How do children learn which verbs can take “un-”?

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To achieve adult-like language competence, children must learn to extend verbs into structures they have not encountered while avoiding expressions that native speakers consider ungrammatical. For example, “un-” can be added to many verbs to express the reversal of an action, but not all: “roll” becomes “unroll,” whereas “unclose” is considered ungrammatical.

The study compared theoretical accounts of how children learn this distinction. Children aged 5–6 (N=18), children aged 9–10 (N=18), and adults (N=18) rated the acceptability of “un-” prefixed forms of 48 verbs, with the bare verb forms included as a control.

Across verbs, the acceptability of ungrammatical “un-” forms such as “unclose” was negatively correlated with both the frequency of the bare form and the frequency of alternative forms such as “open.” These findings supported the entrenchment and pre-emption hypotheses, respectively. Independent ratings of how closely the verbs matched semantic properties characteristic of a hypothesized semantic cryptotype for “un-” prefixation significantly and positively predicted acceptability in every age group.

The relative importance of each factor differed between attested and unattested “un-” forms and also varied with age. The researchers interpreted the findings in the context of a new hybrid account designed to incorporate entrenchment, pre-emption, and verb semantics.