What are analogies, and what are examples of analogies in Harper Lee's To Kill a Mockingbird?

Writers and speakers create analogies when they compare two different things or ideas with the purpose of explaining a vague or abstract concept by relating it to a concept more familiar or concrete. Similes and metaphors are types of analogies; however, analogies are much more developed in the sense that they aim to explain information, whereas similes and metaphors do not. The Literary Devices dictionary gives us the following example of an analogy:

Structure of an atom is like a solar system. Nucleus is the sun and electrons are the planets revolving around the sun. ("Analogy")

We can find many examples of analogies in Harper Lee's To Kill a Mockingbird.

One example can be found early on in the novel. Scout is very eager to begin going to school for the first time. But when her first grade teacher, Miss Caroline, discovers Scout can already read above her grade level, Scout is dismayed to have her reading abilities treated like a "crime" (Ch. 2). Miss Caroline also tells Scout to stop reading with her father since he doesn't know how to teach, which makes Scout very unhappy. She actually never learned how to read from Atticus but instead taught herself how to read by curling up in his lap each night and absorbing the words he was reading. Scout is so disheartened by the idea of having to give up reading that she realizes for the first time just how much she loves reading. Scout describes her love of reading by making an analogy to show just how much reading has become a central part of her being:

Until I feared I would lose it, I never loved to read. One does not love breathing. (Ch. 2)

In this analogy, Scout compares reading to breathing to show how central reading is to her existence by saying that we never really notice the things that are central to our existence, like breathing, until we're faced with the possibility of being without them.

A second analogy can be found towards the end of the book. Prior to the end, Scout was taught it is a sin to shoot mockingbirds because they do nothing but give us music all day long. In other words, Scout was taught it is a sin to kill or harm innocent beings that do nothing but bring pleasure. Scout shows she understands that the sin of killing mockingbirds can be applied to harming all innocent beings when she applies the concept to Arthur (Boo) Radley. Out on the porch with her father, Sheriff Tate, and Arthur, Scout comes to realize Arthur killed Bob Ewell to protect her and Jem from being killed by Ewell. Atticus is bent on taking the death of Ewell to court, thinking it was Jem who killed Ewell, but Sheriff Tate protests, knowing it was really Arthur who did so. Scout comes to understand Sheriff Tate is right and to agree with him. She then makes an analogy about the wrongfulness of exposing Arthur by bringing Ewell's death to court when she says the following to her father:

Yes, sir, I understand ... Mr. Tate was right ... Well, it'd be sort of like shootin' a mockingbird, wouldn't it? (Ch. 30)

In this analogy, the mockingbird represents innocent, caring Arthur, and shooting a mockingbird represents harming Arthur by exposing him.