1.1 On the cartography of the Hebrew left periphery

Intensive cartographic research over the last two decades led to a detailed map of the higher (so-called left) part of the clause along the lines given in (5) for Italian/Romance (schematic description adapted from Rizzi & Bocci 2017):³

Assuming the inventory of functional positions in the left periphery in (5), let us now review some fundamental aspects of the rich map of the periphery of the clause in Hebrew, which will offer some guidance for the interpretation of the developmental findings.

Force > Top (embedded declaratives introducer above topic)

Starting from the uppermost part of the tree, Force is the highest head in Hebrew. This can be seen in the distribution of the complementizer and embedding marker she-, marking declarative force. The examples in (6) show that she- in Force is higher than Top. (6a) demonstrates this for the declarative embedding marker, which precedes the topic, and (6b) shows the same order for the relative complementizer, preceding a resumptive pronoun⁴ in topic position, an available option in object relative clauses in Hebrew. The opposite order (Top > she) would give rise to ill-formedness, as demonstrated by the ungrammatical (6’). So the order Force > Top is established.⁵

Int > Top (embedded interrogative yes/no question marker above topic)

The introducer of embedded yes/no questions (the interrogative marker im) also precedes the topic in Hebrew, an order that is visible in embedded interrogatives with topicalized elements. The order in (7), in which im precedes the topic, indicates that the position that is occupied by Int in the surface is higher than the Top position. The point is confirmed by the ungrammaticality of (7’), with Int following Top.

We keep Force and Int separate as in (5) because cross-linguistic evidence shows that Int can in fact be lower than the declarative Force marker (Rizzi 2001; 2013a). Nevertheless, the distinction does not play a critical role in the Hebrew map: we follow Shlonsky’s (2014) analysis and assume that im in Hebrew moves from Int to Force, hence it always ends up occupying the highest peripheral position on the surface.

Top > Q (topic above wh questions)

Top, in turn, is higher than Q, the position to which the Wh element of root Wh questions moves.⁶ One central property that emerges, language after language, is that when a topic and a Wh phrase co-occur they do so in the order Top > Wh.⁷ Hebrew is no exception with regard to this property (see also Shlonsky 2014), as illustrated by the minimal pair in (8), containing a contrastive topic, where the sentence is grammatical with the topicalized object preceding the wh-element (8), but ungrammatical in the reversed order (8’):

Int > Q (why questions above other wh questions and above topic)

Lama (why) clearly differs from other Wh elements in Hebrew in that it precedes the topic:

The orderings Why > Top and Top > Wh in (8)–(9) clearly show, by transitivity, that lama occupies a position higher than the position of other Wh elements. On the basis of different kinds of evidence, Rizzi (2001) proposed that perché (why) in Italian occupies the position of Specifier of the head Int, higher than Q in (5), and also used to express if-type elements, introducing yes/no questions. If the Spec/Int hypothesis is extended to lama in Hebrew, the contrast (8)–(9) is captured, and confirms the ordering Int > Q for Hebrew, already established (by transitivity) in (7).⁸

Q > Adverb in Mod > subject in IP

Adverbs can be preposed to the LP, and they appear to be hosted in a dedicated position, Mod(ifier), a position distinct from Top (Rizzi 2004). To examine the position of Mod within the LP, we first select adverbs that do not easily topicalize and therefore best illustrate movement to Mod. We then examine the position of such adverbs relative to other layers. Suddenly (pitom) seems to be such an adverb: Suddenly can appear in the left periphery, as indicated by its position before the subject in (10). To the extent that the subject delimits the highest part of IP, the occurrence of the adverb before the subject shows that Mod is in the left periphery.

Mod necessarily occupies a low position in the LP, in fact lower than Q – the position occupied by Wh elements for argument Wh questions as in (8) (and some adjunct, but not why, questions, see discussion above), as shown by the following contrast between (11) and (11’), demonstrating that suddenly can follow Wh but cannot precede it.⁹

Force, Int, Top, Q, Mod > Fin

In Hebrew there is no overt morphological marker for the Fin head, lexicalizing the Fin position. We take the surface position of the inflected verb in inversion structures as the manifestation of Fin. Following much current literature starting from Shlonsky (1997), we assume that the inversion between the subject and the inflected verb is licensed by the movement of another element to the left periphery. More specifically, we assume that an element that moves to the front passes through Spec of Fin, where it allows for head movement of the inflected verb, much as in V2 type phenomena.¹⁰ Adverbs (12), Wh elements (13), topics (14), and relativized phrases (15a) all pass through spec Fin, where they license movement of the finite verb to Fin, and then continue to their final destinations, where they get their scope-discourse interpretation.

We can observe in (12) that the adverb in Mod can precede the preposed finite verb, in Fin, which precedes the subject (in the higher part of IP). This order shows that Mod is higher than Fin.

The same point can be made about Q and Top. We can observe in (13) and (14) that the Wh element in (13) and the topic in (14) precede the preposed finite verb, in Fin, which precedes the subject. This order establishes that Q is higher than Fin and that Top is higher than Fin. (and, by transitivity, given that Int is higher than Top (7), Int is higher than Fin as well).

Verb inversion is possible in Hebrew after the relative complementizer she- (15), establishing Force above Fin (relative complementizers are very high in the structure of the LP, in a position close, or identical to Force, Rizzi 1997; see a more detailed discussion on the analysis of relative clauses below in Section 4.3.1). Interestingly, as shown in (15’), inversion is impossible after the sentential embedding marker she-. We assume that the difference between the two types of she- stems from the fact that in relative clauses, but not in sentential complements, there is a licenser passing through Spec Fin, the relativized phrase. Under the raising analysis of relative clauses, the relativized NP (the relative “head” in traditional terminology) moves through Spec-Fin, hence allowing the finite verb to move into the Fin head. In contrast, in sentential embedding, inversion is unavailable under the embedding marker she- because in sentential complements there is no movement involved, hence there is no passing through Spec-Fin, consequently the movement of the verb to Fin is not licensed.¹¹,¹²

Relative complementizer (Force) > Fin

In conclusion, Fin is the lowest head within the LP, preceded by all other left peripheral positions identified, Force, Int, Top, Q, and Mod. The above empirical observations yield the order Force > Int > Top > Q > Mod > Fin in the Hebrew LP. The emerging design of the tree is depicted in Figure 1.

Figure 1

Map of the functional sequence of the clause in Hebrew.

It is interesting to note that the order that emerges from the distributional evidence in Hebrew is essentially the same as the one found for Romance as in the schematic representation in (5) above, as well as cross-linguistically (Japanese, Saito 2012; African languages, Aboh 2004, and more). This is to be expected under uniformity guidelines (Chomsky 2001).

2.1 Summary of Friedmann and Reznick’s results

Friedmann and Reznick examined the order of acquisition of various syntactic constructions in Hebrew, using a sentence repetition task in which 60 monolingual typically-developing Hebrew-speaking children aged 2;2–3;10 repeated 80 sentences each, and an analysis of the spontaneous speech of 61 (other) children aged 1;6–6;1 (56 who were recorded once and 5 whose longitudinal data were recorded and analysed), which included a total of 27,696 utterances.

The sentence repetition task included structures with A-movement, which were sentences with unaccusative verbs in SV order, three types of sentences derived by A-bar movement: subject relatives, object relatives, and topicalization structures, and sentences involving verb inversion in adverb-VS order with unergative and transitive verbs. The test also included SV sentences with unergative and transitive verbs, which were matched in words, length and number of words to the structures with movement, in order to control for extra-linguistic cognitive factors such as memory and attention (for more details see Friedmann & Lavi 2006). The spontaneous speech analysis encompassed a very wide variety of sentence structures. In the current analysis, we focus on SV sentences with unergative/transitive verbs, VS and SV sentences with unaccusatives, Wh questions of various types, relative clauses, topicalization structures, and finite embedded sentences. Following predictions emerging from our new account, we also analyze root yes/no questions, why questions, and preposed adverbs

Data gathered through both methodologies were analyzed using the concept of Guttman scale (Guttman 1944; 1950), which revealed the order of acquisition of the various structures. Guttman scales allow for the identification of implicational relations between properties. For example, if properties A and B are organized in a Guttman scale, then if property B is there, property A has to be there as well, but the implication does not necessarily hold in the opposite direction: if property A is there, B may or may not be there. For example, if an exam includes a hard question that requires mastery of three areas of knowledge, a person who answered this question correctly would probably be able to answer a question that involves just two of the three areas. A person who answers correctly a question that requires mastery of two areas would probably be able to answer a question that requires only one of the areas. This creates a Guttman scale between the three questions. Another example may come from number cognition – a child who can count to 100 would also be able to count to 10. A child who can count to 10 would also be able to count to 4. The other direction would obviously not work: not all children who can count to 4 can also count to 10 or 100. These three levels of capacity form a Guttman scale.

In these examples, one capacity includes the other as a subpart, or implies the other. There is a conceptual parallelism between the growing trees logic and the Guttman scale. If we think of structure building as occurring from lower to higher layers, under the growing trees view, higher parts of the tree necessarily include lower parts, and the acquisition of the higher parts would necessarily imply the acquisition of the lower ones.

Figure 2, reproduced from Friedmann & Reznick, provides a summary of the findings by these authors, and represents the take-off point for our Growing Trees approach. On the left is the Guttman scale produced from the analysis of the spontaneous speech samples, and on the right is the Guttman scale yielded from the repetition of the various types of movement.

Figure 2

A summary of the findings from Friedmann & Reznick (this volume): Production profiles of various structures, ordered by stage of acquisition giving rise to a Guttman scale. Left: spontaneous speech samples. Right: sentence repetition (%correct). Blue (dark shaded) cell: the child masters the structure (in repetition: at least 80% of the sentences of this structure were repeated correctly; in spontaneous speech: at least one such structure appeared in the child’s sample). Grey (lightly shaded) cell: the sample did not include a relevant verb. Reproduced from Friedmann & Reznick (this volume).

The sentence repetition task revealed a set order of acquisition of three types of syntactic movement: the first structures to be mastered (i.e., at least 80% of the sentences repeated correctly) are A-movement (of the internal argument of unaccusative verbs to subject position) together with simple SVO sentences, then A-bar-movement to the left periphery (represented in the repetition task by relative clauses and topicalization structures) are mastered, and finally comes movement of the lexical main verb from I to C. Relative clauses and topicalization structures were acquired together. There was no correlation with age. Crucially, the order of acquisition forms a perfect Guttman scale, as summarized in Figure 2: four children were unable to repeat any structure; 21 children were able to repeat sentences with A-movement but not sentences with A-bar or I-to-C movements; 27 children could repeat both A- and A-bar movement structures, but not I-to-C structures; and 8 children could repeat all three structures: sentences with A-movement, A-bar movement, and I-to-C movement. There was no child who could repeat I-to-C but not A- and A-bar movement, and no child who could repeat A-bar movement but not A-movement.¹³

The analysis of spontaneous speech revealed the same order of acquisition, and provided further insights into the order of acquisition within the group of constructions with A-bar-movement, and their relation to the acquisition of sentence embedding. Similarly to the repetition task, age was not a good predictor of the acquisition of the various syntactic structures, as different children acquired the same structure in different ages, but the order of acquisition was uniform across children irrespective of their age: 1) A-movement of the internal argument of unaccusative verbs to subject position appears first – first occurrence in the corpus at age 1;10 (and 1;7 in the longitudinal data). (From age 2;2 all children who produced an unaccusative verb also used SV order with it). SV order with unaccusative verbs appeared together with simple sentences in SV(O) order with unergative and transitive verbs; 2) The next instances of movement to appear are argument Wh questions, i.e., subject- and object questions, including object questions inquiring about the verb phrase (‘what are you doing’) and some adjunct Wh questions (e.g., where), with no difference between subject and object questions or between argument and adjunct questions (of the types that appeared at that stage) – Wh questions first occur in the analyzed corpus at age 1;6, stabilizing at age 2;5 (by “stabilizing” we mean that more than 80% of the children already used them, in this case 92% of the children used Wh questions from age 2;5); 3) In the next stage, relative clauses (headed and free relatives), and topicalization structures appear together, again with no difference between subject and object dependencies. Importantly, this stage is concomitant to the appearance of sentence embedding of both declarative and interrogative embedded clauses. (Notice that we discuss here only adultlike embedding, and not other forms such as so-called “preconjunctionals”, Penner & Mueller 1992). These structures first appear at age 2;5–2;6 and stabilize between the ages 3;3 and 4;0 years; 4) Last comes movement of the lexical verb (beyond “do”, see footnote 13) to C, which appeared only in three children, the youngest of whom was 5;7.

Here, too, the Guttman scale was very robust, with 6 children showing none of the structures; 7 showing simple SV with unergative and transitive verbs, and SV, as well as VS, with unaccusative verbs; 9 children who produced SV sentences as well as Wh questions; 34 who produced SV sentences, Wh questions, as well as relative clauses/topicalization/embedded clauses. (Three of these 34 children, the bottom 3 in Figure 2, produced all the above as well as I-to-C sentences with a lexical verb.) Only a single child of the 56 did not conform to the Guttman scale, as his sample included relative clauses and embedded clauses but no Wh questions.

2.2 New questions emerging from the data

The results from the spontaneous speech analyses and from the repetition task yield a converging picture regarding stages of acquisition: SV structures, including those derived by A-movement with unaccusative verbs, are acquired first, then Wh questions are acquired, and then relative clauses, topicalization structures, and sentential embedding structures are acquired together.

The three stages emerge in a robust and crystal-clear manner, as shown by the fact that the relevant clusters of constructions can be neatly organized in Guttman scales. These results raise further theoretical questions, though:

1. Why does A-movement, illustrated by SV order with unaccusative verbs, occur before any instance of A-bar movement?

2. Why are Wh questions acquired about one year (with individual variation) before other A-bar structures such as relative clauses and topicalization?

3. Why are topicalization, relative clauses, and clausal embedding acquired at the same time?

It is hard to capture the three structures mentioned in question 3, topicalization, relative clauses, and clausal embedding, as a natural class in terms of properties like embedding and movement: two (relative clauses and sentential embedding) are embedded structures and the other is not; two (topicalization and relative clauses) involve movement, but the other does not.

Our goal in the present paper is to provide a principled basis for the analysis of the three stages, also addressing the puzzles just mentioned. The key ingredient is the cartographic representation, which offers a fine-grained hierarchical structure detailed enough to draw the required distinctions. We propose a “Growing Trees” approach by which the map of the left periphery is acquired gradually, starting from the lower layers, and then moving to higher layers.

In the next section (Section 3) we present our Growing Trees account and show how it captures the three stages emerging from Friedmann and Reznick (this volume) just described. We then discuss each stage in detail (Sections 4.1–4.3) and illustrate further predictions that can be derived from the cartographic map and examine them empirically through further analyses of the corpus. These cartographically-guided analyses will allow us to investigate further the difference in acquisition of root and embedded questions (Section 4.3.1), address the status of yes/no questions compared to Wh questions (Section 4.2.2), and revisit the acquisition of why compared to other types of Wh questions (Section 4.3.2.1). The approach will also allow us to suggest an analysis of the stage of acquisition of sentence-initial adverbs (Sections 4.2.1 and 4.3.2.2). In Section 4.4 we show how the findings replicate in longitudinal data. The approach also predicts no asymmetry in production between subject- vs. object relatives, and subject- vs. object questions, such lack of difference is indeed found in the data (Section 4.5). We conclude Section 4 with an open question regarding a possible stage preceding Stage 1 (Section 4.6).

4.1 Stage 1. VP and IP

In Stage 1, children have acquired VP and IP (see Figure 4), and this enables them to get the SV order with unaccusative verbs (in addition to the VS order). Given the unaccusative hypothesis (Perlmutter 1978; Burzio 1986), SV order with unaccusative verbs involves movement of the internal argument from its thematic position. The availability of I, endowed with attracting features, makes spec IP available, and allows the children to move the DP from the thematic position internal to the VP to the subject position of the clause in spec IP.

Figure 4

Stage 1 of the growing tree.

The existence of SV order with unaccusative verbs, then, provides explicit evidence for A-movement. The occurrence of this structure in our Stage 1 supports the view that A-movement is available from early stages (as claimed in Pierce 1992; Snyder et al. 1995; Sano et al. 2001; Adragão & Costa 2004; Lorusso et al. 2005; Friedmann 2007; Shimada & Sano 2007; Costa & Friedmann 2009; 2012; Friedmann & Costa 2011; and contra approaches like Borer & Wexler 1987; Babyonyshev et al. 2001; Machida et al. 2004; Wexler 2004).

In the data of children who are at Stage 1 we see that they produce unaccusative verbs in both SV and VS orders. The data in our corpus also provide direct evidence that children distinguish between unaccusatives on the one hand and unergatives (and transitives) on the other. At this stage, only with unaccusatives do we also find the VS order, which is the order of merge according to the unaccusative hypothesis (Perlmutter 1978; Perlmutter & Postal 1984; Burzio 1986; Belletti 1988). It is only at Stage 3 (or later) that we find VS order with unergatives and transitives, which, in Hebrew, is a function of I-to-C movement. This finding is in line with data from Italian, Hebrew, and European Portuguese showing early access to the identification of the unaccusative class, and the distinction between unaccusative and unergative verbs (Adragão & Costa 2004; Lorusso et al. 2005; Friedmann 2007; Costa & Friedmann 2009; 2012; Belletti & Guasti 2015; Belletti & Bianchi 2016).

Another consideration is relevant here. Chomsky (1995; 2000) traced back movement to the fundamental structure-building mechanism. Structure building that incorporates an element from outside the structure is “external Merge”, and structure building that uses internal building blocks – elements that have already been incorporated into the tree – are instances of “internal Merge”; internal Merge is commonly referred to as “movement”. This approach suggests, then, that movement and structure building are fundamentally the same: both are instances of Merge.¹⁴ Our data is consistent with this unified view of Merge, as we could not identify a “pre-movement” stage, in which structure building is available, but movement is not yet acquired (see our further discussion of this point in Section 4.6).

4.2 Stage 2. The lower field of the left periphery

From Stage 2 on, we start seeing evidence that part of the structure of the left periphery became available (See Figure 5). The first manifestation of movement to the LP is the early production of Wh questions. Given current cartographic analyses of different languages (see Rizzi 1997 footnote 4; Rizzi & Cinque 2016; Rizzi & Bocci 2017), the lower part of this LP configuration includes the landing site of argument- (and some adjunct-) Wh questions. This appears to be valid for Hebrew as well, as shown in Section 1.1, see Figure 1. Hence, under the Growing Trees account, the occurrence of Wh questions is expected as soon as the relevant part, the lower part of the left periphery, becomes available, in Stage 2.

Figure 5

Stage 2 of the growing tree (also including the structures acquired in Stage 1).

At this stage, the children produced root argument Wh questions of various kinds: subject, object, PP object, object questions inquiring about the verb phrase (‘what are you doing?’), as well as adjunct where (and a few where-to and when) questions. All these questions appeared at the same stage, without difference between subject and object questions (for similar findings regarding no difference between subject and object questions in early acquisition see Eyal 1976; Stromswold 1995).

4.2.1 From acquisition data to linguistic analysis: Preposed adverbs

Another head that is included in the map of the lower field is Mod. If preposed adverbs move to spec-Mod, then we expect them to also appear in Stage 2, together with Wh questions. And this is precisely what our data show: of the 12 children who were at Stage 2, five indeed produced sentences with preposed adverbs (see example (16); none of the Stage 1 children did). Table 1 summarizes all the data analyzed for the three stages, column “preposed adv” lists the appearance of preposed adverbs for each of the analysed samples.

Table 1

The acquisition of the various structures organized by stage in which the structure is acquired, and ordered by the stage in which each child has acquired it (rather than by age). Each row summarizes the production of a different child, a blue (shaded) cell indicates that the child produced this structure; a white (unshaded) cell indicates that the child did not produce any instance of this structure; a grey cell means that the corpus of this child did not include any verb of the relevant type (for example, the corpus did not include any unaccusative verb).

1. (16)

1. Axshav
2. now
1. ani
2. I
1. ekax
2. take.FUT
1. et
2. P.ACC
1. ha- dag
2. the-fish
1. ha- ze. (Uri, 2;5)
2. the-this
1. ‘Now I will take this fish.’

4.2.2 From acquisition data to linguistic analysis: The derivation of yes/no questions

As we discussed above, acquisition data may shed light on theoretical questions. The observed properties of the acquisition of Stage 2 provides a case in which data from acquisition may inform theory, here pertaining to the derivation of yes/no questions.

In principle, three possibilities exist with respect to the representation of the yes/no feature in the syntactic tree: no feature in the LP, a feature in Q, or a feature in Int. If the language allows for yes/no questions without an overt morpho-syntactic yes/no marker, and the interrogative interpretation is uniquely expressed through a special intonation at PF, one conceivable option would be that there is no yes/no feature in the LP: the assignment of a special intonational contour could be triggered by an IP-internal featural specification. A second possibility is that the yes/no feature resides where the Wh operator resides, in Q, which is in the lower field of LP. A third option is that the yes/no feature in main questions resides where it resides in embedded yes/no questions, in Int, in the higher LP zone (Figure 1).

A way to inform the decision between the three options would be to examine whether yes/no questions are acquired with declarative SV sentences (which would support the no-feature-in-the-LP option), with root Wh questions (which would support the feature-in-Q option), or with embedded yes/no questions (supporting the feature-in-Int option).

In order to address this question, we conducted an analysis of the corpus used in Friedmann & Reznick (this volume), with the same method. Using speech samples of 56 children (for detailed description of the methodology for data selection and analysis see Appendix A), we analysed, for each child, the structures that were already present in their sample, and looked for a hierarchy of acquisition of the various structures between children. In the logic of Guttman scales, if we found that there were samples that included only structure A, samples that included structures A and B, but no samples that included only B, we could conclude that A is acquired before B.

The results, summarized in Tables 1 and 2, were that yes/no questions appeared later than declarative SV sentences, earlier than embedded yes/no questions, whereas we could not determine any order of precedence between yes/no questions and root Wh questions: in the samples of the 56 children in Table 1, none of the children in Stage 1 produced yes/no questions (neither did they produce wh questions), and 9 of the children in Stage 2, the stage in which Wh questions appear, produced yes/no questions without any indication of the higher LP (no relative clause, topicalization, or embedding, and crucially, no embedded Wh question). This suggests that yes/no questions are acquired at Stage 2, together with root Wh questions. Is there any order of precedence between Wh and yes/no questions? The data, summarized in Table 2, indicated no precedence between the two, namely, there was no Guttman scale for Wh and yes/no questions. All but one of the ten children in Stage 2 for whom we had raw data for analysis of this issue produced both Wh and yes/no questions.

Table 2

The pattern of acquisition of root and embedded Wh and Y/N questions.

We also performed a further analysis considering the longitudinal data of two more children who were recorded bi-weekly. Here we could assess, for each child, when yes/no questions first appeared relative to the other structures. The longitudinal data yielded similar results, as shown in Tables 3 and 4 (to be discussed in detail in Section 4.4): for both children, when they were at Stage 1 they produced no questions, and then at Stage 2 they produced both Wh and yes/no questions, both appearing within two weeks, with no structures that belong to Stage 3 yet.

Table 3

A growing tree: Longitudinal data – Hagar.

Table 4

A growing tree: Longitudinal data – Leor.

An additional indication for the close proximity between the appearance patterns of the two types of questions can be seen when analyzing the time of first appearance of each question type in the longitudinal data of nine children (see Appendix A). These data indicate that 3 children produced a Wh question before a yes/no question, 3 had them simultaneously, and 3 started using yes/no questions before Wh questions, all within 6 weeks.

Taken together, the 56 children’s speech samples as well as the longitudinal data indicate that yes/no questions are acquired together with Wh questions in Stage 2, both appear later than Stage 1, where children produce declarative SV sentences, and before Stage 3 where they produce embedded questions (and embedded declaratives, relatives, and topicalization)

The finding that yes/no questions appeared simultaneously with root Wh questions supports the possibility according to which the yes/no feature resides in Q, in the lower LP layer. One possible implementation would be to assume, following much literature, that a null yes/no operator is present in polar questions, the null counterpart of the overt Wh operator in Wh questions. This null operator would reside in the specifier position of the Q head, in the lower part of the LP. Once this position becomes available, it may attract a Wh operator, or host a yes/no operator.

4.3 Stage 3. The higher field of the LP

In the next stage, Stage 3, the higher field of the left periphery becomes available (see Figure 6). This allows for the appearance of relative clauses and topicalization structures, together with sentence embedding. As summarized in Table 1, in line with the Guttman Scale implicational logic, all children who were at Stage 3 and produced any of Stage 3 structures (relative clauses, topicalization, sentential embedding) also produced some structures that belong to Stage 2 (root Wh/yes no questions and Adverbs in Mod), and SV sentences, which belong to Stage 1. The same Guttman scale could be seen also in the repetition task: all children who could repeat correctly the relative clauses and the topicalization sentences could also repeat the SV sentences (with unaccusative and unergative/transitive verbs).

Figure 6

Stage 3, the final stage of the growing tree (also including the structures acquired in stages 1 and 2).

It is not surprising that relative clauses appear together with sentential embedding, because relative clauses are embedded clauses. A more surprising property of the natural production data of this stage is the finding that the appearance of root topicalization structures coincides with the appearance of embedded clauses, as topicalization is a typical main clause phenomenon, much as root question formation. We suggest that the co-occurrence of the three constructions is a straightforward consequence of the fact that they all involve positions in the same left peripheral area, constituting the higher field of the LP.

4.3.1 Embedded declaratives, embedded questions, and the selection of clauses

Let us concentrate now on embedding, starting from the most straightforward case, the embedding of selected declarative clauses. A natural assumption about selection is that the selection of finite embedded clauses is categorially uniform, with the selected property expressed in the highest position of the complementizer system. Namely, all verbs selecting a finite complement select a ForceP, in which the selection properties of different verbs are expressed: say selects +declarative, wonder selects +interrogative, surprise may select +exclamative. This follows from the classical theory of selection in which selection is satisfied under sisterhood (Chomsky 1965). In minimalist terms, this amounts to saying that external Merge only sees the labels of the categories that undergo Merge and cannot penetrate lower positions, internal to the structure being merged. Therefore, selection does not work through Agree-like relations, which could take place at a distance. In sum, selection (of finite clauses)¹⁵ requires the projection of the whole structure up to the Force layer.

Embedded declaratives in Hebrew are introduced by the embedding marker she-, which expresses both declarative force and finiteness. We assume that she- is in Force, satisfying the selectional properties of the matrix verb. This relation between force and finiteness could be expressed through an Agree relation between Force and Fin.

As for (finite) relative clauses, they are also introduced in Hebrew by the complementizer she, much like Romance che and que, English that (see Kayne 1976, for the classical analysis of the introducer of the relative clause as a complementizer). So, the natural assumption, along the lines of Rizzi (1997), based on Romance distributional evidence, is that the complementizer introducing relative clauses also occurs in the highest position of the CP system, in Force, as illustrated in the Hebrew cartographic description in Section 1.1 above (Figure 1).

Figure 7 spells out our basic assumptions with respect to relative clauses. As for the position of the nominal head of the relative clause, we adopt a raising analysis, along the lines of Bianchi (1999) developing Kayne (1994), with D externally merged higher than ForceP. The relative NP moves to the specifier of Force. The Force head of a relative clause is endowed with a +R feature, the criterial feature attracting movement of NP into its specifier.¹⁶

Figure 7

The cartographic structure of relative clauses in Hebrew.

The discussion of selection anchored in Force also directly pertains to embedded questions, which are selected clauses as well. Under the general theory of selection that we are assuming, the selection of embedded questions will also occur in Force. This would mean that in Force there is a question feature. Many languages provide evidence that the Wh element or the embedded yes/no question marker in fact occur in a position lower than the embedded Force head (Puskás 2000; Rizzi 2013a). So, we follow the analysis in Rizzi (2013b) and assume an Agree relation between the embedded Force (selected by a higher verb) and Q (for embedded Wh questions), or Int (for embedded yes/no questions). The essential point is that under the simple and general view of selection, embedded questions will be accessible to the child at a stage in which the whole CP structure is available, including the highest layer that contains Force. This predicts that embedded Wh questions and embedded yes/no questions would appear together with embedded declarative sentences, all selected by a higher selector – a higher verb in the case of declaratives and questions (and plausibly the determiner in the case of relative clauses). And indeed, this is the picture emerging from natural speech, as shown in Table 2: embedded Wh questions appear exactly at the same time as embedded declaratives, in Stage 3.¹⁷ Embedded whether/if questions also appear in this stage, with the usual individual age variation (e.g., one girl produced yes/no questions already at 19 months, and another at 35 months).

It is crucial to notice that Stage 3 is not only an “embedding stage”. We have already mentioned that root topicalization structures appear in Stage 3. This follows from the cartography of the CP system, in which positions hosting topics cross-linguistically appear in the higher field (see our cartographic Section 1.1 above demonstrating this order for Hebrew).¹⁸ In the next section we show that another non-embedded construction, root why questions, also appears in Stage 3.

4.3.2 From the Growing Trees approach to new data on acquisition

4.3.2.1 Why questions

A look at the map in Figure 1 highlights another non-embedded construction that crucially involves a position in the higher field of the LP, and hence is predicted to appear at Stage 3: Why questions. The Wh element why has been shown to occur in a position distinct from, and higher than the Spec/Q position hosting other Wh elements (Rizzi 2001). We have shown in example (9) above,¹⁹ that this is the case in Hebrew as well: lama (why) appears above TopP, like the embedded yes/no marker im (if). This is similar to Italian, where perché (why), like the embedded yes/no marker se (if), can precede a topic (in main and embedded clauses). This observation supports the hypothesis that lama (and perché) and im (and se) occupy the layer Int, higher than the landing site of other Wh elements, Spec/Q (see Thornton 2008 for supporting developmental data from the acquisition of English, and Thornton 2016 for a discussion of the late acquisition of why questions; see various contributions in Soare, 2021, for cross-linguistic evidence supporting the special position of why). If why questions crucially involve Int, which is in the higher LP field, we predict why questions to appear only in Stage 3, when the Int position becomes available (see Figure 6).

This theoretical prediction led us to analyze the different types of questions in the children’s production, and to examine when why questions appear relative to the other types of Wh questions, and in which stage of acquisition the children who already produce them are.

The acquisition data, summarized in Table 1, clearly show that why questions are indeed acquired only at Stage 3. The production of why questions perfectly matched the acquisition of other structures that appear in Stage 3: CP embedding, topicalization, and relative clauses, and does not appear for children who produce Wh questions but do not yet show evidence for the acquisition of Stage 3.

There were 17 children who produced why questions, all of them were at Stage 3, as indicated by their production of CP embedding with she- (all of them produced embedded sentences, and all but two also produced relative clauses or topicalization structures). None of the children who were at Stage 2 or 1 produced any why questions.

It is worth noticing that the cartographic analysis predicts a split between why and all other (root) Wh elements, rather than a split between argument and adjunct questions because adjunct Wh elements other than why target the same spec-Q position as do argument Wh elements. The split why vs. all other Wh elements is supported by the acquisition data, with why questions acquired after all other Wh questions (argument and adjunct). The acquisition data indicates that where questions are abundant, from the very early questions the children produced; the children also produced, with lower frequency, how, when, and where-to questions. It is worth noting that why questions occur very frequently in the corpus once Stage 3 is achieved (17 of the 34 children in Stage 3 produced why questions), and once acquired they appear very frequently in each corpus (for example, Leor, one of the children who were recorded longitudinally, produced in a single recording at age 2;11 64 why questions). So, the late acquisition of why questions is not a function of its rarity in the children’s production but rather it is tightly related to the position of why in the LP. We also see that there is no slow increase in the use of why questions with age but rather a sudden appearance corresponding to the acquisition of Stage 3. (Anecdotally, parents often talk about “the why period”, which starts abruptly and opens up a stretch of many why questions).

The late acquisition of why questions (and of embedding) immediately refutes an alternative account according to which constructions that involve movement are acquired later than structures without movement because structures with movement are harder. Why questions, unlike other argument and adjunct Wh questions, presumably do not involve movement (Rizzi 2001).²⁰ Had the movement structures been acquired later than no-movement ones, we would have expected why questions to be acquired before, rather than after, other Wh questions. The data, however, shows the exact opposite order, with why questions being the last to appear. Similarly, clausal embedding does not involve movement, still, it appears in Stage 3, after Wh questions, which do involve movement (See Hamann & Tuller 2014, for embedding as a factor of complexity).

4.3.2.2 Adverb preposing and topicalization

We can now examine the data with respect to the relation between two types of preposing: adverb preposing and topicalization. In the cartographic section (Section 1.1) we saw that adverb preposing targets a dedicated position Mod, distinct from and lower than Top, which is targeted by preposed topics.

Given that Mod is lower than Q and given our stage typology, we expect Mod to be available in Stage 2 alongside Wh questions, whereas topicalization is only expected to be available in Stage 3. And indeed, the acquisition data manifest this distinction clearly: there were five children (of the 12 children in Stage 2) who produced preposed adverbs²¹ but still no structure related to Stage 3, in particular no topicalization structure. Conversely, no child produced topicalization structures without structures relating to Stage 2 (see Table 1).

The emerging picture of the three stages in structure acquisition is summarized in Figure 8.²²

Figure 8

The different stages as reflected in the corpus: Stage 1 in the table includes SV structures with unergatives and unaccusatives, SV and VS structures with unaccusatives; Stage 2 includes root Wh and yes/no questions and preposed adverbs; Stage 3 includes relative clauses, topicalization, why questions, and embedded declaratives and questions. (Blue cells in the table indicate that a structure belonging to this stage has been produced; ages reported in months).

4.4 Longitudinal data: The same stages of acquisition

The results summarized in Figure 8 were obtained through a look at different children and the structures each of them was already able to produce. This yielded the three stages of acquisition. Another way to examine stages of acquisition is to observe the order of acquisition of various structures within the same child, and examine which structure precedes which structure, and which structures appear at the same time. We examine here whether the stages observed in the group of 56 children, also with respect to the three new structures we examined in this section, were also observable at the longitudinal data within a child by analyzing the longitudinal data of the two most densely tested children reported in Friedmann & Reznick (this volume).

Method. We examined the acquisition of the various structures in the production of Hagar and Leor. Hagar was recorded 114 times between the ages of 1;7–2;11, with an average of 219 utterances per sample. Leor was recorded 79 times between 1;9–3;0, with an average of 297 utterances per sample. The total number of utterances analysed for these two children was 16,002. Their data are collapsed to one-month periods. For each of the children we examine when each of the structures appeared first in their spontaneous speech.

Results. The structures we examined were acquired at exactly the same order, creating the same stages of growing trees as identified in the group analysis.

The order of acquisition, summarized for Hagar in Table 3 and for Leor in Table 4, included a Stage 1 in which SV structures appeared (Hagar did not produce unaccusative verbs in Stage 1), and then Stage 2 with root Wh questions and yes/no questions, and then Stage 3 with relative clauses, topicalization structures, why questions and sentential embedding. Namely, the sample analysis was completely confirmed by the longitudinal analysis.

4.5 Not only structure: Intervention locality

A considerable body of experimental work shows that in many languages, including Hebrew, children cannot understand and produce certain object relative clauses, object topicalization structures, and object Wh questions before age 6 (Correa 1982; 1995; de Vincenzi 1991; de Villiers et al. 1994; McKee et al. 1998; Stavrakaki 2001; Friedmann & Novogrodsky 2004; Friedmann et al. 2009; Belletti & Contemori 2010; Friedmann & Costa 2010; Costa et al. 2014; Belletti et al. 2012; Biran & Ruigendijk 2015; Bentea 2016). The results that emerged from the spontaneous speech samples seem prima facie to contradict these earlier findings, in two important ways. Firstly, these three structures appear early in our samples, with some children producing object questions as early as one year and a half, and some producing object relatives and topicalization structures around age two and a half. Secondly, whereas previous work consistently found subject-object asymmetries, with object dependencies significantly harder to understand and produce than subject ones, the natural data samples showed that subject- and object relatives appear together, and so do subject- and object questions.

How can these seemingly contradicting data be reconciled? We propose that, in fact, there is no contradiction here, but rather a new piece added to the puzzle. In earlier work (Friedmann, et al. 2009), we proposed that the difficulty in the comprehension and production of object A-bar dependencies cannot be characterized as a problem with the A-bar movement or a problem with the object dependency per se but rather the problem resides in intervention locality considerations: the difficulty arises in configurations in which a lexically-restricted (object) DP moves across another lexically-restricted (subject) DP, an intervention configuration problematic for children, a difficulty captured by the featural Relativized Minimality approach (Friedmann et al. 2009; building on Rizzi 1990; 2004; Starke 2001).

And indeed, a further analysis of the spontaneous speech samples points exactly in this direction: the children produced many A-bar structures, including subject and object relatives, topicalizations, and Wh questions, and from age 3;3 all of them did, but none of the relatives, topicalizations, and Wh questions in the samples included an intervention structure of the relevant type, with a lexically-restricted DP crossing another one.

Instead, all the object dependencies that the children produced were structures without intervention. The object relatives they produced included a pronominal intervening subject, in the form of an arbitrary plural null subject (example (17)), or a referential (null/overt) subject pronoun (examples (18) and (19) respectively). Children also produced free object relatives at this stage (9 of the 14 children who produced object relatives).

For Wh questions, intervention occurs when the Wh element is of the which type, and hence, lexically-restricted, and the subject is also lexically-restricted. The object questions that appeared in the samples were mostly who/what questions, and the few which object questions included a pronominal (null or overt) subject (example 20) (many other utterances included which, but in a simple which-NP structure, like “which orange?”).

Crucially, none of the sentences with object dependencies that the participants produced included a lexically-restricted DP crossing another lexically-restricted DP.

Is it the case that children simply do not use two lexically-restricted noun phrases in the same clause, irrespective of the structure? Well, no. That this is not the case can be shown by the fact that 12 of the 20 children who produced subject relatives did so with a lexically restricted relative head and a lexically restricted object, hence with two lexically restricted DPs but not in an intervention configuration (see example (21). For a similar result in Italian see Martini et al. (2018).

Is it the case that children avoid lexically-restricted subjects? Again, no, in their simple SV sentences, 45 children produced lexically-restricted subjects.

The fact that we found object relative clauses, object questions, and topicalizations and no subject-object asymmetry is therefore fully consistent both with the Growing Trees approach and with the approach in terms of locality and intervention.

In fact, this points to another dimension of acquisition: acquisition is not just tree structure growing. Rather, we recognize here another developmental stage, which does not have to do with structure building but rather with the development of the ability to compute intervention configurations. The finding that children in our corpus did not spontaneously produce any intervention structure, even though they did produce so many object dependencies, lends strong support in favour of the intervention approach. It also supports the independence of this developmental dimension from structure building: the tree can be grown, and thus be able to host the relevant landing site positions of an A-bar dependency, but on top of it, the child has to be able to compute intervention locality.

4.6 An open question: Is there a stage earlier than Stage 1?

Stage 1 of the stages of acquisition of the syntactic tree we presented so far involved a tree consisting of both VP and IP. An open question is whether a stage exists that precedes this Stage 1, that includes an even smaller chunk of the syntactic tree. Three hypothetically possible stages preceding Stage 1 are imaginable. Below we describe each of them and address their hypothetical defining properties.²³

1. A pre-functional stage of bare VP without IP. One option for a pre-Stage 1 stage would be one in which only a bare VP is available, without the IP layer. Such a “pre-functional” stage, with no functional structure (as in Radford 1990; 1992; 1996), would allow the child to produce SV(O) sentences for transitives and unergatives. Predicting whether or not the child would be able to produce SV for unaccusatives would depend on the assumptions one holds with respect to the derivation of SV with unaccusatives: if the internal argument first moves to the edge of VP and then continues to spec IP, SV with unaccusatives would be possible as well. If, in contrast, movement from the internal argument position targets the spec IP directly, then presumably only the VS order would be available at this early stage for unaccusatives (possibly, with observable definiteness effects, given the early sensitivity to such effects: Belletti & Bianchi 2016; Belletti 2017).²⁴

   More straightforwardly, the hypothetical non-availability of the functional structure of the clause will also have implications for inflection: under the assumption that inflectional specifications such as, in particular, agreement with the subject in Phi features, and also tense inflection on the verb, require licensing of the inflected verb by the appropriate head(s) in the inflectional field, in a hypothetical stage without functional structure, the verb would not be properly inflected.

2. A stage of only lower functional layers above VP. Another option for an early stage preceding our Stage 1 is a stage in which VP is available, together with only lower functional layers (e.g., aspect but not tense in the Cinque 1999, hierarchy), but not including higher IP layers up to the position typically occupied by pre-verbal subjects in the adult system (i.e., Spec SubjP, as in Cardinaletti 2004; Rizzi 2006; Rizzi & Shlonsky 2007). In such a hypothetical stage, the verb would be only partially inflected (e.g., for Aspect, but not for Tense or Agreement. See Antinucci & Miller 1976; Salustri et al. 2004; see also Tsimpli 2005, for findings regarding Asp acquired before Tense). See Armon-Lotem 1997; 2008a where such an approach was developed in detail for the acquisition of Hebrew. Similar considerations as in a) above would apply for whether the child would be able to produce SV with unaccusatives.

3. A stage of structure without movement? A different type of possibility for a stage preceding our Stage 1 might be that the structure (VP+IP) is available but movement is not available yet. Internal and external Merge differ in the need of a preliminary search operation, which is only required in internal Merge. A hypothetically possible situation, then, would be that at an early stage, Merge is acquired but Search is not acquired yet. In this situation, structure building (external merge) will be available but movement (internal merge) will not. There could be a stage, then, in which children already have SVO for transitives, SV for unergatives, as these require structure building but no (explicitly visible) movement, but presumably only VS for unaccusatives, as SV with unaccusatives requires movement from the internal argument position to a higher spec position (with a result similar to a) and b) above). The non-availability of movement will also have implications for inflectional specifications on the verb, under the assumption that these are licensed through verb movement. In such a hypothetical stage without movement, the verb would most likely not be properly inflected.

In our data, we have not seen any of these hypothetical stages preceding Stage 1– none of the children showed the patterns expected under any of the three: we did not see a stage in which unaccusatives appeared only in VS order – there were no children who only produced unaccusatives in the VS order, without the SV order, contra possibility c) (and also, under certain assumptions of the movement of the internal argument, contra a) and b)).

Additionally, there is evidence that the agreement system is functioning, even for the children who were in the earliest stage of acquisition in our study, as we did not see children who made (number) agreement errors in SV sentences.²⁵ (and see Armon-Lotem & Berman 2003; Armon-Lotem (1997; 2006; 2008b) for an analysis of stages in the acquisition of agreement in early verbs in Hebrew). This means that the functional structure that is responsible for agreement is already in place in their syntactic trees. Under current assumptions, this implies the presence of the relevant functional structure for the checking of agreement and the ability to move there. Another independent indication for the availability of a functional structure at this stage comes from the children’s correct production of object case marking. This is evinced in the finding that all 23 children who were at Stage 1 produced the accusative case marker ‘et’ correctly before the definite object when they repeated simple SVO sentences. (In the samples from natural productions children at Stage 1 produced too few definite objects to allow for analysis of case markers’ production).

In conclusion, we did not see in our study any of the hypothetical stages considered in this section for a lower chunk of the tree acquired before Stage 1. This does not necessarily mean they do not exist, as it could be the case that the transition to the next stage is so short that our corpus study could not catch them (Radford 1996). It is fair to conclude, though, that we did not find any evidence supporting them.

5.1 Dialogue: Cartography providing a framework for the description of stages in acquisition

The cartographic representation of the left periphery offers a natural structural basis to understand the stage-by-stage development of syntactic structures.

The functional structure is ordered according to a sequence of functional heads. The key hypothesis here is that the tree grows in the child’s mind in the sense that internal layers are mastered before more external ones, respecting the cartographic hierarchy. Children can produce a certain construction only when they master the relevant functional heads involved in it. As for the acquisition of various types of movement, in a probe-goal approach to movement (internal merge licensed by a probe-goal search operation), the availability of the probing head is essential for a certain type of movement to take place, so the typology of movement reduces (in part) to a structural typology. Therefore, constructions involving functional heads in higher zones and types of movement targeting the higher zones are acquired later depending on the maturational stage of the child.

Stage 1: The first stage we have identified is a stage in which VP+IP are acquired. In this stage, both External and Internal Merge are available but only IP-internal movement is attested (A-movement to subject position, straightforwardly visible with unaccusative verbs). At this stage we also observe agreement licensed by functional structure, and SV structures with unergatives and transitives (and nonfinite complements of verbs, footnote 15). No left peripheral position appears to be active in this stage, and no movements that require these positions.

Stage 2: In the second stage, the lower field of the left periphery has become available. Cartographic analysis shows that the Q position is in this lower zone (lower than the topic position, the Int position, and the landing site of relative operators). So, Wh movement to the Q position is acquired, and root questions are found in this stage, as well as root yes/no questions (which presumably involve an operator in Q). The position of Mod, another functional head in the lower LP zone, also becomes available at this stage, allowing for the production of sentences with preposed adverbs. Whereas Wh questions are found in this stage, why questions are not found yet: this follows from the cartographic observation that why is hosted in the Spec of the dedicated left peripheral head, Int, higher than Q (Rizzi 2001). Embedded Wh questions, and full clausal subordination in general, are also not found in the second stage. This follows from the fact that full clausal subordination requires a fully developed C-system, projecting up to Force, the head that expresses the clause type (declarative, interrogative, exclamative, etc., see Cheng 1997; Zanuttini & Portner 2003) and is selected by higher selectors. Because the selected head, Force, is not available, full clausal subordination is not possible. A-bar constructions such as relative clauses and topicalization are not available yet at this stage, as the higher zone of the left periphery involving their landing sites is not accessible.

Stage 3: In the third stage, the structure of the higher LP becomes available, so that the whole cartographic structure of the C-system becomes accessible to the child. Selection from a higher predicate becomes possible, as the Force head is now available. Therefore, we observe full clausal subordination, so that children at this stage produce embedded declaratives, embedded Wh questions (both subject and object, as well as adjunct questions), and embedded yes/no questions, all selected by a higher predicate. Topicalization becomes available because the Top head is specified in the higher C-zone. Because the relevant landing site for relative clauses in the left periphery is now present, subject- and object relative clauses are also acquired in this stage. Why questions also become available, as the crucial head, Int, is specified in the higher CP zone.

Of course, the hierarchical information provided by cartographic analysis can only offer a partial guidance to the sequence of events in development, and interacts with orthogonal factors of complexity. So, for instance, in order to deal with certain intervention configurations in which the moved element and the intervener are both lexically-restricted (such as certain object relatives and certain object which questions), the availability of the structural position of the landing site in the cartographic representation is not enough, and it requires also the capacity to compute certain intervention configurations (the capacity to compute featural inclusion in the system of Friedmann et al. 2009; Belletti et al. 2012).²⁶ Therefore, stages in which these capacities are acquired may follow the completion of the acquisition of the syntactic structure, namely, they may follow Stage 3. When the capacity for computing intervention configurations is acquired, children become able to deal with configurations in which a lexically-restricted DP can be A-bar moved across another lexically-restricted DP.²⁷ So, as it should be expected, a comprehensive picture of developmental effects in the acquisition of syntactic constructions can only be provided by a multiplicity of factors, with the structural hierarchy interacting with independent factors of computational complexity. In this paper we have focused on the structural hierarchy, proposing that the structural sequences uncovered by cartographic research can offer a fruitful explanatory key in understanding the developmental sequence of events in the acquisition of syntax.

Due to its grammatical nature, our account predicts that, all things being equal, the same stages documented here on the basis of production data should also hold for comprehension, since grammar is directly implicated in both. It will be interesting yet challenging to test in the future the comprehension of the different structures investigated and see whether they also form a parallel Guttman scale, and whether the stages identified in production co-occur with stages in comprehension.

5.2 Dialogue: Patterns of acquisition informing syntactic theory regarding tree structure

Beside conforming to the cartographic order of functional heads, which we discussed above, the pattern of empirical findings emerging from the repetition test and the analysis of children’s spontaneous speech suggests novel insights into several theoretical issues concerning the shape of the syntactic tree.

5.3 Conclusion

Our study shows a fruitful dialogue between acquisition and syntactic mapping. We used cartographic insights as a detailed tool to understand the stage-by-stage unfolding of acquisition. Cartographic representations further allowed us to derive new predictions about acquisition that we then examined empirically. Reciprocally, data from development offered new evidence bearing on the cartographic organization, allowing us to adjudicate between alternative analytical hypotheses, and also raised new questions to further explore in the future.

Spontaneous speech corpus of 56 children

Our new analyses of the corpus of 56 children were done on the same corpus used in Friedmann & Reznick (this volume). The corpus included spontaneous speech samples of 56 children aged 1;6–6;1 (different from the children participating in the repetition task). The main criterion for selection of samples was that they will be large enough, so that they allow not only for the appearance of the structures that the child has already acquired, but also so it will be reasonable to conclude that if a certain structure did not appear in the sample, the child probably has not acquired it yet. The children who were 2;5 and older had an average of 151 utterances per sample (SD = 37); Some of the youngest children, aged 1;6–2;3, produced fewer utterances. So only samples in which the children had enough opportunity to produce utterances were included: sample with 50 clauses or less were included in the analysis only if they resulted from interactions that involved at least 100 turns. The average number of turns in samples with 50 clauses or less was 148. For the sake of comparability of the samples, we also limited the size of the samples that had more utterances to the first 200 utterances. The total number of utterances in the 56 samples was 6400. We analysed, for each sample, whether a list of structures appeared at least once in the sample. The examination of order of acquisition within the corpus relied on a corpus wide analysis of the appearance of structures: if structure A appeared either alone or with structure B, but structure B did not appear in samples without structure A, we concluded that structure A was acquired before structure B.

Longitudinal corpus of nine children

In the longitudinal data we could examine the order of acquisition of various structures for each child, by analysing the relative timeline of acquisition of the various structures between children. To examine the patterns of acquisition within a single child, we analysed the spontaneous speech of nine children who were recorded several times. In Section 4.4 we selected for the general analysis the two children for whom the database is the richest: Hagar and Leor. Hagar was recorded 114 times between the ages of 1;7–2;11, with an average of 219 utterances per sample. Leor was recorded 79 times between 1;9–3;0, with an average of 297 utterances per sample. The total number of utterances analysed for these children was 16,002.

In the analysis of yes/no questions compared to Wh questions in the longitudinal corpora we analyzed the corpora of 9 children: Hagar and Leor (described above), Lior, Naama, Smadar (the other three children reported in Friedmann & Reznick, this volume), and 4 additional children who had somewhat fewer samples, but still enough to time the acquisition of questions (Sivan, Ruthy, Hamutal, Asaf from Ravid 2004), with 9–20 samplings and 971–3005 utterances, added here courtesy of Julia Reznick.