Exposition lays out all the groundwork in a novel that the reader cannot experience directly. Description provides those images and sensations that can be sense or felt, completing a mental picture of the setting and the characters. Dialog helps shape character through verbal interaction, and informs the reader at the same time that it moves action forward. Exposition fills in the gaps left by relying on purely observable description and involves the reader more intimately with the source material. Properly employed exposition addresses history, functionality, or purpose with information the reader needs but cannot witness or easily deduce. It may be presented in dialog, descriptively, or in narrative passages.