By age four, the child can respond to multi-word utterances with two or more related or unrelated objects and actions, as well as prepositional phrases and plurals. Skills in the area of social interaction also develop from birth. By age four, the child maintains extended conversations and varies his language content, form, and politeness depending on the listener's status as a peer, subordinate, or authority figure. The rate at which expressive language develops varies greatly from child to child. Initial use of gestures as intentional communication signals typically begins by age 15 months.
Consistency is noted in the child's correct production of vowel and lip closure sounds as well.
The four-year old child combines two or more sentences in using conjunctions and embedding. Spontaneous sentences contain complex modifications, such as infinitives, articles, third person verbs, past tense auxiliaries, and negated auxiliary verbs. By five years of age, the child forms complex sentences by combining three or more simple sentences. More complex verb phrase modifications are also evident, such as could, should, would and couldn't, wouldn't, shouldn't. The development of speech and language skills is dramatic during the first five years of a child's life.