Lexical and Semantic Development

Lexical and semantic development describes how children build their vocabulary (lexis) and learn the meanings (semantics) of words. From the first tentative words around age 12 months to the vocabulary explosion that follows, lexical development is one of the most visible and dramatic aspects of language acquisition.

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First Words and the Holophrastic Stage

Children typically produce their first recognisable words around 12 months of age, though there is considerable individual variation (some children produce words as early as 9 months, others not until 18 months).

The period from roughly 12–18 months is known as the holophrastic stage — children use single words to convey the meaning of an entire sentence.

Key Definition: Holophrastic stage — the period (approximately 12–18 months) in which children use single words (holophrases) to express complex meanings that would require a whole sentence in adult language. For example, "milk" might mean "I want some milk" or "I've spilled the milk", depending on context.

Examples of Holophrases

Holophrase	Possible Meanings (depending on context)
"Milk"	"I want milk" / "That is milk" / "I've spilled the milk"
"Daddy"	"Daddy is here" / "Where is Daddy?" / "That is Daddy's"
"Up"	"Pick me up" / "I want to go up" / "Look up there"
"No"	"I don't want that" / "That is wrong" / "Don't do that"

The meaning of a holophrase depends heavily on context, intonation, and gesture. Caregivers typically interpret holophrases by using these contextual clues.

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Nelson's First Word Categories

Katherine Nelson (1973) studied the first 50 words of 18 children and identified several important categories:

Category	Percentage	Examples
Naming/nominals (general)	51%	dog, ball, car, milk, shoe
Naming/nominals (specific)	14%	Mummy, Daddy, Rover
Action words	14%	go, up, sit, give
Modifiers	9%	big, hot, mine, nice
Personal-social	8%	no, yes, please, bye-bye
Function words	4%	for, is, what

Nelson found that the majority of children's first words are nouns — particularly names for people, animals, food, and objects. This is often called the noun bias. However, Nelson also noted individual differences:

• Referential children — tend to acquire a high proportion of nouns and use language primarily to name and categorise objects
• Expressive children — tend to acquire more social and personal words, using language primarily for interaction and emotional expression

Key Definition: Noun bias — the observation (Nelson, 1973) that children's earliest vocabularies are dominated by nouns, particularly names for concrete objects, people, and animals. This may reflect cognitive salience — objects are easier to categorise and point to than actions or abstract concepts.

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Overextension and Underextension

As children learn new words, they often make systematic errors in applying word meanings:

Overextension

Overextension occurs when a child uses a word too broadly — applying it to a wider range of referents than an adult would.

Rescorla (1980) identified three types of overextension:

Type	Description	Example
Categorical	Extending a word to other members of a similar category	Calling all four-legged animals "dog"
Analogical	Extending a word based on perceptual similarity	Calling a round ball "moon"
Relational	Extending a word based on a relationship or association	Saying "hat" while pointing at a head

Overextension is extremely common in children aged 1–2.5 years and typically involves about one-third of children's early words. It usually resolves as the child's vocabulary grows and they can make finer distinctions.

Key Definition: Overextension — the use of a word to refer to a broader category than its conventional adult meaning. For example, a child might call all men "Daddy" or all round objects "ball". This reflects the child's developing semantic categories.

Underextension

Underextension is the opposite — a child uses a word too narrowly, applying it to only a subset of its correct referents.

Example	Explanation
Using "cat" only for the family's cat, not for any other cats	The word is restricted to a single referent
Using "shoe" only for their own shoes	The word is applied too narrowly
Using "car" only for the family's car	The child has not generalised the concept

Underextension is thought to be more common than overextension in children's comprehension (what they understand), while overextension is more visible in their production (what they say). Underextension tends to attract less research attention because it is harder to observe — you notice when a child calls a horse a "dog", but you may not notice when they fail to call an unfamiliar cat a "cat".

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Eve Clark's Semantic Feature Theory

Eve Clark (1973) proposed the semantic feature theory to explain overextension. According to this theory:

• Word meanings consist of a set of semantic features (e.g. four legs, fur, moves, barks)
• Children initially learn only a few features of a word's meaning
• As they learn more features, their use of the word becomes more precise