Conflict is a necessary element of fictional literature. It usually takes the form of an entity versus either

• another entity,
• society,
• nature, or
• his, her, or itself.

When an entity is in conflict with his, her, or itself, the conflict is categorized as internal. Otherwise, it is external.

As with other literary terms, these have come about gradually as descriptions of common narrative structures. Conflict was first described in ancient Greek literature as the agon, or central contest in tragedy. In order to hold the interest, the hero must have a single (according to Aristotle) conflict. The agon, or act of conflict, involve the pro-tagonist and the ant-agonist, corresponding to the hero and villain. For the hero, there must be an opponent. The outcome of the contest cannot be known in advance, and the hero's struggle should be, (according to later critics such as Plutarch), ennobling. Even in contemporary, non-dramatic literature, critics have observed that the agon is the central unit of the plot. To the degree that the protagonist can easily triumph, the less value there is in the drama. In internal and external conflict alike, the antagonist must act upon the protagonist and must seem to overmatch him or her. For example, in William Faulkner's The Bear, nature might be the antagonist. Even though it is an abstraction, natural creatures and the scenery oppose and resist the protagonist. In the same story, the young boy's doubts about himself provide an internal conflict, and they seem to overwhelm him. On the other hand, when godlike characters enter (e.g. in Superman), great villains have to be created, or natural weaknesses have to be invented, to allow the narrative to have drama.