The essence of the novel is conflict. Human beings are hard-wired to be attracted to stories with conflict.
There are two kinds of conflict: external and internal. External conflict usually takes place between a person and another person or persons, event, or situation. The main character can be a person, animal, force of nature, institution, machine, and so forth. All that matters is that they stand in opposition to each other. Think of “Call of the Wild,” “Moby Dick,” and “The Three Little Pigs.”
Some writing teachers have tried to list all the possible kinds of conflict between the main character (protagonist) and the principal character in opposition to the main character (antagonist). The list can grow into the dozens, including such plots as person against person, person against nature, person against time, and so forth.
As a main character tries to resolve a problem or achieve a goal, he or she inevitably encounters conflict of one sort or another.
Internal conflict, as opposed to external, involves conflicting mental or emotional forces within the mind of the main character. The main character struggles with himself or herself. Internal conflict takes place within a person’s mind, such as a struggle to make a decision or overcome a feeling.
Think of the play “Hamlet.” The Prince agonizes over how, if, and when to avenge his father’s death. To deepen the novel (and make it more interesting), modern writers often include both external and internal conflict.
In the novel, internal conflict adds to suspense about if, when, or how the internal conflict is resolved. The opposition might involve conflicting morals, beliefs about right and wrong, make tough decisions, and so forth.
Some writing teachers insist that the main character undergo a psychological change as a result of the internal conflict. Contrary to some schools of thought, though, the main character does not absolutely have to change – although it can be very satisfying to the reader if she or he does. In some stories, the main character resolves his internal conflict by sticking with his own approach. Think of Horatio-Alger-type stories.
Taken together, external and internal conflict force a character to make choices and changes. Choices create tension in the novel as the reader’s interest is piqued as to how the tension will be resolved. Thus they propel the most memorable and captivating plots.
As you write, try to instill conflict on every page.