What is overgeneralisation and why do children use it?

Overgeneralisation: applying a regular grammatical rule in an irregular situation Examples of overgeneralisation: "I runned", "he hitted", "you buyed"In the above examples, the suffix used to form the regular simple past tense, "-ed", has been applied to the stem of the irregular verbs "run", "hit" and "buy". Although these utterances are non-standard they can be used as evidence to support a child's innate ability for language acquisition. The child has demonstrated their understanding of the grammatical rule for regular past participle formation because it is unlikely that they have ever heard an adult using these constructions. It is perhaps more likely that they have used their previously acquired knowledge of past tense formation and are applying it in a new situation (perhaps using their LAD thus supporting Chomsky's theory of nativism).Overgeneralisations can therefore be used as proof that children do not simply learn language by repeating what they have heard from adults because they are able to produce utterances that they have never heard before. Whilst they are non-standard, they demonstrate a chid's deeper understanding of the grammar behind the utterance and their awareness of the need to manipulate their language to fit the context in which they are speaking.