Poetics

The work called Poetics covers, in the main, tragedy, and has something to say about epic as well. Aristotle's writing on comedy is lost (the novel The Name of the Rose involves discovery of a manuscript of it: I recommend that book: the movie isn't bad either).

The enterprise that Aristotle was engaged in includes a good deal of literary theory and criticism, but it is not primarily trying to be literary criticism. Aristotle is not trying to produce a theory of poetry, or of tragedy, that will hold good for all time. He is trying to tell a Greek audience how to produce a Greek play in the tragic tradition. This is important, because many people read it to find Aristotle's literary theory: that is not an easy task.

The Poetics includes introductory remarks on the nature of poetry and imitation as well as its history. Then the main body of the  work is about tragedy. A quick discussion of epic follows. Then Aristotle compares the two and raises some literary-critical questions.

Aristotle says that poetry is imitative. It imitates in words. So what is imitation?
Plato: narration versus drama.
Counterfeit versus mimic
Making a likeness
Representing
Recreating
Fiction
Token versus type (representing this picnic versus representing a picnic).
Imagine something, then describe it...

FYI: Merriam-Webster's Third New International Dictionary definition of "imitate":

1. an assumption of or mimicking of the form of something that serves or is regarded as a model "imitation is the sincerest form of flattery" "the imitation of leaves by certain butterflies is unbelievably perfect" "a style developed in imitation of classic models"
2. something that is made or produced as a copy : an artificial likeness : COUNTERFEIT "risible imitations of his schoolfellows" "a convincing imitation of colonial architecture"
3. a : a literary work or composition designed to reproduce the style or manner of another author  b : a free translation or an adaptation or parody especially when involving transformation of cultural, social, or temporal situation
4. the repetition in a voice part of the melodic theme, phrase, or motive previously found in another part
5. a in Platonism   : the process through which a sensible object is informed by or participates in a subsistent idea or transcendent archetype  b in Aristotelianism   (1) : the artistic simulation of anything as it is actually (2) : its representation as it is ideally or as it ought to be
6. a : the execution of an act supposedly as a direct response to the perception of another person performing the act  b : the assumption of the modes of behavior observed in other individuals

It is not clear what Aristotle means by imitation (the definition from the dictionary given above of Aristotelian imitation is hard to swallow: can you imitate Oedipus? how is he "actually"?). It is clear that it is closest to representation, but it is also clear that it is closer to fiction than non-fiction.

Aristotle says we are natural imitators and that we take pleasure in it.

• everyone enjoys imitation. A sign of that is what happens in actual cases; for we enjoy looking at very accurate likenesses of things which in themselves are painful to see--for example, the forms of the foulest animals, and corpses. The reason for this is that learning is most pleasant not only to philosophers but also to other humas, even if they share the pleasure briefly. That is why we enjoy seeing likenesses--as we look, we learn and infer what each thing is..
• First,  the instinct of imitation is implanted in man from childhood, one difference between him and other animals being that he is the most imitative of living creatures,  and through imitation learns his earliest lessons; and no  less universal is the pleasure felt in things imitated.  We have evidence of this in the facts of experience.  Objects which in themselves we view with pain, we delight  to contemplate when reproduced with minute fidelity    [Poetics Chapter lV]
  

Perhaps what Aristotle means is that poetry represents something that is universal about life by means of presenting actions that involve both necessary and probable components.

• What it re-presents: Our character is the traits we were caused to have or acquired voluntarily. Our actions show our character and determine whether we will be happy. Literature shows actions at crucial moments via plot.  Tragedy should show complex actions leading the hero to a reversal of fortune because of a mistake.  Pity and fear are excited by that.
  
• the historian, however, by contrast with the poet, describes what has happened, whereas the poet describes the sort of things that would happen. This is why poetry is more philosophical and more serious than history; for it speaks more of what is universal, whereas history speaks of what is particular.
  

Tragedy

Aristotle wrote about tragedy as he knew it, and it is unfair to expect him to write about tragedy as we know it, drama as we know it, or poetry in general as we know it, for art, more than many things, is a matter of convention. He was reacting to the phenomena he observed.

Aristotle's definition of tragedy:

• A tragedy is the imitation of an action which is serious and, having grandeur, complete in itself, done in language seasoned with embellishments, each appearing separately in different parts of the work, in dramatic rather than narrative form, accomplishing by way of pity and fear the catharsis of such feelings. 1449b22-28

action:
serious:
complete:
language:
embellishments (separately appearing):
parts: plot, character, diction,  thought, spectacle (special effects), and music/song. What of dance?
dramatic:
catharsis: purification or purgation (of what?)

pity and fear: for whom? for what? does it fit Aristotle's def. of pity in the Rhetoric? the pity and fear cause pleasure (so they are not really pity and fear?) 1453b12? pity and fear specifically or just emotions like them? quasi-emotions?

Did Shakespeare write tragedy? the answer must be no, if we follow A's definition. Neither did O'Neill or Ibsen, who are also among the supposedly greatest tragedians.

The tragic hero:

• There remains, then, the intermediate kind of person, a man not preeminently virtuous or just, but who enjoys a high reputation and prosperity, whose misfortune is brought upon him not by vice and depravity but by some fault. 1453a6-10

This "fault" is famous: it is a translation of the Greek word hamartia, which means 'fault' but also means a mistake: it is the "action" of tragedy: the misfortune which follows is undeserved, so it's not a sin.
Does tragedy then arouse the feeling we have when we observe bad luck?

Unity:
Classic modern drama obeys the supposed unities of drama: action, time, and place. The unity of action is the one that Aristotle explicitly asks for.
A complete action has a beginning, middle, and an end: good plots resemble living organisms.

• tragedy is an imitation not of people but of action and of life...In a play, then, people do not act in order to portray character: they include character for the sake of action. 1450a16-21

Plot elements:

• anagnorisis: recognition (Oedipus recognizes that he has killed his father and slept with his mother)
• peripateia: reversal of fortune (Oedipus goes from king to blind exile)
  

Pity:
W3 definitions:

1. archaic: MERCY, CLEMENCY "saw that his judge was inclining to mercy, and he renewed his appeals for pity" J.H.Shorthouse
2. a (1) : sympathetic heartfelt sorrow for one that is suffering physically or mentally or that is otherwise distressed or unhappy (as through misfortune, difficulties) : COMPASSION, COMMISERATION "felt the deepest pity for the prisoners" (2) : the capacity to feel such sorrow "was habitually hardhearted and without pity"  b : a somewhat disdainful or contemptuous feeling of regret over the condition of one viewed by the speaker as in some way inferior or reprehensible "leaves us less with a sense of repugnance ... than with a sense of pity for the man who could think of nothing better" T.S.Eliot
3. a cause of regret : a condition or circumstance that is to be regretted "what a pity that you didn't get here sooner"