Introduction

Arabic is a Semitic language that is used as a first language by approximately 206 million people and as a second language by about 246 million speakers (Gordon, 2005). It is characterized by diglossia (Ferguson,1959), a linguistic situation in which two varieties of the same language have a functional distribution, with the spoken variety used in informal and intimate contexts and Modern Standard Arabic (MSA), the written variety, acquired through literacy and used in written and formal discourse. Each Arab state has its own dialectal variety while MSA is the official language of 20 Arab states. All Arabic speaking children first acquire the dialectal variety as their mother tongue and are only later introduced to MSA through literacy.

Key Research Questions

The questions raised by Arabic acquisition researchers aim to 1) study the stages of development of Arabic speaking children in phonology, syntax, morphology and semantics, 2) examine the effects of language typology, i.e. the specific characteristics associated with each language family on order of acquisition, and 3) inform the 'universal vs particular' discussion within generative research on language acquisition, which is based on the view that both universal innate linguistic predispositions and particular properties of each language are involved in the process of acquisition. Some studies also look at physiological and social factors that affect the order of acquisition of different aspects of language in both its oral and written forms. There seems to be no published work dealing with discourse or pragmatics acquisition to identify the developmental stages in learning how to use language appropriately in social interactions.

Recent research addresses specific acquisitional aspects in the dialect being studied, for example, Emirati (Ntelitheos & Idrissi, 2008), Jordanian (Amayreh, 2003; Amayreh & Dyson, 1998, 2000), Kuwaiti (Aljenaie, 2001), Palestinian (Ravid & Farah, 1999, 2001; Friedman & Costa, 2007), Moroccan (Badry, 1983, 2004) and Saudi (Al-Akeel, 1998; Moawad, 2006). Dialect acquisition has also been studied in children with specific language impairment (SLI) (Abdalla & Crago, 2008; Friedman & Costa, 2007; Salameh, Håkansson, & Nettelbladt, 2004). There is also a growing interest in studying bilingual development of Arab children in Europe, Lebanon and Palestinians in Israel (Altena & Appel, 1982; Gathercole, Moawad, & Thomas, 2008; Håkansson, Salameh, & Nettelbladt, 2003; Ravid & Farah, 1999; Ravid & Hayek, 2003; Zablit & Trudeau, 2008). Increasing research is being carried out on reading acquisition by Palestinian Arab children in Israel (Saiegh-Haddad, 2004, 2007) and elsewhere (Abu-Rabia, 1995), particularly in light of the diglossic character of Arabic.

Recent Research Results

Milestones in the Acquisition of Arabic Phonemes
Phonological acquisition studies reveal stages in the development of phonetic inventories of Arabic sounds that are similar to other language inventories with important particularities. At the prelinguistic stage (6-10 months), vocalic inventories include mid and back high and low vowels [ə, ε, e, u, ӕ, a] but not the high front vowel [i] (Omar, 1973). Consonantal inventories include stops (e.g., sounds that stop the airflow /p,b,t/), fricatives (e.g., blowing sounds /f, s/), nasals (e.g, /m, n/), and glides (e.g., /w/). Amayreh et al. (2000) report the production of fricatives [ћ,š] liquid [l] and the glottal stop [ʡ] both in initial and final syllable position by 14-24-month-old Jordanian children. The stages in phonological acquisition reported in Arabic reveal five stages in phonological development as illustrated in Table 1.

Table 1: Stages in the acquisition of Arabic consonants
Adapted from Omar (1973) and Amayreh and Dyson (2000)

	babbling	14-24ms	2-3:10yrs	4-6:4yrs	6:5-8yrs
Stops	b, p	b, d, t, ʡ	k, q, g		t, d
Fricatives/affricates	h	š, ʢ, ћ, h	f	s, χ, ð, γ, θ, ʤ, s	ð, z
Sonorants/liquids	m	m, n, l		r
Glides	w, y	w, y
Totals		13	+4	+8	+4 = 29

The earlier production of the glottal stop and the liquid /l/ by Arabic speaking children is attributed to their relatively high frequency and high functional load in function words in adult input (Amayreh, 2003; Amayreh & Dyson, 1998, 2000). Children also produced sounds which are not part of Arabic inventories such as [p], [ts], [ŋ], [ł], [pf], [β], and [θ]. The acquisition of emphatics is later and is completed by age eight. These are physiologically more complex sounds because they involve a secondary articulation. For example the emphatic / t/ is produced by both contact of the tip of the tongue behind the alveolar ridge and raising the back of the tongue.

In testing Palestinian children's ability to isolate phonemes in reading development in a diglossic context, Saiegh-Haddad (2007) found that first graders were better able to isolate phonemes in their dialect than those unique to MSA. She also concluded that both Arabic phonological structure and orthographic representation, which favors the syllable (consonant-vowel combinations) rather than single sound units, explain children's difficulty to isolate initial phonemes.

Milestones in Word Comprehension
Findings from word comprehension in Arabic are in line with the developmental sequences reported in other languages. Egyptian children were able to understand the affirmative/negative contrast, the active/passive contrasts, gender marking of nouns, and prepositions representing in, on, beside, and under before age three. Numbers beyond number two do not seem to be acquired before six when children enter school (Omar, 1973). Al-Akeel (1998) tested Saudi children's comprehension of possessives and prepositions, and concluded that possessives are understood before age three while the comprehension of prepositions spans from three to six. This is comparable to orders reported for English acquisition except for the prepositions under and between which are comprehended earlier in English (3 and 3:6 respectively). Saudi children understood /fi/ 'in' and / ʢ ælæ/ 'on' before age three; /tæ ћt / 'under', /žæ n b/ 'beside', /wæ ra/ 'behind', and /gudæm/ 'in front of' between the ages of four and five and lastly, /be:n/'between' after age six. Agentless passives (e.g., the ball was hit) were understood at age three while reversible passives with animate agent and patient (e.g., the boy was seen by the girl), were comprehended beginning at age 4:6 (four years, six months).
 
Milestones in Production
Acquisition of Negation and Interrogation: Three stages in the acquisition of negation are identified. First /læء/ 'no' is used appropriately but also inappropriately overgeneralized to express all types of negation. It is attached to the sentence without modifying it. In the second stage, children add the negative particle /miš/ and tag it to their utterance. In the final stage, children use the discontinuous negative particle / mæ...š / appropriately affixed to the verb.

In discussing the acquisition of negation by Palestinian children aged 1:10 to 2:7, Mohamed and Ouhalla (1995) noted that children treated nominal sentences in Arabic which are equivalent to the existential sentence in English but with no verb differently from verbal sentences. These generally comprise a noun and an adjective as in / kebira lkura/ 'the ball is big'). Children used the negative particle m-š in front of both nominal and verbal sentences. While this is the correct pattern for nominal sentences, verbal sentences are negated following the pattern m-Verb-š with the negative particles prefixed and suffixed to the verb. The authors concluded that children at this stage have not yet developed the obligatory verb movement responsible for a productive derivation of the form m-Verb- š in adult Palestinian Arabic. During the early stages of negative acquisition, children express only negation that carries meaning, while acquisition of negation falling under functional categories is still missing.

The same developmental stages are observed with questions (Omar, 1973). First, questions are signaled by rising intonation, then by tagging question words to either the beginning or ending of utterances and finally by using interrogative words with prepositions and adult stylistic placement of question words in various positions in the sentence. Friedman and Costa (2007) studied the acquisition of word order among Palestinian Arabic speaking children and found a clear preference in repetition tasks for the Verb-Subject (VS) order before age two for both transitive and intransitive verbs (i.e. verbs that take object complement such as 'hit' and those that don't such as 'sleep'). In the second stage (2:6) children's repetitions were similar for both VS and Subject-Verb (SV) orders.

Milestones in Morphology Acquisition
Noun Phrase Inflections. Given the complexity of plural markings in Arabic, children first express the concept of plurality by using modifiers such as /kulluhum/ 'all' before the singular form, or a numeral followed by a singular noun /tlata ktab/ 'three book', or repeating the singular noun by using a coordinate noun phrase, for example, /di gutta w di gutta/ 'this is a cat and this is a cat' (Omar, 1973). By 1:8, children produce plurals using all plural markings. In both longitudinal and experimental studies, Ravid and Farah (1999, 2001) found that, at around age two, Palestinian Arabic speaking children use the broken plural category the most (for example, singular /kitab/ 'a book' /kutub/ books). These are irregular forms which are quite frequent in vocabulary items used with children and are used as unanalyzed rote forms. They are followed by the regular feminine suffix /-at/ plural marker (for example, singular /kura/ 'a ball,' plural /kura:t/ 'balls'). However, the masculine regular plural suffixed forms ( nominative /u:n/ and genitive /i:n/) are rare because they are generally restricted to animate nouns as in the singular noun /mudarris/ 'teacher' is pluralized as /mudarrisu:n/ 'teachers' in subject position and 'mudarrisi:n' in object position. These account for only 2% of all plural forms in the basic lexicon and are the latest to develop at around age 2:6. Arabic also has a plural form for duals (two). Its use is generally limited to body parts pairs (two hands, two feet, etc.). Collective (non count) nouns are acquired relatively later and are rare. By age three, the regular plural marker seems to reach its peak productivity while irregular forms become productive at a much later age.

Two types of overgeneralization errors in acquiring plurals are noted. First, children overgeneralize the regular feminine marker /–at/, which is the least constrained semantically and formally, to broken plural forms. Later, beginning around 2:5, they overgeneralize broken plural patterns to adult sound feminine plural nouns. The masculine sound plural, the dual, and the collective forms are produced later and with no errors suggesting that they are not yet productive in the child's system. The early broken plural patterns are rote learned forms and later erroneous irregular patterns with irregular nouns, suggest that children organize irregular plurals in subclasses of schemas (Ravid & Farah, 2001). These errors continue well beyond age seven. In addition, the highly irregular plural agreement in Arabic noun phrases delays its acquisition to around age 12 (Moawad, 2006). In contrast, the regular gender agreement is produced correctly as early as age 2:8.

Verb inflections. Kuwaiti Arabic children aged 2 to 2:6 produced verbs with perfective markings earlier than imperfective markings (Aljenaie, 2001). They also overgeneralized first person singular inflections and used the third person singular marking before the second person and plural affixes. Masculine marking of the verb appeared before the feminine affixes. Aljenaie explained the absence of unmarked stems by claiming that children are constrained by Universal Grammar from producing non-adult bare stems and do not construct 'wild grammars'. As in other languages suffixed markers (gender and number) are produced earlier than prefixed (tense/aspect) ones.

Derivational morphology. Data from 3:5- to 9:9-year-old children acquiring Moroccan Arabic shows that children develop both horizontal and vertical derivational strategies that allow them to form words from their roots and from other surface forms (Badry, 1983, 2004). Children go through four main stages in acquisition of verbal and nominal pattern derivations. Badry found that the causative pattern was the first to be used productively by children followed by the reciprocal then the middle voice patterns. Children at all ages studied used Pattern 1 (fa ʢ ala) "to express several semantic and syntactic relations in spite of the availability, in their repertoire, of more specialized verbal patterns (Badry, 2004, p. 140). Errors were with verbs derived from defective roots. Children tended to supply a third consonant or metathesize consonantal roots. Such errors were interpreted as evidence for the psychological reality of the root in the process of word formation.

Another study compared vocabulary size of bilingual Arabic-French Lebanese children with their monolingual counterparts. Children's ages ranged between 17-19 and 26-28 months. The monolingual Lebanese Arabic speaking children's vocabulary size was smaller and had a higher percentage of verbs than that of bilingual or French monolingual groups. These differences were attributed to both the rich morphological structure of Arabic and parents' socioeconomic background (Zablit & Trudeau, 2008).
 
Conclusion

The study of the acquisition of Arabic, a Semitic language, promises to contribute to the cross-linguistic study in psycholinguistic research. Such research allows the testing of hypotheses, which were mainly based on the study of English and other European languages, about universal and particular features in language development. Additional areas of research in literacy development, bilingualism and speech pathology have opened up recently, which is a positive step for research concerning language development among Arabic children.