As children learn their mother tongues, they make systematic errors. For example, English-speaking children regularly say mouses rather than mice . Because children’s errors are not explicitly corrected, it has been argued that children could never learn to make the transition to adult language based on the evidence available to them, and thus that learning even simple aspects of grammar is logically impossible without recourse to innate, language-specific constraints. Here, we examine the role children’s expectations play in language learning and present a model of plural noun learning that generates a surprising prediction: at a given point in learning, exposure to regular plurals (e.g. rats ) can decrease children’s tendency to overregularize irregular plurals (e.g. mouses ). Intriguingly, the model predicts that the same exposure should have the opposite effect earlier in learning. Consistent with this, we show that testing memory for items with regular plural labels contributes to a decrease in irregular plural overregularization in six-year-olds, but to an increase in four-year-olds. Our model and results suggest that children’s overregularization errors both arise and resolve themselves as a consequence of the distribution of error in the linguistic environment, and that far from presenting a logical puzzle for learning, they are inevitable consequences of it.

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Words are often seen as the core representational units of language use, and the basic building blocks of language learning. Here, we provide novel empirical evidence for the role of multiword sequences in language learning by showing that, like words, multiword phrases show age-of-acquisition (AoA) effects. Words that are acquired earlier in childhood show processing advantages in adults on a variety of tasks. AoA effects highlight the role of words in the developing language system and illustrate the lasting impact of early-learned material on adult processing. Here, we show that such effects are not limited to single words: multiword phrases that are learned earlier in childhood are also easier to process in adulthood. In two reaction time studies, we show that adults respond faster to early-acquired phrases (categorized using corpus measures and subjective ratings) compared to later-acquired ones. The effect is not reducible to adult frequencies, plausibility, or lexical AoA. Like words, early-acquired phrases enjoy a privileged status in the adult language system. These findings further highlight the parallels between words and larger patterns, demonstrate the role of multiword units in learning, and provide novel support for models of language where units of varying sizes serve as building blocks for language.

This preregistered study tested three theoretical proposals for how children form productive yet restricted linguistic generalizations, avoiding errors such as *The clown laughed the man , across three age groups (5–6 years, 9–10 years, adults) and five languages (English, Japanese, Hindi, Hebrew and K'iche'). Participants rated, on a five-point scale, correct and ungrammatical sentences describing events of causation (e.g., *Someone laughed the man; Someone made the man laugh ; Someone broke the truck ; ?Someone made the truck break ). The verb-semantics hypothesis predicts that, for all languages, by-verb differences in acceptability ratings will be predicted by the extent to which the causing and caused event (e.g., amusing and laughing) merge conceptually into a single event (as rated by separate groups of adult participants). The entrenchment and preemption hypotheses predict, for all languages, that by-verb differences in acceptability ratings will be predicted by, respectively, the verb's relative overall frequency, and frequency in nearly-synonymous constructions (e.g., X made Y laugh for *Someone laughed the man ). Analysis using mixed effects models revealed that entrenchment/preemption effects (which could not be distinguished due to collinearity) were observed for all age groups and all languages except K'iche', which suffered from a thin corpus and showed only preemption sporadically. All languages showed effects of event-merge semantics, except K'iche' which showed only effects of supplementary semantic predictors. We end by presenting a computational model which successfully simulates this pattern of results in a single discriminative-learning mechanism, achieving by-verb correlations of around r = 0.75 with human judgment data.