The five stages of syntactic and morphological (communication) development are a framework created to help understand and support early language development in the English language. The framework describes the way the number of words/phrases that an individual uses slowly lead to the use of different grammatical structures that increase with difficulty.
Each stage is based on an individual’s mean length of utterance (MLU).
MLU is a widely used measure to look at how long an individual’s sentences are. As an individual’s MLU increases, this is often a sign that the individual is using more complex language.
To find out the MLU we take the number of words and morphemes (small parts of words that have meaning) and divide that by the number of phrases/sentences spoken.
For example: “I go play” (shorter MLU) versus “I am going to go and play with my Lego” (higher MLU).
The five stages of communication can be used as a guide to identify the communication stage of an AAC user. This will help to select words/phrases to use within an AAC system.
Stage One
MLU: 1.0-2.0 (can speak mostly single words and basic two-word phrases)
Age Range: 12 to 26 months
Structure of Words/Phrases: 50-60 basic words/phrases: Milk two| Doggy woof
Stage Two
MLU: 2.0-2.5 (can speak simple sentences and two to three words)
Age range: 27 to 30 months
Structure of Words/Phrases:
Present progressive: It’s working
In: In bin
On: On box
S plurals: My toys
Stage Three
MLU: 2.5-3.0 (can speak two to four words with more complexity)
Age range: 31 to 34 months
Structure of Words/Phrases:
Irregular past tense: Me ate fast
Possessive ending in S: Mummy’s book
Uncontractible copula: She was sad
Stage Four
MLU: 3.0-3.75 (can speak three to five words with more complexity)
Age range: 35 to 40 months
Structure of Words/Phrases:
Article: In the rubbish
Regular past tense verbs ending in ed: I screamed
Third person regular, present tense: She runs fast
Stage Five
MLU: 3.75-4.5 (can speak four to six words with increased complexity)
Age range: 41 to 46 + months
Structure of Words/Phrases:
Third person irregular: Daddy gives hugs
Uncontractible auxiliary: Mummy is smiling
Contractible copula: They’re tired
Contractible auxiliary: He’s playing
Bowen, C. (1998). Brown’s stages of syntactic and morphological development. https://www.speech-language-therapy.com/index.php?option=com_content&view=article&id=33:brown&catid=2:uncategorised&Itemid=117
Brown, R. (1973). A first language: the early stages. Harvard University Press.
Spencer, A. (2001). Morphology in linguistics. In N. J. Smelser & P. B. Baltes (Eds.), International encyclopedia of
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Tager-Flusberg, H. (2002). Language acquisition. In V. S. Ramachandran (Ed.), Encyclopedia of the human brain
(pp. 617-629). Academic press.