Semantic development is more complex and slower than phonological or syntactical development and we keep expanding our semantic knowledge throughout our entire lives. The development of semantics involves two main activities: a constant expansion of vocabulary and a reorganisation of the semantic networks between words that constitute the semantic structure of language. Infants’ semantic development thus involves the gradual refinement of the meaning of words until their words approaches the composite of the adult meaning.
Although there is strong evidence that a child is predisposed to produce language, without the appropriate environment and social interaction the infant is not able to learn language. The first fifty words that infants utter reflect their immediate surroundings and include those objects that they interact with in their daily lives. By the age of three, infants may know up to a thousand words, and ten times as much by the age of six. But the exceptional growth of vocabulary does not imply that infants have grasped the semantic system of individual words.
Children initially use words in a restricted setting and their use of a particular word does not reflect the full capacity of the adult meaning because their semantic system is often incomplete. Words form part of a complex hierarchical network of associated meaning and children at their early stages of semantic development have not yet grasped the composite elements of lexical items.
Consequently, children during the one-word and two-word stages often display occurrences of overextension and underextension in their speech. Infants may use the word “fruit” to refer to an apple and are oblivious to the fact that the word refers to a whole category. Alternatively, they may extend the use of a particular word to refer to other objects that share a common feature such as shape, colour or size. For instance, a “ball” may be anything that has a round shape and is applied to an orange and to the moon.
During their gradual semantic development infants must acquire categorical concepts and move from gross undifferentiated categories to finer distinctions in meaning. These categorical concepts enable infants to extend their knowledge and make inferences on the appropriate use of a particular word. Adult speech also aids infants to categorise words in a useful way. Caregivers often label objects focusing on their salient features and correct overextension by explaining the rudimentary set of features pertaining to a particular word.