If plot is the skeleton upon which the meat of your story hangs, then characters are surely the heart and soul.
Characterization is the art of presenting the people who populate your story.
Characterization is, in essence, nothing more — or less — than the depiction of motive (a word, incidentally, that comes from the Latin movere, meaning “to move or act”).
Thus it is primarily through actions and speech that a character’s traits are disclosed — which is why the act of compendiating in narrative passages a character’s thoughts and feelings do not alone develop character, though these passages do help, and telling, as opposed to merely showing, does have a legitimate place in storytelling.
The following, for example, illustrate the way in which even short passages of dialogue effectively develop a character:
“Why is it,” he said, one time, at the subway entrance, “I feel I’ve known you so many years?”
“Because I like you,” she said, “and I don’t want anything from you.”
(Ray Bradbury, Fahrenheit 451)
Eddie: “All right, I’m giving three-to-one odds I’ll have this fag licking my balls inside of three minutes.”
(Charles Bukowski, Barfly)
Algernon: Good Heavens! Is marriage so demoralizing at that?
Lane: I believe it is a very pleasant state, sir. I have had very little experience of it myself up to the present. I have only been married once. That was in consequence of a misunderstanding between myself and a young person.
Algernon: (Languidly.) I don’t know that I am much interested in your family life, Lane.
(Oscar Wilde, The Importance of Being Earnest, Act I, Scene I)
Just as in real life humans are evaluated by what we say and do, so in literature characters are also defined by what they say and do.
But what, finally, defines a character’s words and deeds?
What, for that matter, defines our words and deeds?
Only when we understand why a person does what she does do we begin to understand that person. And we understand someone well only when we understand the motives behind her actions.
“Human action is purposeful behavior,” said Ludwig von Mises, “and humans think not only for the sake of thinking but also in order to act.”
Yes: it is ultimately thought (or non-thought) that defines deeds, and thoughts, as we recently discussed, are shaped by words.
Literature is the artform of language. Literature is the artform of thought.
Character, both real and fictional, is determined by how thoroughly the author examines the thoughts that make the character act in the way she acts — and we are each the author of our own soul. The deeper the author delves into motive, the deeper we understand the character, and the more enriched our understanding of the human heart.