Aristotle turns his attention toward the character of the tragic hero and lays out four requirements. First, the hero must be good. The character of the hero denotes the hero's moral purpose in the play, and a good character will have a good moral purpose. Second, the good qualities of the hero must be appropriate to the character. For instance, warlike qualities can be good, but they would be inappropriate in a woman. Third, the hero must be realistic. In other words, if he is drawn from myth, he should be a reasonable semblance of the character portrayed in myths. Fourth, the hero must be consistent (by which Aristotle means the hero must be written consistently, not that the hero must behave consistently). He accepts that some characters are inconsistent but that they should be written so as to be consistent in their inconsistency. Like the plot itself, the behavior of the characters should be seen as necessary or probable, in accordance with the internal logic of their personality. Thus, a character may behave inconsistently so long as we can perceive this inconsistency as stemming from a personality that is internally consistent.
From these requirements, Aristotle thinks it clear that the lusis, or denouement, should arise out of the plot and not depend upon stage artifice. Both the characters and the plot ought to follow a probable or necessary sequence, so that the lusis should be a part of this sequence. Improbable events, or the intervention of the gods, should be reserved for events outside the action of the play or events beyond human knowledge. The actual incidents themselves should not rely on miracles but on probability and necessity.
In order to reconcile the first requirement—that the hero be good—with the third requirement—that the hero be realistic—Aristotle recommends that the poet should keep all the distinctive characteristics of the person being portrayed but touch them up a little to make the hero appear better than he is. For instance, in the Iliad , Homer repeatedly describes Achilles' hot temper and yet makes him seem exceedingly good and heroic nonetheless.
In Chapter 6, Aristotle outlines the six different parts of tragedy, denoting character and thought as attributes of the agents in the tragedy. Roughly speaking, character denotes the moral aspects of an agent, while thought denotes the intellectual aspects. Thought is generally exhibited in speeches that enunciate general truths and the like. An agent's thoughts are, roughly, what he or she shares in common with everyone else and what can be expressed clearly and directly to other people. Character is what is unique to each individual agent. What people want, what their motives are, what they are willing to do to get what they want, why they want what they want—all of these fall within the realm of character.
We might clarify the distinction between thought and character by saying that thought can be expressed directly, whereas character must be inferred. Let us take as an example the famous "to be or not to be" speech in Hamlet . Hamlet is debating whether or not he should commit suicide, reasoning on the one hand that this life is full of pain and misery and death is a quick way out, but on the other hand that no one knows what happens after death and that perhaps death is even worse than life. Thought is expressed in Hamlet's reasoning: we can all understand his reasons, and we can then think for ourselves which reasons are good and which are bad. Character is more subtle and complicated. The thoughts Hamlet expresses are universally understood and recognizable, but the kind of character that Hamlet must have to enunciate these thoughts is far from clear. Why is Hamlet contemplating suicide? What makes him offer these reasons and express them in this way? Why does he find the reasons against suicide more compelling? What, ultimately, does he want to do? Understanding thoughts is a simple matter of interpretation; understanding character is an uncertain procedure that requires penetrating psychological insight. We might say that the character of an agent is everything about the agent that cannot be put into words.
Given the difficulties of understanding character, Aristotle seems to treat it in a very uncomplicated way. The first and second requirements basically demand that the tragic hero be of good and appropriate character. That is, his motives, desires, ambitions, etc., ought to be admirable to some extent and well suited to his station in life. Beyond that, they must be true to what the audience already knows of the hero (the third requirement), and the hero's behavior must be consistent (the fourth requirement).
The demand that the characters be consistent is in many ways parallel to Aristotle's demand for the unity of plot. Every action in the plot should be causally connected to every other action. The tragedy, viewed as a whole, should have the internal consistency of a clock, so that we should see a near inevitability in the way things turned out. Similarly, an agent should behave in such a way that every decision, every action, can be read as a manifestation of a single, unified character. Characters, too, should have the regularity of a clock, so that, when viewed as a whole, there should be a seeming inevitability in every decision the hero makes, based on what we know of the hero's character.
Aristotle does not rule out entirely that a hero could behave inconsistently, but he demands that the play, seen as a whole, should make this inconsistency comprehensible. Though in one instance the hero may behave one way, and in another behave in a contradictory manner, this contradiction should be made clear by the larger context. Aristotle condemns plays where inconsistent or puzzling behavior is never clarified.
Aristotle's hero must be of high rank, relatively virtuous, true to life, and consistent. These requirements depend to some extent on a relatively transparent moral worldview and understanding of psychology. In a world where motives are unclear and there are layers of psychology to work through, it might be difficult to determine whether a character is ultimately "good," or what goodness consists of. Further, a character may seem inconsistent, or at least ambiguous, if the agent's motives don't float to the surface by the end of the play. Euripides in particular is known for writing plays full of moral and psychological ambiguity. Not surprisingly, Aristotle seems to prefer the much cleaner Sophocles to Euripides. In retrospect, though, this seems more a matter of taste than of irrefutable reasoning.