Irregular Third-Person Singular
Irregular third-person singular forms (does, has) are the eleventh of Brown's 14 morphemes, mastered between 28 and 50 months.
At a glance
- Acquisition order
- #11 of 14 (Brown 1973)
- Symbol / form
- does/has
- Brown's stage
- V
- Typical age of mastery
- 28–50 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
Irregular third-person singular refers to the small set of high-frequency English verbs whose third-person singular present form is not formed by regular -s suffixation. Brown identified three: "does" (from "do"), "has" (from "have"), and "says" (from "say"). He treated them as a single morpheme in his 14 because they share the grammatical function of third-person singular agreement and reach mastery in roughly the same developmental window. The morpheme is interesting because the child must memorise each form as an item rather than applying a productive rule, which slows acquisition relative to the regular -s sibling.
Acquisition trajectory
Children begin producing "does" and "has" sporadically in late Stage IV, often as memorised whole-word lexical items embedded in fixed phrases ("she does it", "he has one"). Mastery in obligatory contexts is reached by approximately 50 months in typical development. The acquisition trajectory is item-by-item rather than rule-based, and individual children show wide variability in which irregular form is acquired first. Overgeneralisation of the regular pattern is the canonical error: "she haves", "he doos", which signals that the child has extracted the regular third-person rule but not yet sorted out which verbs are exceptions. The U-shaped pattern observed for irregular past tense is repeated here in miniature, but the developmental window is shorter and the recovery to adult-like use is faster. Children with DLD often produce neither the irregular form nor a regular overgeneralisation, instead defaulting to the bare stem ("she have", "he do").
Examples in obligatory context
These are the kinds of child utterances a clinician would code as a correct production of does/has when scoring a language sample.
- “She does the dishes.”
- “He has a cookie.”
- “She says hello.”
- “My dad does it.”
- “My sister has a doll.”
- “The cat has fur.”
Common errors during the acquisition window
- Overgeneralisation of regular -s: "she haves", "he doos"
- Bare stem in obligatory context: "she have", "he do"
- Substitution of the wrong irregular: "she haves" for "she has"
- Omission of the verb entirely in a fixed phrase: "she dishes" for "she does dishes"
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
Like its regular counterpart, irregular third-person singular is sensitive to childhood DLD. The diagnostic pattern is bare-stem use in obligatory contexts ("she have", "he do") rather than overgeneralisation, which is the typical error in unaffected peers. Because the irregular forms are high-frequency and repeated dozens of times in any classroom day, sustained bare-stem use into kindergarten is a stronger clinical signal than for many of the lower-frequency morphemes. Score irregular third-person singular in a language sample by identifying every obligatory context with "do", "have", or "say" inflected for third-person singular present and coding for correct production, bare stem, overgeneralisation, or omission.
“When a 5-year-old says "she have a cookie", that is not a slip — it is the exact same grammatical hole as "she walk to school yesterday". Score them as one tense-and-agreement composite.”
Get the full analysis
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Free tools for scoring this morpheme
MLU Calculator
Paste a language sample and get Mean Length of Utterance in morphemes and words, total utterances, total morphemes, and the matching Brown's stage. Implements Brown (1973) morpheme counting rules and runs entirely in your browser.
Open toolBrown's Stages Lookup
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.
Open toolDSS Calculator
Free Developmental Sentence Scoring (DSS) calculator for speech-language pathologists. Paste 50 sentences, tap weighted points across the eight Lee (1974) grammatical categories — Indefinite Pronouns, Personal Pronouns, Main Verbs, Secondary Verbs, Negatives, Conjunctions, Interrogative Reversals, Wh-Questions — plus the all-correct sentence point, and the calculator returns the live DSS with a per-category breakdown. Mobile-friendly tap-through grid, client-side, no sign-up.
Open toolRelated morphemes
Regular 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.
#9 · Stage IVRegular 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.
References
- Brown, R. (1973). A First Language: The Early Stages. Harvard University Press, pp. 254–271.
- Rice, M. L., Wexler, K., & Cleave, P. L. (1995). Specific language impairment as a period of extended optional infinitive. JSLHR, 38(4), 850–863.
- Marchman, V. A., & Bates, E. (1994). Continuity in lexical and morphological development: A test of the critical mass hypothesis. Journal of Child Language, 21(2), 339–366.