratives. The present study thus shows that distributional information of multiple factors is important for categorization, facilitating the learning of the grammatical subject category (c.f. Romberg & Saffran 2010).