Harper Lee's To Kill A Mockingbird is written in the first-person perspective, and in the past tense. We can see this from the opening line of the novel: "When he was nearly thirteen, my brother Jem got his arm badly broken at the elbow." Because the story is narrated in the first person and in the past tense, its language is personal, reflective, and sometimes nostalgic.
An example of language which might be considered nostalgic can be found in chapter 4. Here, Scout, looking back retrospectively, says:
Summer was our best season: it was sleeping on the back screened porch in cots, or trying to sleep in the treehouse ... but most of all, summer was Dill.
Passages like this, in which an older Scout looks back fondly on innocent times from her childhood, are common throughout the text. Another example can be found in chapter 13, when Scout remembers with affection her relationship with her father:
I turned to go and met Atticus' vest front. I buried my head in it and listened to the small internal noises that went on behind the light blue cloth: his watch ticking, the faint crackle of his starched shirt, the soft sound of his breathing.
At times in the novel, Scout's language is also rather reflective, as the older Scout who narrates the story reflects on the lessons she learned when she was younger. For example, in the final chapter of the novel, Scout reflects that "Atticus was right...you never really know a man until you stand in his shoes and walk around in them." The ability to empathize with other people, and to thus not be too judgemental, is a lesson that Scout learns from her father throughout the course of the story.
Much of the story focuses on the exchanges between the three children—Scout, Jem, and Dill. The language of the story, especially in the parts which have lots of dialogue, is thus also characterized by the playful digressions and naivety one might expect from children. In the opening chapter, for example, Scout, Jem, and Dill are discussing how to make Boo Radley come out of his house. Jem, thinking aloud, says, "it's sort of like making a turtle come out ... Strike a match under him." Dill then asks, "How do you know a match don't hurt him?" Jem duly responds with, "Turtles can't feel, stupid." Insulted, Dill retorts, "Were you ever a turtle, huh?" These conversations are a huge part of the novel's charm. They also emphasize the innocence and naivety of the children and thus also, by contrast, the appalling injustices committed by so many of the adults.