Speakers can add complexity in another way, by combining two or more clauses into a single utterance. This allows for linking clauses through coordination (where neither clause is syntactically dependent on the other) or through subordination. In subordinate constructions, one clause (the subordinate clause) is embedded in the matrix or main clause. This embedding can take one of two main forms. In the first, the embedded clause fills one of the grammatical roles in the matrix clause and acts as the subject or object, for instance, of the matrix verb (e.g., That Tim arrived early shocked them, Nan invited them to go skiing, Bill thought that they had already eaten). This is a type of complementation. In the second, the embedded clause modifies one of the constituents of the matrix clause. It can modify a noun phrase, for instance, with a relative clause (e.g., The house that was covered with ivy stood back from the street), or modify a verb phrase with a temporal clause (e.g., Kate opened the door when she heard the cat outside). These modifications typically allow for more elaborate identifications of referents in conversation and for identifications of events as related in time (sequential or simultaneous, for instance), as related by cause and effect, or as related through contingency.
All these devices allow speakers to convey more complex information in a single utterance and to produce coherent sequences of utterances when, for instance, recounting an adventure, telling a joke, or explaining how a toy came to be broken. To get to this point, children must learn how to talk about the causal and temporal relations that can connect events. They must also learn how to structure information and decide what belongs in a main clause versus a subordinate clause and what should be said first versus later. How speakers package information affects how their addressees interpret what is said. Notice the different meanings conveyed by the following utterances:
Tom threw the stick before the dog ran away.
After Tom threw the stick, the dog ran away.
Tom threw the stick and the dog ran away.
Part of learning more complex forms and how to use them involves learning how to package the information to be conveyed.
Why use more complex forms like this? There appear to be at least three factors at work here in development.