How children understand the structure of words (morphology)

Child Language: How Children Understand the Structure of Words (Morphology)

Welcome to your revision guide for Morphology in Child Language Acquisition! If you are preparing for Component 2: Child Language (9EN0/02) of your Pearson Edexcel A Level English Language exam, this topic is essential. Don't worry if linguistic terminology feels overwhelming at first — we will break everything down into clear, bite-sized pieces with practical examples you can use directly in your exam essays.

1. The Basics: What is Morphology?

Morphology is the study of word formation and the internal structure of words. While syntax deals with the order of words in a sentence, morphology looks inside the words themselves to see how smaller building blocks combine to create meaning.

The core building block of morphology is the morpheme. A morpheme is defined as the smallest unit of grammatical or lexical meaning. Words can be made up of one or more morphemes.

Types of Morphemes

Morphemes are divided into two main categories:

• Free Morphemes: Morphemes that can stand completely on their own as independent words. They carry core lexical meaning.
Examples: dog, run, play, happy.

• Bound Morphemes: Units of meaning that cannot stand alone as words. They must be attached (bound) to a free morpheme to make sense.

Inflectional vs Derivational Morphemes

Bound morphemes perform two distinct jobs:

1. Inflectional Morphemes: These are grammatical markers added to a word that change its tense, number, or possession, but do not change the core word class.
Examples: Adding plural -s to dog creates dogs (both are nouns). Adding past tense -ed to play creates played (both are verbs).

2. Derivational Morphemes: These are prefixes or suffixes that significantly alter the meaning or change the word class of the root word.
Examples: Adding -ness to the adjective happy creates the noun happiness.

Key Takeaway: When analyzing child speech, check whether the child is using base words on their own (free morphemes) or successfully attaching grammatical endings (bound inflectional morphemes).

2. Measuring Growth: Mean Length of Utterance (MLU)

In your exam, you will be given transcripts of children speaking. To evaluate a child's morphological and grammatical complexity objectively, linguists calculate the Mean Length of Utterance (MLU).

The MLU Formula

\(\text{MLU} = \frac{\text{Total Number of Morphemes}}{\text{Total Number of Utterances}}\)

How to Count Morphemes in an Utterance

• "I play" = 2 morphemes (I [1] + play [1])
• "I played" = 3 morphemes (I [1] + play [1] + -ed [1])
• "Two dogs" = 3 morphemes (Two [1] + dog [1] + -s [1])

Analogy to remember: Think of morphemes like individual Lego bricks. A child who says "I played" is building a tower with 3 bricks, whereas "I play" only uses 2 bricks. A higher MLU score shows that the child is using more complex grammatical building blocks.

3. Roger Brown's Stages of Morphological Development (1973)

Linguist Roger Brown (1973) tracked young children and discovered that they acquire bound grammatical morphemes in a remarkably predictable order.

Brown's Developmental Stages

• Stage I (MLU 1.0–2.0): The child relies primarily on single words and early two-word combinations without grammatical inflections.
• Stage II (MLU 2.0–2.5): Bound morphemes begin to emerge (such as the present progressive -ing and regular plural -s).
• Stage III (MLU 2.5–3.0): The child starts using irregular past tense forms and possessive markers.

Acquisition Timeline of Key Morphemes

Brown identified 14 key grammatical morphemes. The earliest acquired morphemes include:

1. Present progressive (-ing): Typically acquired between 19–28 months (e.g., "going", "running").
2. Prepositions (in, on): Typically acquired between 27–30 months (e.g., "in box", "on chair").
3. Plural regular (-s): Typically acquired between 24–33 months (e.g., "cats", "dogs").
4. Past irregular: Typically acquired between 25–46 months (e.g., "came", "went").
5. Possessive ('s): Typically acquired between 26–40 months (e.g., "mummy's").

Memory Trick: Remember I-P-P-P — Ing, Prepositions, Plurals, Past irregular. This helps you recall the earliest morphemes children grasp.

4. Experimental Evidence: Jean Berko Gleason & The Wug Test (1958)

How do we know children are not simply memorizing and imitating the exact words adults say? Linguist Jean Berko Gleason (1958) designed an ingenious experiment called The Wug Test to answer this question.

The Experiment

• Children were shown a drawing of an imaginary, cartoon creature and told: "This is a Wug."
• Then, a second identical creature was shown: "Now there is another one. There are two of them. There are two...?"
• The child was prompted to complete the sentence.

Findings and Significance

• 76% of 4–5 year olds and 91% of 1st graders correctly responded with "Wugs" by adding the plural -s inflection.
• Why this matters for your exam: Because "Wug" is a completely made-up pseudo-word, the children could never have heard it from an adult before. This proved that children do not just imitate; they internalize morphological rules and apply them productively to brand-new words.

5. Virtuous Errors and Overgeneralization

When analyzing transcripts, you will frequently spot children saying things like "I runned", "He goed", or "two mouses". In everyday conversation, people might call these "mistakes", but in A Level English Language, we analyze them scientifically.

• Virtuous Error / Overgeneralization: This occurs when a child applies a regular grammatical rule (such as adding -ed for past tense or -s for plural) to an irregular word.
• Examples:
  – "I runned" (applying the regular past tense -ed to the irregular verb run).
  – "Two mouses" (applying the regular plural -s to the irregular noun mouse).

Examiner Insight: Always emphasize that virtuous errors are clear evidence of cognitive progress. They demonstrate that the child has mastered the underlying morphological rule and is actively testing and applying it.

6. Common Exam Pitfalls (And How to Avoid Them)

Examiner reports for Component 2 highlight recurring pitfalls. Keep these points in mind when writing your answers:

• Confusing Morphology with Syntax: Do not confuse word structure with sentence structure. If a child adds -ed to a verb, analyze it under morphology. If a child changes word order (e.g., placing the subject after the verb), analyze it under syntax.

• Being Purely Descriptive: Avoid simply writing: "The child says 'goed' instead of 'went'."
Upgrade your analysis: "The child produces a virtuous error by overgeneralizing the regular past tense inflectional morpheme '-ed' to the irregular verb 'go'."

• Ignoring MLU: Don't just guess a child's stage. Reference the Mean Length of Utterance (MLU) and connect it to Brown's Stages to evaluate developmental maturity.

• Looking Only for Plurals: While plural -s is common, search the data for other features like the copula verb (e.g., "He is happy" vs omitting it: "He happy") or auxiliary verbs.

7. Quick Revision Checklist

[ ] Can you define a free morpheme vs a bound morpheme?
[ ] Can you explain the difference between inflectional and derivational morphemes?
[ ] Do you know the MLU formula and how to calculate morphemes in an utterance?
[ ] Can you outline Roger Brown's Stages I–III and the early acquired morphemes (present progressive -ing, prepositions, regular plural -s)?
[ ] Can you explain how Jean Berko Gleason's Wug Test (1958) proves productive rule application?
[ ] Can you identify a virtuous error / overgeneralization in unseen data and explain why it shows linguistic growth?