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Morpheme #12 of 14Brown's Stage V29–48 months

Uncontractible Auxiliary

Uncontractible auxiliary 'be' is the twelfth of Brown's 14 morphemes, mastered between 29 and 48 months in obligatory non-contractible contexts.

At a glance

Acquisition order
#12 of 14 (Brown 1973)
Symbol / form
is/are/was (auxiliary, uncontractible)
Brown's stage
V
Typical age of mastery
29–48 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

The auxiliary use of "be" combines with a present participle to form the present progressive ("she is running") or with a past participle to form the passive. Brown distinguished the auxiliary use from the copula use in his 14 because they reach mastery on different timelines, and he further distinguished uncontractible from contractible contexts for the same reason he split the copula. The uncontractible auxiliary appears in question fronting ("is he running?"), tag questions ("she is, isn't she?"), and emphatic constructions ("yes she is running") where the auxiliary cannot be reduced to a clitic.

Acquisition trajectory

Children produce auxiliary "be" sporadically in late Stage III, usually first as the contractible form ("he's running") and only later as the uncontractible form. Mastery in uncontractible contexts is reached by approximately 48 months in typical development. The acquisition lag relative to the copula is striking: a child can be using uncontractible copula "be" reliably ("there it is") for several months before producing uncontractible auxiliary "be" in question forms ("is he running?"). Brown attributed this to the syntactic complexity of fronting the auxiliary in question formation rather than to any deficiency in the verbal morphology. The error pattern is omission ("he running?", "they playing?") with rising intonation substituting for the missing auxiliary. Bilingual children whose other language has no auxiliary equivalent may show extended delay without the pattern signalling a disorder, and clinicians should interpret in dialectal context.

Examples in obligatory context

These are the kinds of child utterances a clinician would code as a correct production of is/are/was (auxiliary, uncontractible) when scoring a language sample.

  • “Is he running?”
  • “Are they coming?”
  • “Was she crying?”
  • “Yes I am.”
  • “The ball is rolling.”
  • “They were playing outside.”

Common errors during the acquisition window

  • Omission in question form: "he running?" for "is he running?"
  • Substitution of bare stem: "he be running"
  • Failure to invert the auxiliary in questions: "he is running?" for "is he running?"
  • Persistent omission in obligatory tag-question contexts

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

Uncontractible auxiliary is highly sensitive to DLD because it sits at the intersection of tense marking and syntactic complexity. The optional-infinitive profile predicts prolonged omission of auxiliary "be" in obligatory contexts, and the question-fronting requirement adds a syntactic load that the copula does not. Children with DLD frequently produce question forms with rising intonation rather than auxiliary inversion ("he running?") well into kindergarten. Score uncontractible auxiliary in a language sample by identifying every obligatory question and tag-question context where the auxiliary must surface and coding each as correct, omitted, or substituted. Pair the score with uncontractible copula and contractible auxiliary for a complete picture of "be" verb development.

“Question forms tell you more about a child's grammar than declaratives. Get five minutes of yes-no questioning in your sample and the auxiliary system reveals itself.”
Questions surface the auxiliary

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.

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Brown'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.

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DSS 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.

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Related morphemes

#7 · Stage III

Uncontractible Copula

Uncontractible copula 'be' is the seventh of Brown's 14 morphemes, mastered between 27 and 39 months in obligatory non-contractible contexts.

#13 · Stage V+

Contractible Copula

Contractible copula 'be' is the thirteenth of Brown's 14 morphemes, mastered between 29 and 49 months in obligatory contractible contexts.

#14 · Stage V+

Contractible Auxiliary

Contractible auxiliary 'be' is the fourteenth and last of Brown's 14 morphemes, mastered between 30 and 50 months and the last to reach criterion.

References

  1. Brown, R. (1973). A First Language: The Early Stages. Harvard University Press, pp. 337–367.
  2. Cleave, P. L., & Rice, M. L. (1997). An examination of the morpheme BE in children with specific language impairment: The role of contractibility and grammatical form class. JSLHR, 40(3), 480–492.
  3. Rice, M. L., & Wexler, K. (1996). Toward tense as a clinical marker of specific language impairment in English-speaking children. JSLHR, 39(6), 1239–1257.