A preschool teacher recorded a four-year-old child saying "I runned fast,"…

Concept: Overgeneralization (also called overregularization) is a well-documented stage in child grammatical development. Once a child extracts a productive rule from the language they hear — such as the pattern of attaching a tense-marking morpheme to a verb stem — the child begins applying that rule broadly across verbs in the same category, including verbs whose past-tense form is actually irregular and does not follow the rule.

Application: Here, the child produces "runned" by attaching the regular past-tense morpheme "-ed" to the irregular verb "run," a form no adult models. At the same time, the same child correctly produces "brought," the irregular past tense of "bring." This combination — a systematic, rule-following error on one irregular verb alongside correct retrieval of another irregular form — is the signature of a child who has extracted a productive grammatical rule and is actively applying it, occasionally overextending it before learning the exceptions.

Contrast with the other options:

• Failure in selective memory retention would predict inconsistent or random loss of irregular forms across different verbs, not one uniform substitution pattern that follows the regular past-tense rule.

• Responding to positive reinforcement requires that a caregiver has modeled or rewarded the specific form being produced; "runned" is not a form caregivers use or reinforce.

• Imitating the way adults speak requires the child to have heard the exact form from an adult; adults do not say "runned," so direct imitation cannot generate it.

Result: The systematic, rule-following nature of the error — applied to a verb whose irregular exception the child has not yet learned — identifies this as the application of a productive morpheme rule.