'The cat is washing herself'


The structural rules we use to combine words into sentences.
The words within a sentence need to be put together in the correct order and relations to other words in the sentence to convey the intended meaning. For example, when making a sentence into a question we change the order of the words around. Therefore a sentence that is asking a question is different to a sentence that is not asking a question.
Here we can see how the order of the words is changed to make a sentence into a question. To change the words around we unconsciously use our grammatical knowledge - our syntax (i.e. rules to combine words into sentences).

Some children with language impairment have problems using syntax, and therefore the way they order words in a sentence may be incorrect. For example, a child with a language impairment might say 'Who did Marge see someone?' (the correct form would be 'Who did Marge see?'), whereas a typically developing child of the same age or younger would not make such mistakes.