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date: 19 April 2021

First-Language Acquisition of Morphologyfree

  • Dorit RavidDorit RavidDepartment of Communications Disorders, Tel Aviv University

Summary

First-language acquisition of morphology refers to the process whereby native speakers gain full and automatic command of the inflectional and derivational machinery of their mother tongue. Despite language diversity, evidence shows that morphological acquisition follows a shared path in development in evolving from semantically and structurally simplex and non-productive to more complex and productive. The emergence and consolidation of the central morphological systems in a language typically take place between the ages of two and six years, while mature command of all systems and subsystems can take up to 10 more years, and is mediated by the consolidation of literacy skills. Morphological learning in both inflection and derivation is always interwoven with lexical growth, and derivational acquisition is highly dependent on the development of a large and coherent lexicon. Three critical factors platform the acquisition of morphology. One factor is the input patterns in the ambient language, including various types of frequency. Input provides the context for children to pay attention to morphological markers as meaningful cues to caregivers’ intentions in interactive sociopragmatic settings of joint attention. A second factor is language typology, given that languages differ in the amount of word-internal information they package in words. The “typological impact” in morphology directs children to the ways pertinent conceptual and structural information is encoded in morphological structures. It is thus responsible for great differences among languages in the timing and pace of learning morphological categories such as passive verbs. Finally, development itself is a central mechanism that drives morphological acquisition from emergence to productivity in three senses: as the filtering device that enables the break into the morphological system, in providing the span of time necessary for the consolidation of morphological systems in children, and in hosting the cognitive changes that usher in mature morphological systems in both speech and writing in adolescents and adults.

1. Introduction

Explaining how children acquire morphological systems in their native tongue has been of interest in developmental psycholinguistics since its inception (Brown, 1973; Cazden, 1968; Slobin, 1985–1995). The domain of morphology involves the internal structure of words, and as such it interfaces with phonology, the lexicon, syntax, and semantics (Bybee, 1985). As a result, morphology serves as a major arena for testing hypotheses and theories about language acquisition, processing, and use (Hay & Baayen, 2005; McLelland & Patterson, 2002; Pinker & Ullman, 2002), especially regarding the regular/irregular split in inflection (Lignos & Yang, 2016; Marcus et al., 1992). Accounts of morphological learning mainly seek to explain children’s path from a limited beginning with many errors of both omission and commission to full and automatic command of the inflectional paradigms in a given language. Fewer studies have looked at the acquisition of derivational morphology, although children begin acquiring derivational patterns as early as in their third year of life (Clark, 1993, 2016), especially in languages with rich morphological systems (Vainio, Pajunen, & Häikiö, 2019). Fewer studies still have monitored the long and protracted process of morphological development, stretching into adolescence, that interacts with the growth of the literate lexicon in written language (Berman, 2007; Seidenberg & Gonnerman, 2000). The current article takes an inclusive view on the process and nature of first-language morphological acquisition across languages with different typologies. It thus describes the learning of inflectional and derivational morphology by native-speaking toddlers, children, and adolescents, mostly in speech, but also in writing, including literacy effects.

The article is constructed as follows. It starts with a review of the two accounts of inflectional learning, which contextualizes the most studied domain of morphological acquisition in current linguistics and psycholinguistics. Next, it considers current methodologies in investigating morphological acquisition in production and comprehension. The next section on factors in morphological acquisition reviews (a) input patterns in the ambient language, including the notion of frequency; (b) target-language typology; and (c) the central topic of development from morphological emergence to productivity. This latter part is presented in three phases: “starting small” (morphological emergence, including diminutive mediation and initial morphological markings; growing paradigms), morphological proliferation, and taking control (the consolidation of morphology during the school years, including derivational acquisition and writing morphology). Together, these three phases trace the developmental paths in different languages of the two major morphological components of inflection and derivation (Bauer, 2004). This article concludes with a short note on morphological learning by children.

2. The Debate on Acquisition of Inflection

We begin with the question of how children learn inflectional morphology in their native tongue. This section has two goals. First, it serves to introduce and contextualize the topic of morphological acquisition before elaborating on its various components. Second, inflectional morphology, as demonstrated in this section, has served as a testing ground for the major linguistic theories of our time.

Inflection is the semantically transparent and predictable, obligatorily applicable component of morphology expressing grammatical notions and relations (Booij, 2006; Bybee, 1985). Across languages, inflection generally marks the expression of number, gender, and case in nouns, temporal and modality categories in verbs, and agreement of other categories with nouns (Dressler, 1989). The acquisitional task children face thus involves the formation of paradigms containing inflected word forms that express these notions and relations. As such, the acquisition of inflectional morphology is dependent on the developing content-word and function-word lexicon, and on children’s emergent understanding of syntactico-semantic relations in the phrase and the clause. Inflectional morphology is characterized by low-type frequency (a small number of inflectional markers) and extremely high-token frequency in usage. For example, in languages which mark distinctions of tense, every utterance that includes a verb will be marked inflectionally for this category, just as every noun or article will be marked for gender if the language distinguishes this by obligatory inflection. Therefore, children start marking inflections early on, toward the end of the second year of life, at the same time they start stringing words together (Berman, 1981; Bittner, Kilani-Schoch, & Dressler, 2003; Clark, 1993; Stephany & Voeikova, 2009). However, the road to the automatic production of inflectional word forms in full paradigms in first-language acquisition presents learning challenges due to the abstract character of inflectional categories and the often irregular and opaque form of many inflectional markers (Clark, 2016; Ravid, 1995).

As an obligatory, highly frequent category, marking relevant distinctions in language, inflection is the first morphological category to emerge (Diessel, 2015; Slobin, 1985–1995). Given its critical role in the growth of lexicon and syntax, much of the psycholinguistic literature has targeted the acquisition of inflection in order to account for morphological learning in particular and language acquisition in general. Specifically, English noun plurals and past-tense verbs have been of interest to child language researchers ever since it was first demonstrated that English-speaking children could produce nonce past-tense and plural forms in the Wug test (Berko, 1958). Both plural and past-tense systems contain regular (car-s, jump-ed) and irregular (man/men, teach/taught) items. The literature shows that after the initial use of a small number of frequent forms around their second birthday, preschool children go on to produce correct and overgeneralized inflected forms such as hold/holded (Brown, 1973; Dressler, 2011; Elsen, 1997; Kuczaj, 1977). Overgeneralization is gradually abandoned in favor of the conventional inflected forms attained toward entry to elementary school (Maslen, Theakston, Lieven, & Tomasello, 2004).

To explain the acquisition of inflection, two contrasting accounts have been offered (Tatsumi & Pine, 2016).The theory-based approach termed “Words and Rules” assumes that the inflectional divide in English represents an epiphenomenon of the innate design of the human language faculty (De Villiers, 1985; Pinker & Ullman, 2002). According to this dual-route view, inflection requires gaining command of two systems—lexicon and grammar (Marcus, 1995; Marcus, Brinkmann, Clahsen, Weise, & Pinker, 1995). It assumes that regular forms are computed in the grammar by productive, categorical, top-down symbolic operations that assemble morphemes and simplex words into complex words and larger syntactic units. Regular forms, the default units in inflection, are produced by all-or-none combinatorial rules that are not affected by semantic class, extralinguistic contextual factors, or memory factors such as frequency. By contrast, irregular forms are acquired and stored like other words in the lexicon, with the plural grammatical feature incorporated into their lexical entries (Marcus et al., 1992). Unlike regular forms and syntactic structures, words are governed by the principles of associative memory. In adults, a stored inflected form blocks the application of the rule to that form, but elsewhere the rule applies to any item with the appropriate symbolic category (Pinker & Prince, 1992). Acquiring inflectional morphology under this account would start with memorizing regular and irregular inflected forms in the input. With maturation, syntactic rules apply, resulting in both correct and overgeneralized forms, as young children do not yet have deep memory traces of all irregular forms. With time and exposure to more input, lexical entrenchment and blocking increase until overregularizations disappear, testifying to a mature dual-route mechanism of words and default rules (Boloh & Ibernon, 2013; Clahsen & Fleischhauer, 2014).

This deterministic, deductive treatment of inflectional learning regards the full paradigm as a goal that the child needs to acquire, given innate, language-dedicated tools. However, knowledge of full paradigms is more typical of linguists, and is required of foreign language learners using meta-linguistic strategies. In natural language, lemmas are not “saturated,” that is, they do not occur in the same corpus with all of their inflectional members (Ackerman & Malouf, 2013; Chan, 2008). Emergentist, usage-based approaches show that this situation is accentuated in child-directed speech and child speech, which underscore the distributional trends of adult language (Shirai, 2015): what is available to children is highly frequent, child-oriented words, some of which are inflected, depending on lexical class and language typology (Ravid et al., 2008). Young children thus have to build up their inflectional systems in an “unsupervised” manner from missing, sparsely inflected forms in the ambient language (Lignos & Yang, 2016). According to the usage-based, emergentist approach, native-speaking children construct inflectional systematicity, like all facets of language, from experience with individual usage events in a process that is graded, probabilistic, interactive, context-sensitive, and domain-general (Goldberg, 2006; Tomasello, 2003). Inflectional productivity emerges gradually, beginning with concrete items and repeating sequences in the child’s input (Abbot-Smith & Tomasello, 2006; McCauley & Christiansen, 2019). This approach proposes a single-route model to handle both regular and irregular inflectional morphology by a probabilistic network which learns the relationship between stems and their inflected forms under constant pressure from linguistic input (McClelland & Patterson, 2002; Plunkett & Marchman, 1993), whereby previous experience yields item-based schematic representations resulting in grammatical regularities (Bybee & Slobin, 1982; Köpcke, 1998; Slobin & Bever, 1982). Performance is conditioned by linguistic experience, improving over many learning trials in a developmental process. Overgeneralization takes place given the similarity of the exemplar being learned to others already stored and taking into account frequency factors (Aguado-Orea & Pine, 2015), as morphological patterns are learned as generalizations over memories of words (Racz, Pierrehumbert, Hay, & Papp, 2015).

In recent years, studies have made it possible to examine the two approaches in typological, developmental perspective, offering empirical and theoretical insights on the debate between symbolic, top-down versus item-based, usage-based accounts of morphological learning (Ramscar, Dye, Blevins, & Baayen, 2018). One is that in languages with several inflectional classes, such as Italian, Spanish, or Welsh, the dual-route model does not make the right predictions, nor do results show across-the-board, rapid learning (Gathercole, Sebastián, & Soto, 1999; Orsolini, Fanari, & Bowles, 1998; Thomas & Gathercole, 2007). Evidence from typologically divergent languages supports the view that learning of inflections is a complex task that is dependent on a range of different factors and the interplay between them. These include general cognitive abilities such as pattern recognition and generalization; cognitive properties of the data, such as transparency, regularity, consistency, and salience; linguistic structure, phonological and syntactic, as well as semantic content; and contextual factors such as frequency and predictability. For English, where the dichotomous regular/irregular debate originated, Matthews and Theakston (2006) showed that children’s error rate in producing noun plurals and past-tense verbs depends, inter alia, on the frequency of the word and paradigm size, as well as on the phonological similarities between stems and stem/inflected form pairs. Smolík (2014), working on a corpus of child English, showed a consistent effect of imageability facilitating the acquisition of noun plurals. For German, a language with seven different plural markers, Laaha, Ravid, Korecky-Kröll, Laaha, & Dressler (2006) did not find a single regular/default plural in children’s experimental elicitations: the most important factor affecting acquisition was the morphological productivity of the plural class. Similar results were found by Szagun (2001). In Danish, input frequency factored in the acquisition of noun plural marking (Kjarbak, dePont Christensen, & Basbøll, 2014). In Arabic, a Semitic language with two regular and one irregular (broken) class of plurals, Ravid and Hayek (2003) found that semantic properties of the noun (agent/non-agent) were responsible for fast versus very slow acquisition rates of feminine and masculine regular plurals, respectively; and Saiegh-Haddad, Hadieh, and Ravid (2012) found frequency effects in the correct production of all Arabic plural types, regular and irregular.

To conclude this section, consider three studies on the acquisition of adjective agreement with nouns in typologically different languages—Spanish, Lithuanian, and Hebrew. The study of Spanish acquisition (Mariscal, 2009) showed that children construct abstract agreement categories based on a dynamically changing confluence of sources in the input, such as noun phonology and the shape of determiners, pronouns, and adjectives. The study on Lithuanian agreement (Savickiene, Kempe, & Brooks, 2009) found that children make use of the mediating factor of diminutive morphology in learning to mark adjective agreement. The study on Hebrew (Ravid & Schiff, 2012) showed that the path to learning adjective agreement involved the graded extraction of increasingly finer generalizations about Hebrew noun plurals from lexical experience—including gender marking, types of stems and stem changes, and conditions for irregular suffixation. All three studies interpreted their results as supporting a single-route model of inflection, showing that children store representations of units of various sizes, and form generalizations at differing degrees of abstraction—rather than applying a rule to all members of a symbolic category.

This presentation of the debate on inflectional learning served to introduce the centrality of morphological acquisition to linguistic and psycholinguistic research. The next section discusses the canonical methods used to obtain empirical evidence in the field of morphological acquisition.

3. Methodological Issues

Psycholinguistic evidence for language acquisition development is obtained through various classical, well-tested, and innovative methods of child language elicitation and natural data collection. The oldest of these is in the form of diary case studies, most often recorded by a parent observer, as in the case of Melissa Bowerman’s unpublished diary of her two daughters, Eve Clark’s extensive examination of the development of derivational morphology based on diary studies (Clark, 1993), or the book by Esther Dromi (1987) on the early lexical, pre-grammatical development of her Hebrew-speaking daughter. Diary studies provide rich contextual background to the data recorded, most of them by parents or close relatives. Linguist parents can be relied on to note major developments in their children’s lexicons, including the first occurrences of inflections and word formation. For example, I noted my daughter Sivan’s first inflection (the imperative feminine verb kxi “take!”) at 1;7 in my (unpublished) diary data. However, except for the one-word stage, diary studies cannot record all of the child’s productions and so tend necessarily to be selective, focusing on interesting, new forms in child language. Therefore, diaries can indicate developmental stages and point at major phenomena in acquisition, but they are not representative of the statistical patterns characterizing parental and child productions

A second source providing researchers with information regarding children’s initial lexicons and grammars are parental report questionnaires, the best-known of which is the MacArthur-Bates CDI (Communicative Development Inventories; Fenson et al., 2007; Silva et al., 2017). While limited to early development, this form of investigation has been adapted to over 60 languages and cultures and is widely used to assess early language skills in large samples for establishing population-based norms. For example, a recent survey of European Portuguese and Galician used an adapted form of the CDI to determine the order of acquisition of inflectional morphemes in these languages (Viana et al., 2017).

A major source of information on children’s morphological development is longitudinal corpus studies based on transcribed recordings of single or several children and their caregivers over months or years. Starting with Brown’s 1973 seminal work, this method is at the heart of current psycholinguistic investigation of morphological development. Such corpora are maintained in the open data-sharing resource project TALKBANK by Brian MacWhinney at Carnegie Mellon University. This system contains recorded, transcribed, and annotated spoken (and written) corpora in 34 languages, a large part of which is the children’s language bank CHILDES with tools for data elicitation, transcription, coding, and analysis of speech produced by children and their caregivers (Bernstein Ratner & MacWhinney, 2018; Davis, Lavie, MacWhinney, & Wintner, 2010; MacWhinney, 2008; MacWhinney & Snow, 1990). In recent years, dense recordings (several times a week) of dyadic parent-child conversations conducted over several years have provided rich, reliable, and interesting data on morphological acquisition, for example, Theakston and Lieven (2004) for English, Ashkenazi (2015); Ashkenazi, Ravid, and Gillis (2016) for Hebrew, and the Vienna-based multilanguage group researching early morphological development headed by Wolfgang U. Dressler (Xanthos et al., 2011). In recent years, the use of cross-sectional peer-talk corpora of children conversing with other children has also been recognized and used as an important source of information on children’s linguistic development (Veneziano, 2018). The current size and diversity of corpora recording child language and child-directed speech has made them an excellent source for studying how children learn their morphological systems in naturalistic settings, which can provide items for further, experimental investigations.

Beyond diary and corpus studies and parental reports, structured experimental studies are universally used to gain knowledge about children’s morphological knowledge in acquisition (see a review in Ambridge & Rowland, 2013). Experiments provide controlled settings where children’s knowledge of forms and functions can be tested in tasks of imitation, judgment, priming, comprehension, or production. The structured nature of experiments makes it possible to control the age and background of participants, to design specific conditions, and target items and categories that may not occur in all of their various forms in spontaneous speech, which is lexically sparse. For example, a study of gender agreement in Czech by Smolík and Bláhová (2019) created a specific syntactic environment to examine the anticipatory effects of gender-marking morphemes coming before the head noun; and the study of verbal passives, a structure that is rarely used in Hebrew, by Ravid and Vered (2017), included all three passive patterns in the language in both past and future tenses.

Experimentation can be designed to highlight various aspects of morphological knowledge. The use of nonce (made-up) words such as English-like blicked [blikt] is used to find out about children’s generalization abilities across a category, controlling for the effects of memory or of familiar vocabulary (Dąbrowska & Szczerbinski, 2006). Cross-sectional experiments can obtain information from a wide range of age groups to trace the learning path of a category from childhood to adulthood (Levie, Ben Zvi, & Ravid, 2017). Responses obtained by experimental methods can be analyzed across graded scales that provide detailed information about children’s developing morphological skills (Kjarbak & Basboll, 2016; Ravid & Malenky, 2001). And demands of different difficulty can be made in comprehension and production tasks to see their effects on children’s responses (Beyer & Hudson Kam, 2009; Gonzalez-Gomez, Hsin, Barrière, Nazzi, & Legendre, 2017).

Finally, computational modeling has increasingly played a role in child language acquisition as a methodology for studying morphological learning (Elman, 2005; McLelland & Patterson, 2002). Such models take natural language corpora as the data on which modeling is done (MacWhinney, 2010; Ramscar & Glitcho, 2007). Plunkett and Marchman (1993) showed how a neural network was trained on English past-tense forms, showing a gradual path of learning verbs, reorganizing from single-verb schemas to systematicity, just like children do in natural development.

4. Factors in Morphological Acquisition

Describing morphological acquisition can be likened to the proverbial attempt of different people to describe an elephant based on feeling its different parts. Real language is not easy to capture. The current review is based on research providing converging evidence from literature based on all of the different research paradigms described in the previous section so as to—ideally—capture a current picture of the elephant. Three critical factors platform the acquisition of morphology: input patterns in the ambient language, language typology, and development. The review of the roles of these three factors constitutes the bulk of this article.

4.1 Input Patterns in the Ambient Language

A major source of information on early child grammar is the linguistic input, or Child-Directed Speech (CDS) (Behrens, 2006; Hoff-Ginsberg, 1985; Maslen, Theakston, Lieven, & Tomasello, 2004). In general, speakers extract the properties typical of their native tongue from the surrounding ambient language. The distributional properties of CDS make it in many ways much more accessible to children than ADS (Adult-Directed Speech) and other forms of child-oriented language, like that of books (Cameron-Faulkner & Noble, 2013; Kern, Gayraud, & Chenu, 2014). Adult input makes various contributions to input to morphological learning. Beyond the prosodic fine-tuning typical of IDS (Infant-Directed Speech) (Snow, 1995), CDS involves clearer, slower speech than ADS. It is also more regular (Szagun, 2011), grammatically simpler, and less diverse, with fewer disfluencies and shorter and more grammatical utterances. CDS vocabulary typically consists of highly frequent, concrete words, carrying predictable, salient, child-oriented information (Fernald, Marchman, & Weisleder, 2013; McCauley & Christiansen, 2019). Even in languages with rich morphological systems, CDS is morphologically sparse, containing only a fraction of the possible alternations in morphological paradigms. The morphological contrasts that are prevalent in CDS and first marked in CS carry discriminative information that is highly interpretable from the surrounding circumstances, like plural marking, which first occurs on pluralia tantum nouns like, for example, stars, teeth (Ravid et al., 2008), gender and number marking on imperative and present-tense verbs, temporality markers such as the English -ing (Brown, 1973), or verb markings expressing basic transitivity relations (Berman, 1993; Levie et al., 2019; Ravid et al., 2016a).

CDS thus acts as a filter through which the most frequent and meaningful contrasts emerge. CDS often highlights morphological markers by pervasive use of diminutives (Dressler, Lettner, & Korecky-Kröll, 2012; Ravid, 1998; Ševa et al., 2007). Moreover, words and inflections are presented to children in a repeated, resonating manner, accompanied by elaborations, questions, and commentaries (Clark & de Marneffe, 2012; Lustigman & Clark, 2019; Rojas-Nieto, 2014). This enables children to extract transparent patterns that consistently reflect grammatical systematicity: in Hebrew, toddlers have been shown to rely on stable, frequently occurring inflectional verb affixes in maternal input to gain salient information on the opaque, irregular verb stems children often encounter (Ashkenazi, Ravid, & Gillis, 2016). The literature shows that children detect patterns in the speech they hear and form generalizations by using sociocognitive abilities of intention reading coupled with statistical learning and consequent schematization (Saffran, 2003; Tomasello, 2003). Abstract categories gradually emerge out of the specific items children have learned, based on the distributional properties of the input (Kilani-Schoch, Balciunienė, Korecky-Kröll, Laaha, & Dressler, 2009; Lieven, 2010; Lieven, Behrens, Spears, & Tomasello, 2003). This impact of frequency in CDS by caregivers on children’s output is apparent in corresponding token frequencies in child language (though with a lesser degree of productivity)—see Ashkenazi (2015) for Hebrew, Dressler et al. (2012) for Austrian German; and Krajewski, Lieven, and Theakston (2012) for Russian. And importantly, input differences also explain differences in patterns of acquisition among children. For example, Hadley, Rispoli, Fitzgerald, and Bahnsen (2011) show that children who receive more informative input have a faster rate of morphosyntactic development.

4.1.1 Frequency

Researchers agree that frequency is a fundamental property of the input that children receive, and that it affects morphological learning (Warlaumont & Jarmulowicz, 2012). In a review article, Ambridge, Kidd, Rowland, and Theakston (2015, p. 239) argue that “frequency effects are ubiquitous in every domain of child language acquisition” so that “any apparent null finding simply reflects a failure to conceptualize frequency appropriately, to find a sufficiently sensitive dependent measure, or to hold constant other relevant factors.” These effects have been recorded across all languages investigated in children’s acquisition—see, for example, a review in Demuth (2019), covering several typologically different Bantu, Romance, and Germanic languages, where the relative frequency of the morphological form was shown to be one of the factors that predicted children’s comprehension and production of that form. Frequency effects pervade the morphological acquisition literature. To take a few examples: for Finnish, Rasanen, Ambridge, and Pine (2014) found that error rate in verb inflection was related to token frequency of forms and person/number contexts. For Arabic, Albirini (2015) found that older children tended to use plural forms based on frequency distributions in the adult language. Lapidus Shin (2016) shows that frequent patterns of variation are easier to learn in Mexican Spanish. And for Austrian German, Korecky-Kröll and Dressler (2015a) find that children prefer overgeneralizations of the most frequent forms of inflected attributive adjectives in their mothers’ speech. Note, however, that frequency is not the only determining factor in morphological learning, and that its role changes with development (Goodman, Dale, & Li, 2008), interacting with a variety of linguistic, cognitive and contextual factors (Ambridge, Kidd, Rowland, & Theakston, 2015).

Frequency has different meanings regarding the different facets of morphology. In its simplest form, it refers to the token frequency of a word, a stem, or a root—that is, how often each of these occurs in the data. The notion of register has been applied to characterize the relative frequency of lexical items in more or less restricted communicative environments (Ravid & Berman, 2009; Ravid et al., 2016b). But token frequency can also apply to affixes, and since these attach to words, stems, and roots, both stem and affix frequencies must combine and interplay, as in the example of a very frequent word such as Hebrew ax ‘brother’ taking the rare optional third-person possessive suffix –av to yield the high-register possessive form exav ‘his brothers’. Marquis and Shi (2012) show the combined effect of frequency with other factors for early morphological learning, claiming that the encoding of bound functional morphemes in infant perception is determined by the frequent occurrence of the morphemes with highly variable roots. Ashkenazi et al. (2016) show the same distributions in Hebrew.

A second facet of frequency in morphology is type frequency, which refers to the number of members in or the size of a category. The higher the type frequency of a category, the more established and coherent it is, making it easier to extract generalizations across its members (Marchman & Bates, 1994). Large category size is related but not identical to the notion of affix productivity in a morphological system, measured by the number of types it applies to (Bauer, 2011; Korecky-Kröll & Dressler, 2009). Productive categories are learned earlier and faster in child acquisition (see, for example, Albirini, 2015, for Arabic, and Kjarbak & Basboll, 2016, for Danish). The advantage of categories with high-type frequency in learning morphological systematicity is apparent, for example, in the acquisition of the Arabic plural, where the regular, productive “sound” feminine and the irregular, non-productive “broken” plural categories have similar, early developmental trajectories; whereas the regular, but non-productive masculine expressing semantic agents is a challenge until later ages (Aljenaie, Abdalla, & Farghal, 2010; Ravid & Farah, 1999; Ravid & Hayek, 2003). Both type and token frequency have been shown to be immensely important in children’s developing morphological systems (Nicoladis, Palmer, & Marentette, 2007; Ragnarsdóttir, Simonsen, & Plunkett, 1999), as type frequency helps construct and entrenches regular categories while token frequency promotes the learning of specific, often irregular forms (Theakston & Lieven, 2004).

Yet another facet of frequency is the notion of “frequent frames,” sequences of words that repeatedly co-occur in discourse (Arnon & Snider, 2010). Recent studies indicate that morphological structure and meaning are packaged and presented, especially to young children, in frequently occurring morphosyntactic contexts of surrounding words termed “frequent frames” (Matsuo, Kita, Shinya, Wood, & Naigles, 2012; Mintz, 2003; Moran et al., 2018). Such frames provide young children with semantic-syntactic information from the immediate context, serving to highlight the boundaries and functions of categories and word-internal morphology (St. Clair, Monaghan, & Christiansen, 2010; Wilson, 2003; Yuan, Fisher, & Snedeker, 2012). Repeated exposures to frequent frames is one way to extract morphological generalization as an emergent property (Bannard & Lieven, 2012).

4.1.2 Learning in Interaction

Input does not serve merely as a source of quantitative data for children to process; rather, it provides the communicative context where children pay attention to morphological markers as meaningful cues to caregivers’ intentions in interactive sociopragmatic settings of joint attention (Tomasello, 2003). Children pay attention to discourse pragmatic cues, including adults’ (and peers’) reactions, questions, commentaries, requests for clarification, construals of homophonous forms, and recasts, based on the “common ground” they share (Clark, 2015; Clark & de Marneffe, 2012; Uno, 2016). Moreover, there is mounting evidence that children require, receive, and make use of efficacious positive and negative, direct and indirect feedback on their language productions over a long period of time (Chouinard & Clark, 2003; Clark, 2010; Moerk, 1991). These interactions help children learn morphological markers of number, gender, person, case, temporality, and mood (Ibbotson, Lieven, & Tomasello, 2014), ontological categories, and lexical class distinctions (Clark & Berman, 1984; Clark & Hecht, 1982; Ravid, 2004) as critical cues to meaning and function. Interactions moreover guide children in understanding human actions and motivations underlying the events and situations in which they participate.

4.2 Target-Language Typology

Languages differ in the amount of information they package inside words. Hebrew mavreg and its counterpart English screwdriver are both morphologically complex words, but they are constructed very differently. The Hebrew mavreg is composed of the consonantal root b-r-g and the pattern maCCeC (where C stands for root consonants) commonly used to denote instrument nouns (cf. maxshev ‘computer,’ mastem ‘valve’); and screwdriver is a compound noun ending with the agentive/instrumental suffixt -er. But the English noun screw is morphologically simplex, whereas its counterpart Hebrew bóreg is also composed of a root and pattern structure, related to mavreg ‘screwdriver’ via its shared root b-r-g, and to other nouns such as tófes ‘form, file’ or shóresh ‘root’ via the shared pattern CóCeC. This demonstrates a key typological difference between English, as a relatively analytic language that relies largely on lexical and syntactic means of expression, and Hebrew, as a synthetic/fusional language, where many grammatical and lexical notions are encoded by word-internal devices, both linear and non-linear in structure (Berman, 1978, 1982). Other language types are Turkish, an example of a synthetic/agglutinating language with sequences of transparent linearly suffixed morphemes, while Basque is a polysynthetic language with a great density of morphemes within a single word. These differences reflect the ratio of morphemes per word in a given type of language in general and the rates of acquisition in particular.

Very early on, children are peculiarly attuned to the typological features of their mother tongue (Berman, 1986). Native input patterns affect the order of emergence of morphemes and the nature of errors children produce: in comparing Italian with Hungarian, a more heavily inflected language, Gervain and Erra (2012) showed that the morphosyntactic properties of the language influenced which statistical measure of segmentation had a better performance (Gabor & Lukacs, 2012). For Korean and English, Onnis and Thiessen (2013) showed that different probabilistic preferences in learning that were unique to the structure of each language increased over time. Typological differences appear to regulate not only rate of acquisition but also children’s error patterns. For example, where young children tend to use bare, non-finite forms in Germanic languages, they tend to produce infinitives as the least informative form in the Hebrew verb inflection paradigm (Lustigman, 2012), and they tend to use less marked pronominal agreement forms in Italian, a language with morphological verb classes (Pizzuto & Caselli, 1992). In the same way, Bangla-speaking children (Bangla is an Indo-Aryan language spoken in South Asia) were shown to replace tense/aspect markers by less marked, more frequent ones, rather than omitting them completely (Sultana, Stokes, Klee, & Fletcher, 2016). And in Basque and Spanish, languages with rich inflection, very few root infinitives were produced by young learners—and the rate of these omission errors closely resembled that of adult speakers, which was higher in Spanish than in Basque (Austin, 2010).

When their native tongue has rich morphological patterning, as in Icelandic, Russian, or Hebrew, children’s attention is focused on the morphological arena from early on (Ravid, 1995; Thordardottir & Weismer, 1998). In Italian, children gain command of inflectional morphology before they gain syntactic command (Caprin & Guasti, 2009). In a comparative study of nine typologically different languages, Xanthos et al. (2011) showed that the morphological richness of inflectional systems in CDS had a strong positive correlation with the speed of morphological development in child speech (CS), using the measure of MSP (mean size of paradigm) (Gillis & Xanthos, 2010). These results reflect the “typological impact”—children’s early sensitivity to the typological properties of their language, which leads them to pay attention to the ways pertinent information is encoded in grammatical structures (Berman, 1986; Choi & Bowerman, 1991; Slobin, 1996). For example, words in Inuit languages may contain up to 10 morphemes, with children productively expressing complex morphological structures such as causatives, passives and noun incorporations as early as age two (Allen, 2017) at a fast pace that is very different from that of English (Messenger, Branigan, & Mclean, 2012).

4.3 Development: From Morphological Emergence to Productivity

Gaining productivity in morphology means being able to make language-appropriate, automatic use of morphological structures and meanings regardless of specific linguistic or communicative context. In undertaking to describe how children gain productive command of their respective morphologies in different languages, the problem again arises of describing the proverbial elephant by feeling its different parts, or conflating the evidence from many disparate sources. The “elephant” is composed not only of the many and different languages, language families, and typologies where morphological systems serve human expression. It also involves the different ways acquisition (in the case in point of morphology) is assessed: by following growth patterns in individual children or by testing cohorts of children; by examining production, comprehension, or other methods of assessment such as judgment or repetition; or by analyzing frequency distributions in corpora. All these factors, along with researchers’ assumptions about morphology and what constitutes evidence of acquisition, affect the way the “elephant,” the course of morphological acquisition, is viewed. The review that follows does not claim to take into account every piece of the large body of evidence accrued by the research literature and all points of view, but it does aim to provide some idea of how morphology emerges and consolidates in children’s first-language acquisition. Compelling evidence shows that morphological acquisition follows a shared path in development from several perspectives. One such generalization is that across languages, children’s productions evolve from simplex to more complex, with morphology being a domain of much change in this respect. Another is that morphology, like syntax, emerges as non-productive and becomes productive. Yet another is that semantic or conceptual complexity increases together with the growth of structural complexity. Further, emergence and consolidation of the central morphological systems typically take place between the ages of two and six years, while mature command of all systems and subsystems can take up to 10 more years, and is mediated by the consolidation of literacy skills. Finally, morphological learning in both inflection and derivation is always interwoven with lexical growth in the sense of gaining more, and more diverse, words, as well as deepening the senses each word carries. This is the elephant. Beyond these similarities, morphological acquisition in every language takes a distinct route, which is mediated by language typology, morphological complexity and systematicity, specific lexical class, and frequency factors.

That children undergo a temporal progression from single words to word structure and word combinations is a fact. One way of approaching this process is by comparing children’s morphological performance to that of adults to determine when and how children attain adult-like abilities (Blom, Polišenská, & Weerman, 2006; Clahsen & Fleischhauer, 2014). In the following sections, development itself is treated as a central mechanism that drives morphological acquisition from emergence to productivity (Samuelson, 2009). The role of development as an explanatory mechanism is viewed from three perspectives. First, development is viewed as a filtering device that enables learners to break into the morphological system (“starting small”); second, development is seen as providing the stretch of time necessary for emergence and consolidation of morphology (“growing paradigms”); and finally, development is seen as hosting the cognitive changes that usher in mature systems (“gaining control”).

4.3.1 “Starting Small”: Morphological Emergence

Development is a critical driving force explaining initial morphological learning. Morphological paradigms in many languages are complex, presenting a daunting task for even adult language learners. How do native-language learners, with limited memory and attention resources, break into such systems? Innate, abstract knowledge and universal maturational constraints have been invoked (Chomsky, 1988) to explain the discrepancy between complex, rich, and automatic morpholexical usage in adults, on the one hand, and children’s limited cognitive abilities and the purported absence of negative evidence in language learning, on the other. However, this view assumes morpholexical development takes place along a straight line, whereas other views show that dynamic non-monotonic learning in naturally noisy, constantly changing environments is key for morpholexical development (Elman, 2003). The usage-based model of “starting small” by Elman (1993) views children as starting out with limited cognitive resources that allow for data to be presented only incrementally while, in terms of input, they are first exposed to only a limited number of frequent, salient, contrasting, low entropy (= high predictability) examples of a language category in supporting pragmatic environment (and see, too, Ackerman & Malouf, 2013; Clark, 1987; Ellis & Ogden, 2015). For example, consider two very early emerging morphological markers that fulfill these requirements: -ing suffixed durative verbs in English, or imperative feminine singular -i suffixed verbs in Hebrew (kax/kxi ‘take/take, Fm’). According to Elman, repeated exposure to such salient structures is highly effective early on in development, as learning networks are most sensitive during the early period of learning, enabling the break into the system. At the same time, limited cognitive capacity shields the infant from stimuli which may either be irrelevant or require prior learning in order to be interpreted, acting as a filter on the input to focus learning on just a small, highly meaningful subset of the data. Thus in fact, nonlinear change can emerge from a set of basic, simplex principles that combine to form a developmental cascade (Samuelson, 2009).

4.3.1.1 Lexical Class

An important factor in early morphological acquisition is lexical/syntactic class. This is because morphological operations require information relating to the semantic and structural features of nouns, adjectives, and verbs (Kemmerer, 2014). When approaching the initial acquisition of morphology, each part of speech poses different challenges to learners in identification of grammatical class and in morphological production in language-specific context, for example, in the ratios of regular to irregular items in English (Theakston & Lieven, 2004). The cross-linguistic investigation of Onnis and Christiansen (2008) into segmentation in infancy showed that across typologically diverse languages, infants make use of low-level information at the beginning and endings of words (phonemes and syllables, depending on language type) to eventually identify lexical categories. In many cases, these sites at the edges of words may coincide with grammatical morphemes such as English -ing (Veneziano & Clark, 2016). In a cross-linguistic study of seven languages, Moran et al. (2018) showed that frequent frames involving the morpheme level made such frames very accurate as predictors of noun and verb stems. Such morphemic frames were found to be better predictors of grammatical class in morphology-rich languages with free word orders than in morphology-sparse languages (Mintz, 2003). To give a specific example, non-linear patterns in Hebrew have distinct nominal and verbal forms, with class-specific prefixes and suffixes, as well as vowel-internal templates (Ravid, in press) and differential prosodic behavior in CDS (Conwell, 2017; Segall, Nir-Sagiv, Kishon-Rabin, & Ravid, 2008). These characteristics were shown as critical in toddlers’ initial break into the system (Ashkenazi et al., 2016). Taken together, these studies show that the input contains information that makes it possible for children to early on identify those word classes they will need to inflect and derive.

4.3.1.2 Diminutive Mediation: The Beginning of Morphological Operations

Toward the end of the second year of life, toddlers often produce filler syllables that eventually evolve into the first morphemes (Veneziano & Sinclair, 2000). Acquisition of morphology can be said to start around 22 months (toward the end of the second year), when production vocabulary reaches a critical mass of several hundred words. One strategy used in many languages in the transition into morphology is the use of diminutives expressing hypocoristic, endearment sense in CDS addressed to infants and young children, especially in languages with productive diminutive devices (Savickiene & Dressler, 2007). A series of studies in Finnish, Dutch, Russian, Serbian, and Lithuanian showed that the use of diminutives (e.g., Lithuanian masculine -ukas and feminine -uke) had a facilitative effect on children’s acquisition of gender and case morphology: Children hook onto diminutive forms as clusters of morphophonologically salient and homogeneous words, which regularize metric stress (Kempe et al., 2009; Savickiene, et al., 2009; Ševa et al., 2007). In Hebrew, juvenile -i diminutive suffixes attach to both feminine and masculine nominals, highlighting word endings while leaving word structure and stress completely unchanged, unlike any other morphological suffix (Ravid, 1998). This non-prototypical nature of diminutive morphology was inherent in all of the systems described in Dressler and Korecky-Kröll (2015).

4.3.1.3 Initial Morphological Markings

The first morphological markers tend to be the most frequent, morphophonological salient, communicatively meaningful items and categories in the language (though not necessarily all of these features together). They are typically in the inflectional domain, where semantics is mostly predictable and transparent, and markers have low-type and high-token frequencies. Across languages, two-year-olds start by producing their first inflected words construing events as having telic, perfective, or durative/imperfective character, and designating individuated entities by number/gender/person markers. Examples include present progressive in Bangla (Sultana et al., 2016); perfective ba in Mandarin Chinese (Deng, Mai, & Yip, 2018); the plural English -s and durative -ing (Brown, 1973); present, imperative, past, and future verb forms in French (Trudeau & Sutton, 2011); plural and gender noun marking (Szagun et al., 2006), and regular, frequent participles in German (Szagun, 2011); Hebrew imperative verb feminine -i and nominal plural -im (Ashkenazi, 2015; Berman, 1985); third singular indicative in Greek (Christofidou & Stephany, 2003) and in Italian (Caprin & Guasti, 2009); the telic, perfective Japanese past-tense marker -ta; or the Turkish past tense -di and imperfective -iyor (Aksu-Koc, Terziyan, & Erguvanli Taylan, 2014). These initial, non-productive inflected forms are first highly restricted in meaning, attached only to those frequent words that are relevant and familiar to children. They appear at a time when most other words in children’s discourse are uninflected or unmarked and phonologically unstable.

This section has treated development as a filtering device used by learners to break into the morphological system (“starting small”). In the next section, development takes on the role of providing the time scale necessary for the emergence and consolidation of morphology (“growing paradigms”).

4.3.2 Growing Paradigms: Morphological Proliferation

A second facet of the notion of “development” is ample time to gain experience in word formation in a Zipfian world (Lignos & Yang, 2016). As mentioned in section 4.3.1, young children participate in discourse that is morphologically sparse, in the sense of type and token frequencies. Inflectional paradigms and derivational families in input to children and in their own speech are limited and small and occur in restricted communicative environments. For example, around age two, Hebrew-speaking children mostly hear and produce modal verbs, with little tense marking (Ravid et al., 2016a). Moreover, most of the verb tokens in their input and output up to age eight are in one highly frequent but non-productive verb pattern (Berman, 1993), and the majority of these verbs are singletons, i.e., do not share roots with other verbs in the corpus (Levie et al., 2019). In order to gain command of the full variety of forms and meanings, including rarer categories with fewer exemplars and categories that have indirect linkage with other categories, a learner needs time to grow their lexical inventories (Leonard, 2019; Swan, 2000; Trudeau & Sutton, 2011). Development is thus key in another sense. It provides the time—years, in many cases—for children to encounter a variety of words with different structures in different communicative settings often enough so as to be able to generalize across smaller, low-frequency, more specific categories, and to disperse ambiguities and subtle distinctions in usage, such as the -s suffix in English (Ambridge, 2013; Beyer, & Hudson Kam, 2009; Labrell et al., 2014). This is especially true in languages with very rich, often opaque morphologies that require many and diverse encounters to extract information out of various inflectional and derivational classes (Ben Zvi & Levie, 2016; Fhlannchadha & Hickey, 2017; Thordardottir, Weismer, & Evans, 2002; Vainio, Pajunen, & Häikiö, 2019).

The route to productive morphological use in preschool children is gradual and slow rather than abrupt, as attested by both naturalistic and experimental studies (Gathercole, Sebastián, & Soto, 1999). For example, the study by Zapf and Smith (2007) of English-speaking children’s learning of plural morphology from 17 to 28 months showed that young children’s performance on generalizing the regular plural did not resemble rule-like knowledge applicable across the board but was, rather, limited to a few novel nouns. A similar developmental pattern was found in the study by Aguado-Orea and Pine (2015) of the development of verb morphology in Spanish-speaking children. From the end of the second and across the third year of life, child language corpora tracing the linguistic development of preschool children show interrelated morphological, lexical and syntactic growth and elaboration (Parker & Brorson, 2005; Viana et al., 2017). With children’s vocabulary increasing across lexical and function categories and the stabilization of phonological forms (Demuth, 2018), small, restricted morphological alternations emerge in tandem with the advent of syntax, heralded by the appearance of function words (articles, pronouns, prepositions, conjunctions) and grammatical word order (Berman, 1986; Dressler, 2011; Le Normand, 2019). Morphological productivity emerges when alternations become more numerous, and increasing numbers of inflected words of various types occur in corpora, so that MSP increases. These changes mirror the increasing complexity in the ambient language, although children’s morphological productivity always lags behind that of the adult input (Aguado-Orea & Pine, 2015; Ashkenazi, 2015; Krajewski et al., 2012). This process is affected by the type of language being acquired. It takes several years even in languages with sparser morphologies for the central morphological systems to proliferate and diversify. This is because children need to be exposed to an adequate number of examples of the less regular or the smaller classes and of items with a smaller token frequency to construe the structural and semantic relationships between them. During this period of intense learning in the preschool years, children’s construction of morphological systematicity continues to reflect the interplay between the input characteristics and cognitive abilities and strategies. For example, English third-person singular -s is not only less frequent in the speech of caregivers than the plural noun -s (Warlaumont & Jarmulowicz, 2012), the very fact that it is a portmanteau morph that encodes tense, aspect, and number, as well as possessive case, makes it less readily accessible in children’s comprehension up to age seven (Beyer & Hudson Kam, 2009).

But in languages with richer, more complex, fusional morphological systems, while morphological learning starts early on, this process takes longer. For example, in Norwegian and Icelandic, the path to knowledge of all classes of past tense takes up to age eight years (Ragnarsdóttir, Simonsen, & Plunkett, 1999). In Austrian German, on the one hand, and in Palestinian Arabic, on the other, learning all of the noun plural classes is still under way at age six years (Laaha et al., 2006; Ravid & Farah, 1999; Ravid & Hayek, 2003). And in Hebrew, irregular agreement marking on adjectives, deriving from the interplay of type frequency, gender, stem change and plural suffix type on nouns still challenges 12–13-year-old pre-adolescents (Schiff, Levy Shimon, & Ravid, 2011; Ravid & Schiff, 2012). This description is by no means universal. The situation is rather different in agglutinating languages, where a variety of inflectional and derivational suffixes are already productive in the speech of two-year-olds. In Bantu languages, passive forms are productive by age three (Alcock, Rimba, & Newton, 2011; Demuth, Moloi, & Machobane, 2010). In Finnish, children can produce present tense, past tense, and several frequent case markers before 2;6 (Lyytinen & Lyytinen, 2004). In Hungarian, longitudinal case studies showed that 29 different inflectional markers expressing tense, agreement plurality, and case were already produced by age 2;3 (MacWhinney, 1976). And in Turkish, where inflectional morphology is regular and transparent, productive use of inflections is in place as early as age two years, with multiple markings on the same form (Aksu-Koc, 2010; Aksu-Koç & Ketrez, 2003; Ketrez & Aksu-Koç, 2009). Finally, in Sesotho, a Bantu language, children are already able to carry out nominal agreement between two and three years old (Demuth & Weschler, 2012).

Polysynthetic languages with densely rich morphologies contrast hugely with the developmental pace of less complex systems. Fortescue (1984–1985) recorded dyadic conversations of a two-year-old boy in Greenlandic, a language with over 400 derivational affixes and 318 inflectional endings. At the time when English-speaking children take their first steps into inflection (Brown, 1973), during a half-hour session this child used mostly morphophonologically correct derivational affixes (24) and grammatical inflections (40), attached to several stems. In her studies of Inuktitut in Arctic Canada, Shanley Allen found that at the two-morpheme stage, Inuit children are already productively producing many derivational and inflectional morphemes (Allen, 2017). In sum, the facilitative effect of languages with rich and/or transparent, high-frequency morphological systems promotes very early productivity in inflectional and derivational morphology.

This concludes the section of development in the sense of time allowed for the proliferation and growth of morphology. The final section on the notion of development as the factor driving morphological acquisition examines its role in the period of later language development, where cognitive change drives the consolidation of spoken and written morphology.

4.3.3 Taking Control: The Consolidation of Morphology During the School Years

Experiments by Elman (1993) in learning networks indicated that the network abilities of data processing gradually improved, with more complex but less representative subcategories and items joining in to construct categories over time. With development, networks were shown to be less sensitive to small differences in the input and more likely to behave categorically. This section introduces the third and last perspective on the contribution of development to learning morphology. Beyond acting as a filtering device for learners to break into the system, and beyond allowing them the time to experience the system and acquire its parts, development has to do with the changing character of the learning system available to young learners with time. Whereas infants approach information in discourse using cognitive tools of pattern detection, segmentation, and generalization (Ota & Skarabela, 2018), older learners face complexity in the data but are better able to process it. Being able to extract information from larger and more diverse samples of the data and gaining command of less prominent categories and items comes with developing cognitive capacities of attention, memory, and processing in later language development (Berman, 2005; Nippold, 2016). Karmiloff-Smith (1992) proposed a model of development from implicit to explicit metalinguistic knowledge reflecting patterns of reorganization in the maturing brain, whereby knowledge becomes more integrated, denser, and more readily accessible (Tibi, Tock, & Kirby, 2019). Along similar lines, Ramscar and Glitcho (2007) show that morphosyntactic acquisition changes its character from unsupervised learning in early childhood to more agentive, self-monitored “supervised” learning typical of older childhood and adolescence. An important part of these developments is gaining command of executive control functions in adolescence (Crone, 2009), which enables individuals to monitor, control, switch, and coordinate actions and thoughts. Thus, development increases the complexity of the human learning architecture, allowing learners to filter their attention to less frequent and prominent features in linguistic systems (Ramscar et al., 2018). To accomplish this, the learning system itself changes with time and experience to adapt to the changing structure of the linguistic input (Onnis & Thiessen, 2013).

5. Derivational Acquisition

Derivation is the semiproductive, less semantically predictable and transparent, non-obligatorily applicable component of morphology expressing lexical notions and relations, with high-type frequency and restricted token frequency (Dressler, 1989). Derivational morphology organizes the lexicon and enables the formation of new lexical items. As such, derivational categories are not often among the first to be expressed by morphological markers in very early child language (Slobin, 1985–1995). For example, Diamanti et al. (2018) showed in a study of Greek children ages four to seven years that production of derivational morphemes was consistently more difficult than production of inflectional morphemes. The pace of acquisition of derivational morphology depends on the degree of morphological richness in the ambient language, starting earlier on where derivational morphemes are frequent and meaningful to lexical expression. Thus, Schipke and Kauschke (2011) showed for the acquisition of German that word formation markers were already evident by age 1;9 and showed rapid development concurrently with lexical attainment. And Ashkenazi, Gillis, and Ravid (2019) demonstrate that the acquisition of the Hebrew derivational verb system starts as early as age two years, growing side by side with inflectional complexity. Moreover, there are indications that derivational productivity soon follows in the steps of inflection, even in languages with sparser morphology than German or Hebrew, when children seek to express notions that are not within their lexical inventories, as attested by their spontaneous coinages (Becker, 1994; Clark, 1995, 2014). And studies indicate that the same factors that operate in inflectional learning apply in derivational development—namely, the different facets of development in interaction with input patterns, and language typology, with specific lexical category. To sum up this section, as derivational morphology necessitates ample experience with different lexical items to gain systematicity and productivity, its development is generally associated with the lexicons of older children, especially during the school years.

An example from English illustrates the interplay of language factors in the acquisition of derivational morphology. In a judgment study of verbs prefixed by -un (untie, *unsqueeze), Ambridge (2013) showed a complex developmental route in children ages five to ten years, compared with adults. This process was governed by verb semantics and frequency effects of entrenchment and pre-emption. A study by Argus and Kazakovskaya (2018) compared derivational development in Russian and Estonian, illustrating the effects of language typology: While both are morphologically rich languages, Russian has more regular, productive, and frequent derivational systems, whereas in Estonian derivation is more opaque. The analysis of children’s productions in development showed that they mirrored the patterns typical of each language, respectively. The impact of language typology regarding specific morphological devices is apparent in the highly researched domain of the root construct in Hebrew. Semitic roots are non-continuous, non-pronounceable sublexical entities (e.g., g-d-l ‘grow’). Nonetheless, by their third year of life, Hebrew-speaking children show a marked preference for root-based formation in nouns, adjectives, and most especially in verbs (Berman, 1982, 1985, 1993, 1999; Clark & Berman, 1984; Ravid, 1995, 2003, 2004; Ravid et al., 2016a). This preference mirrors the central role of roots in the Hebrew lexicon (Ravid, in press).

Use of conversion (or zero-derivation) as one of the first devices in children’s coinages is a final example of how language patterns dictate lexical innovation patterns in young speakers. Conversion changes a lexical category without making any overt structural changes in the word (e.g., document, N to document, V). As a simple and frequent device, it can be expected to appear early on in children’s productions. In English, this device is widespread in the conversion of nouns into verbs (Clark & Clark, 1979). Relatedly, Clark (1993) reports conversion examples such as to sand (in the sense of grinding into powder) or to rug (vacuum the rug) in English-speaking children aged two to three. But in Hebrew, N to V conversion is impossible, given the strict root-and-pattern structure of verbs. Instead, V to N conversion is a highly prominent device in Hebrew (Ravid et al., 2016b), as in moxer ‘sells, V / vendor, N.’ Concomitantly, this is one of the first nominal derivational devices used by children (Ben Zvi & Levie, 2016; Ravid, 1995).

5.1 Derivational Morphology in Later Language Development

The acquisition of derivational morphology has been the topic of far less research than the domain of inflection, as reflected in this article. This may be the result of a research focus on English, where inflection is far more pervasive and productive than derivation. It may also be due to the fact that derivation is perceived as part of vocabulary attainment, and therefore pertaining to educational or literacy domains rather than to basic issues in first-language acquisition. Nonetheless, language skills, of which derivational morphology constitutes a major part, continue to develop across the school years until young adulthood and beyond (Berman, 2007; Nippold, 2016). Derivational categories develop from concrete to abstract expression. In Hebrew, a fusional language with many derivational devices, preschoolers first mark agent and instrument nouns in spontaneous and elicited productions (Clark & Berman, 1984), followed by place and collective morphology during the school years (Ravid, 2004; Ravid, Avivi-Ben Zvi, & Levie, 1999). Maturing cognitive and interpersonal skills and the consolidation of linguistic literacy usher in abstract reasoning and increasing analytic capability (Crone, 2009; Fortman, 2003; Lee et al., 2018; Ravid & Tolchinsky, 2002), which find expression in complex words typical of written, academic language (Anglin, 1993; Ben Zvi & Levie, 2016). Gaining comprehension and usage of complex, abstract words such as derived nominals (demonstration, complexity, childhood) (Ravid & Avidor, 1998) or derived adjectives (administrative, intentional) (Cutillas & Tolchinsky, 2017; Ravid & Levie, 2010) is a long developmental process (Dawson, Rastle, & Ricketts, 2018; Ravid & Berman, 2009; Vainio, Pajunen, & Häikiö (2018)) that relies heavily on active literate experience (Berman, Nayditz, & Ravid, 2011; Dąbrowska, 2018; Larsen & Nippold, 2007; Nippold & Sun, 2008).

5.2 Writing Morphology

In many languages, morphemes are consistently reflected in orthographic systems as in the case of English suffixes -tion or -ive. This necessitates the incorporation of morpho-orthographic knowledge into the route of inflectional and derivational acquisition in its broadest sense, the construction of a multimodal lexicon (Deacon & Bryant, 2005; Ravid, 2012; Turnbull, Deacon, & Kay-Raining Bird, 2011). In comprehension, Perry, Ziegler, and Coltheart (2002) showed that English-speaking adults take into account morphological chunks in assessing “wordlikeness” in spelling judgments. Recently, D’alessio, Jaichenco, and Wilson (2018) showed that reading fluency in languages with transparent orthographies such as Italian and Spanish benefits from morphological abilities. And from the production perspective, Treiman and Kessler (2005) showed that young English spellers take into consideration clear morpho-orthography cues, such as the fact that derivational couplets of stem adjective (or verb)/derived abstract nominal such as divine/divinity or serene/serenity retain the same vowel letter, despite the phonological difference between a diphthong and a short vowel.

In his review of the role of morphology in reading and writing, Sandra (2018) provides rich cross-linguistic evidence that morphological structure plays a considerable role in both spelling and reading at different levels of processing and in interaction with other linguistic domains. He concludes that “Morphology leaves its stamp on spelling and reading from the beginning of a child’s literacy skills until the stage when language users have become expert spellers and readers” (p. 497). Like all areas of morphological acquisition, different levels of transparency and frequency of complex written words affect their processing (Deacon, Whalen, & Kirby, 2011). And in written morphology too, language typology plays a crucial part in children’s developing abilities, as demonstrated in the Dutch-Hebrew spelling morphology study by Gillis and Ravid (2006): the Hebrew orthography reflects the major morphological divide of roots and affixes in a way that facilitates the acquisition of spelling (Ravid & Bar-On, 2005). Accordingly, knowledge of morphology was shown to promote the acquisition of writing from kindergarten to first grade (Levin, Ravid, & Rappaport, 2001).

While statistical properties of written language affect the acquisition of written morphology, it often requires supervision and direct instruction that involve meta-linguistic thinking about the representation of morphemes in writing. For example, in French, where spelling brings to consciousness grammatical information that is not available in spoken language, children in third and fourth grades were able to use morphological information in spelling, especially in derived words (Casalis, Deacon, & Pacton, 2011; Duncan, Casalis, & Colé, 2009). The focus on literacy instruction not only requires morphological awareness—the ability to think explicitly about morphological structures and meanings—but also promotes it, resulting in intensified and rapid morphological and lexical learning in elementary school (Li, Cheng, & Wu, 2017; McBride-Chang et al., 2008; Pan et al., 2016; Ravid & Schiff, 2009).

The central role of morphology in language acquisition, and especially its importance in lexical learning, renders it vulnerable to adverse learning conditions that hinder morphological attainment. Morphological deficiencies have been found in a variety of conditions such as neonatal prematurity (Ketrez, 2018), cognitive impairment (Thomas & Karmiloff-Smith, 2003), developmental language, reading, and attention deficits (Bedore & Leonard, 2005; Rakhlin, Kornilov, & Grigorenko, 2014; Schiff et al., 2016), and the impact of poverty and disadvantaged social environment (Fernald, Marchman, & Weisleder, 2013; Levie, Ben Zvi, & Ravid, 2017; Ravid & Schiff, 2006, 2012). This topic, mentioned here only briefly, is of major importance in first-language development of morphology, with critical implications for brain development and consequent gaining command of linguistic literacy (Romeo et al., 2018).

6. Concluding Note: Morphological Learning

Morphological knowledge relates to word-internal structures and their meanings. In some languages, not much semantics is encoded in morphological forms. In others, there is almost nothing but morphology. Children are born learners. They can initially tackle any structure that encodes prevalent, consistent, distinctive, predictable, and meaningful information in their language. Thanks to cognitive abilities of attention, pattern detection, and generalization, mediated by interaction with caregivers and modulated by prior experience, children are eventually able to piece together complex structural, semantic, pragmatic, and distributional cues to achieve full, automatic command of morphology in their language. All routes to mature morphological knowledge in typically developing children share these properties; however, the length of the route, the pace of acquisition, and the final shape of morphological systems that emerge in first-language learners depend on the ambient language that they have experienced.

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