Regular Plural -s
Regular plural -s is the fourth of Brown's 14 morphemes, marking countable noun plurality and reaching mastery between 27 and 33 months.
At a glance
- Acquisition order
- #4 of 14 (Brown 1973)
- Symbol / form
- -s
- Brown's stage
- II
- Typical age of mastery
- 27–33 months
Mastery is defined as correct use in 90% of obligatory contexts across three consecutive language samples (Brown 1973). Individual variation is wide — these ranges describe typically developing English-speaking children and should be cross-referenced against the primary literature before clinical use.
What this morpheme is
Regular plural -s is the bound suffix that marks the plural of countable nouns in English ("cats", "boxes", "puppies"). It has three phonological allomorphs — /s/, /z/, and /əz/ — and the child must control all three to be credited with mastery. Brown placed it fourth in his order because the regular plural reached criterion in the second half of Stage II, slightly after the locative prepositions. The morpheme is contrastive — its presence or absence changes the meaning of the noun phrase — which gives the child strong communicative motivation to mark it once the underlying grammatical concept is in place.
Acquisition trajectory
Children begin using regular plural -s sporadically in early Stage II, often on a small set of high-frequency nouns ("shoes", "cookies", "dogs"), and reach 90% mastery in obligatory contexts by approximately 33 months. The acquisition of the three allomorphs is staggered: voiceless /s/ after voiceless consonants comes earliest, voiced /z/ after voiced consonants and vowels comes shortly after, and the syllabic /əz/ after sibilants is the last to be mastered. Overgeneralisation is the canonical error — "foots", "mouses", "sheeps", "childs" — and it is a sign of healthy grammatical development rather than a problem. Brown observed that overgeneralisations actually increase in frequency for several months after the rule is established, then taper off as the child learns the irregular forms. Bilingual Spanish-English children may transfer Spanish plural marking and produce double-marked forms ("un cookies") in early acquisition; this is a typical interaction.
Examples in obligatory context
These are the kinds of child utterances a clinician would code as a correct production of -s when scoring a language sample.
- “Two cats.”
- “I have cookies.”
- “The dogs are running.”
- “My shoes are wet.”
- “Where are the books?”
- “Look at the trucks.”
Common errors during the acquisition window
- Overgeneralisation to irregular plurals: "foots", "mouses", "sheeps", "childs"
- Omission of plural -s on a known countable: "two cat" for "two cats"
- Failure to control the syllabic /əz/ allomorph: "two box" for "two boxes"
- Inconsistent application across the same noun in the same sample
Many of these errors are developmentally normal during the acquisition window. The clinical signal is persistence past the typical age of mastery, not the presence of any single error in early production.
Clinical relevance and scoring
Regular plural -s is one of the more sensitive morphemes for distinguishing typical development from DLD because the three allomorphs require both phonological and morphological control. A child who omits the syllabic /əz/ form ("two box") while producing /s/ and /z/ correctly is showing a phonological constraint, not a grammatical deficit, and the intervention target is different. By contrast, a child who omits all three allomorphs of plural -s while producing other Stage II morphemes is showing a grammatical pattern consistent with DLD. To score plural -s in a language sample, identify every obligatory context for a count-noun plural and code each as correct, omitted, or substituted. Mastery is 90% across the three allomorphs combined, per Brown.
“Plural overgeneralisations like "foots" and "mouses" are not errors to correct — they are evidence the child has acquired the rule. Document them in the report as a strength.”
Get the full analysis
Score -s automatically with ConductSpeech
Upload the audio. ConductSpeech transcribes the language sample, identifies every obligatory context for -s, computes the percentage correct, and writes a parent- and team-ready summary in minutes.
Free tools for scoring this morpheme
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Interactive reference for Brown's (1973) five stages of grammatical development. Look up a stage by child age or MLU, see the MLU range, acquired morphemes, example utterances, and clinical milestones for each stage.
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Open toolRelated morphemes
Regular Past -ed
Regular past tense -ed is the ninth of Brown's 14 morphemes, marking past on regular verbs and reaching mastery between 26 and 48 months.
#10 · Stage IVRegular Third-Person Singular -s
Regular third-person singular -s is the tenth of Brown's 14 morphemes, marking present-tense agreement and reaching mastery between 26 and 46 months.
#5 · Stage IIIrregular Past Tense
Irregular past-tense verbs ("went", "ate", "broke") are the fifth of Brown's 14 morphemes, mastered between 25 and 46 months in typical development.
References
- Brown, R. (1973). A First Language: The Early Stages. Harvard University Press, pp. 298–322.
- Berko, J. (1958). The child's learning of English morphology. Word, 14(2-3), 150–177.
- Marcus, G. F., Pinker, S., Ullman, M., Hollander, M., Rosen, T. J., & Xu, F. (1992). Overregularization in language acquisition. Monographs of the Society for Research in Child Development, 57(4), 1–182.