1 1/2 years to 2 years--Anticipatory Language, and the Holophrastic sentence.
A subtle change that takes place by in the second six months (1 1/2 to 2 years) is the generation of the word before the stimulus appears.
This is called Anticipatory Language and it takes speech out of the realm of the old stimulus-response paradigm. Now speech gives the baby some control over his/her environment.
For example, the baby says, "dada" and daddy appears. She says "baba," and someone gives her a bottle. This was the level of language that Itard longed to achieve for Victor the wild child. Unfortunately with the exception of perhaps only one instance in the visual modality, this goal was not achieved. On at least one occasion, Victor did spell out the work "milk," when he was thirsty.
The Holophrastic Sentence. The words that the child is generating during this period are more than simple referent-symbol relationships.