Underextension is a term used to describe the inability of a child to extend the meaning of a newly-learned word to the other objects within the same category. This term is mostly used in sociological and psychological studies to describe the process of development and acquisition of new skills by children.


All the children pass the specific stages as they grow up. One of the significant transformations relates to their speech development and acquisition of new words. This process includes some difficulties every child faces on the way. The most known issue is a child’s inability to assign a new concept to the category of objects, which it describes.

For example, a child learns the word “a car” when his parents give him a toy for his birthday. When he meets a car in the street while walking with his mother, he does not recognize the object and sees no similarities between the big object moving on the road and the toy in his hand. He starts asking his mother what the new thing is. Another example is a child who knows who “mama” is, but does not understand why other children use this word for one of their parents too.

Not only nouns but also verbs can lead to mistakes among children. If a child learns what the verb “sleep” means in relation to other people, he will not be able to apply it to a sleeping dog or cat. This type of underextension is less common but still happens in the learning process.

The third type of underextension applies to the words which appear in a specific context only instead of extending them to other situations. In this case, a child might use the word “light” only in relation to a table lamp or any other source of it instead of using this term in general.