Ann Peters and Dan Dinnsen are leaving our editorial team. Ann Peters has served as an Associate Editor for 8 years and Dan Dinnsen for 5 years. In both cases, their contribution to the Journal has been invaluable and on behalf of the Editorial Team, of those who submit papers to the Journal and of those who read it, I would like to thank them for their collegiality and for all their extremely careful and hard work.

Research undertaken to date suggests that important developments in the understanding and use of intonation may take place after the age of 5;0. The present study aims to provide a more comprehensive account of these developments. A specially designed battery of prosodic tasks was administered to four groups of thirty children, from London (U.K.), with mean ages of 5;6, 8;7, 10;10 and 13;9. The tasks tap comprehension and production of functional aspects of intonation, in four communicative areas: CHUNKING (i.e. prosodic phrasing), AFFECT, INTERACTION and FOCUS. Results indicate that there is considerable variability among children within each age band on most tasks. The ability to produce intonation functionally is largely established in five-year-olds, though some specific functional contrasts are not mastered until C.A. 8;7. Aspects of intonation comprehension continue to develop up to C.A. 10;10, correlating with measures of expressive and receptive language development.

The present study investigates the performance of 96 Cantonese-speaking three- to five-year-old preschoolers on three false belief tasks – a deceptive object, a change of location, and an unexpected contents task encompassing a variety of task factors. Most importantly, the research examines the possibility that false belief performance depends on specific linguistic factors such as the type of verb used in the test question – an explicitly false vs. a neutral belief verb. Cantonese was chosen as particularly useful for examining this question because it explicitly codes belief status as either neutral (nam5) or false (ji5wai4), and because it offers additional linguistic and cultural contrasts to research conducted on false belief with children learning English and other Indo-European languages. As expected, a strong age effect was found, as well as a significant advantage for children who received the explicit false belief (ji5wai4) wording and for those who were asked to explain rather than predict the protagonist's actions. Interestingly, there was also a strong task difference with children performing better on the deceptive object task than on the other two false belief tasks. We argue that these results point both to universal trajectories in theory of mind development and to interesting, but localized, effects of language and culture on children's false belief understanding.

The present article focused on two types of communicative intent (directing behaviour vs. eliciting talk) expressed by mothers and teenagers during everyday family interactions in Estonian, Finnish, and Swedish mono- and bicultural families. Three monocultural groups consisted of 17 Estonian, 19 Swedish, and 18 Finnish families living in their country of origin; two bicultural and bilingual groups consisted of 18 Estonian and 18 Finnish families residing in Sweden. All the children were between 9;0 and 13;0. The results revealed that the Estonian monocultural mothers were highly directive and direct: issuing behavioural directives most frequently and using the highest proportion of imperatives among all samples. Contrary to our expectations, the mothers who tended to be more concerned with controlling their children's behaviour also elicited conversation more frequently from teenagers by using a larger number of information requests. These requests seemed to serve as another form of attempted control over adolescents' behaviour – their communicative behaviour. The Swedish monocultural children were more active in controlling their mothers' behaviour than their counterparts, possibly illustrating the Swedish value of generational equality.

In a longitudinal study, 17 parent–child dyads were observed during free-play when the children were 1;0, 1;6, and 2;0. Parents' labelling input in the verbal and gestural modalities was coded at each session, and parents completed a vocabulary checklist for their children at each visit. We analysed how the frequency of labelling in the verbal and gestural modalities changed across observation points and how changes in parental input related to children's vocabulary development. As a group, parents' verbal labelling remained constant across sessions, but gestural labelling declined at 2;0. However, there are notable individual differences in parental trajectories in both modalities. Parents whose verbal labelling frequency increased over time had children whose vocabulary grew more slowly than those whose labelling frequency decreased, remained constant, or peaked at 1;6. There were few systematic relations between patterns of parental gesturing and children's vocabulary development. Parents' verbal and gestural labelling patterns also appeared dissociable. However, parents' words and gestures were correlated when their children were 1;6, suggesting that gestures serve an important bootstrapping function at a critical point in children's vocabulary development.

Interactions between six toddlers (aged 1;0 to 1;6) and adults were examined to ascertain adult perceptions of toddler utterance relatedness and to determine temporal and interactional features that underlie those perceptions. Five raters made judgments regarding relatedness of the child utterances to the previous adult utterances; 251 utterances were examined. Utterances judged by adults as related occurred within 4·25 seconds of the preceding adult utterance nearly 90% of the time. This study also points to the need for using interactional categories that go beyond describing utterance relatedness, and introduces terms (i.e. co-participatory, initiation, narrowed focus) for doing so.

We explored vocabulary competence in 55 firstborn and secondborn sibling pairs when each child reached 1;8 using multiple measures of maternal report, child speech, and experimenter assessment. Measures from each of the three sources were interrelated. Firstborns' vocabulary competence exceeded secondborns' only in maternal reports, not in child speech or in experimenter assessments. Firstborn girls outperformed boys on all vocabulary competence measures, and secondborn girls outperformed boys on most measures. Vocabulary competence was independent of the gender composition and, generally, of the age difference in sibling pairs. Vocabulary competence in firstborns and secondborns was only weakly related.

Many researchers believe that there is a logical problem at the centre of language acquisition theory. According to this analysis, the input to the learner is too inconsistent and incomplete to determine the acquisition of grammar. Moreover, when corrective feedback is provided, children tend to ignore it. As a result, language learning must rely on additional constraints from universal grammar. To solve this logical problem, theorists have proposed a series of constraints and parameterizations on the form of universal grammar. Plausible alternatives to these constraints include: conservatism, item-based learning, indirect negative evidence, competition, cue construction, and monitoring. Careful analysis of child language corpora has cast doubt on claims regarding the absence of positive exemplars. Using demonstrably available positive data, simple learning procedures can be formulated for each of the syntactic structures that have traditionally motivated invocation of the logical problem. Within the perspective of emergentist theory (MacWhinney, 2001), the operation of a set of mutually supportive processes is viewed as providing multiple buffering for developmental outcomes. However, the fact that some syntactic structures are more difficult to learn than others can be used to highlight areas of intense grammatical competition and processing load.

MacWhinney's stimulating discussion suggests that there are many lines of argument that may address concerns raised by theorists who are concerned that there is a logical problem of language acquisition. This commentary argues: (1) that if the ‘logical problem’ applied to language, it would apply, with curious consequences to any learning by experience; (2) that the logical problem does not apply – given sufficient positive data from any reasonable language, language can be learned, in a probabilistic sense, by an ‘ideal learner’ using a simplicity principle; and (3) that a simplicity, or minimum description length, principle may provide a useful methodology for assessing claims concerning learnability of particular linguistic structures.

The outcome of scientific research depends on how a phenomenon is viewed and how the questions are phrased. This applies also to the nativist view of language acquisition. As a complement to MacWhinney's discussion of nativism from the viewpoint of cognitive psychology, I would like to devote this commentary to the question of the title from the viewpoint of computational linguistics.

MacWhinney argues that the logical problem of language acquisition is no longer. It was a problem back in the 1970s when the guiding premises of the field were that language structure is highly abstract, that the child's input is a poor source of information about grammar, and that the child's learning mechanisms are inadequate to bridge the gap between the input the child receives and the grammar the child acquires. Now, however, we have new linguistic theories which show that language structure is not abstract but arises from cognition, and we have evidence that input is a rich source of information, and we have reason to believe that the child has a powerful array of learning procedures at his or her disposal. The gap between input and acquisition thought to exist in the 1970s has been closed, and thus, MacWhinney argues, there is no need to attribute innate linguistic knowledge to the child.

For over 35 years, beliefs about the learnability of natural language have acted as roadblocks in the way of further development in linguistics. Rigorous and useful formal work has led to the unwarranted adoption of extreme positions which in turn have tended to stifle collaboration and polarize debate. In his article, MacWhinney suggests a way around such roadblocks – or rather many ways around. He demonstrates that we should look for multiple mechanisms to help understand how it is that children learn language from the evidence to which they are exposed.

It would seem to be incomplete for any introduction to language acquisition to leave the ‘logical problem of language acquisition’ untouched – in fact, it would seem to be logical to just start the introduction with the logical problem. MacWhinney lays out a proposal here that attempts to dismantle the logical structure of the logical problem: there is no logical problem, if we consider carefully (a) the actual input that children receive from parents, and (b) the mechanisms that children use to handle possible pitfalls in extracting grammar from the input.

MacWhinney's list of proposed mechanisms for language acquisition seems so all-encompassing that it might appear churlish to dwell on a mechanism that's left out, but on his ultimate list of critical mechanisms there is an indeed an important (and intended) omission: innate, linguistically-specialized constraints. Such constraints are indeed mentioned, but if I understand the point of the article correctly, it is to argue that seven cognitive mechanisms, ranging from competition to cue construction, indirect negative evidence and monitoring, collectively obviate the need for any innate machinery that it specialized for language. Why not include room for innate, domain-specific constraints, too?

MacWhinney (2004) has provided a clear and welcome synthesis of many strands of the recent research addressing the logical problem of first language acquisition from a non-nativist or non-generative grammar framework. The strand that I will comment on is the one MacWhinney calls the ‘pivot’ of his proposal, namely, that acquiring a grammar is primarily a function of learning ITEM-BASEDPATTERNS (e.g. pp. 23–29, 41, passim). These item-based patterns serve a number of dominant roles within MacWhinney's proposal, including enforcing children's conservatism (thereby reducing greatly their overgeneralizations and need to recover from the same), supporting the probabilistic nature of grammar, and enabling the competition that promotes recovery from the overgeneralizations that do occur. My concern here is primarily with the first role, that of enforcing children's conservatism, and especially with the exclusive use of language PRODUCTION as the demonstrated support of this conservatism.

The central question posed by the so called ‘logical problem of language acquisition’ is how it comes to be that children are able to GENERALIZE from a finite set of linguistic data to acquire (learn, develop, grow) a computational system (grammar) that applies to novel examples not encountered before. The difficulty of this generalization problem was first posed cogently by Gold and while Macwhinney discusses the Gold framework and the linguistic literature on this matter, it is worth noting that the Gold framework is not the only one. There are at least two important new sources of insight from computational learning theory in the decades following Gold that need to be kept in mind. First, there is the development of empirical process theory that forms the basis of any analysis of statistical learning (see summary in Vapnik, 1998). Applying this approach to language (see Niyogi, 1998 for a treatment), one concludes that the family of learnable grammars must have a finite Vapnik Chervonenkis (VC) dimension. The VC dimension is a combinatorial measure of the complexity of a class of functions. Grammars may be viewed as functions mapping sentences to their grammaticality value. In this more sophisticated sense of the VC dimension, the class of grammars must be constrained. Second, there is the development of the theory of computational complexity suggesting that while a learning algorithm might exist, it may not be efficient, i.e. run in polynomial time. These two developments come together in the influential Probably Approximately Correct (PAC) model (Valiant, 1984).

MacWhinney's paper focuses on the role of input and learning strategies in explaining how language is acquired, essentially denying the poverty of stimulus assumption on which the so-called ‘logical problem of language acquisition’ is based.

MacWhinney is to be commended for reopening questions about the logical problem of language acquisition in the light of new data and models. Unfortunately his discussion is marred by technical errors, false dichotomies, and inadequate attention to detail.

I would like to begin by clarifying some technical points regarding learnability and Gold's theorem and will work my way around to advocating the power of distributed connectionist networks. I may wind up repeating much of what MacWhinney has already said, but I hope to do so in a manner that clarifies the status of and relationship between his seven solutions to the language acquisition problem.