Consequently age does not give a good indication of the level of a child's linguistic development. This is measured by recording at least 100 consecutive utterances and counting the number of morphemes, content and grammatical, in each utterance. Many of the achievements of children during this stage demonstrate a remarkable degree of systematic rule following. Other examples are provided by negation and question formation. In negating sentences children pass through three stages in a completely regular sequence.
Children go about the business of language acquisition in a very orderly way.
It is an active and constructive process. This somewhat mitigates the gavagai problem. Last lecture I discussed the marked differences between speech and writing. When speech is directly addressed to children, however, virtually all of the sentences are fully formed and correct. Although adult speech addressed to children is typically more grammatically well formed, Pinker makes the important point that it is usually not grammatically simpler.