Part XVII 

In constructing the plot and working it out with the proper diction, the poet should place the scene, as far as possible, before his eyes. In this way, seeing everything with the utmost vividness, as if he were a spectator of the action, he will discover what is in keeping with it, and be most unlikely to overlook inconsistencies. The need of such a rule is shown by the fault found in Carcinus. Amphiaraus was on his way from the temple. This fact escaped the observation of one who did not see the situation. On the stage, however, the Piece failed, the audience being offended at the oversight. 
Again, the poet should work out his play, to the best of his power, with appropriate gestures; for those who feel emotion are most convincing through natural sympathy with the characters they represent; and one who is agitated storms, one who is angry rages, with the most lifelike reality. Hence poetry implies either a happy gift of nature or a strain of madness. In the one case a man can take the mould of any character; in the other, he is lifted out of his proper self. 
As for the story, whether the poet takes it ready made or constructs it for himself, he should first sketch its general outline, and then fill in the episodes and amplify in detail. The general plan may be illustrated by the Iphigenia. A young girl is sacrificed; she disappears mysteriously from the eyes of those who sacrificed her; she is transported to another country, where the custom is to offer up an strangers to the goddess. To this ministry she is appointed. Some time later her own brother chances to arrive. The fact that the oracle for some reason ordered him to go there, is outside the general plan of the play. The purpose, again, of his coming is outside the action proper. However, he comes, he is seized, and, when on the point of being sacrificed, reveals who he is. The mode of recognition may be either that of Euripides or of Polyidus, in whose play he exclaims very naturally: ‘So it was not my sister only, but I too, who was doomed to be sacrificed’; and by that remark he is saved. 
After this, the names being once given, it remains to fill in the episodes. We must see that they are relevant to the action. In the case of Orestes, for example, there is the madness which led to his capture, and his deliverance by means of the purificatory rite. In the drama, the episodes are short, but it is these that give extension to Epic poetry. Thus the story of the Odyssey can be stated briefly. A certain man is absent from home for many years; he is jealously watched by Poseidon, and left desolate. Meanwhile his home is in a wretched plight- suitors are wasting his substance and plotting against his son. At length, tempest-tost, he himself arrives; he makes certain persons acquainted with him; he attacks the suitors with his own hand, and is himself preserved while he destroys them. This is the essence of the plot; the rest is episode.
Part XVIII 
Every tragedy falls into two parts- Complication and Unraveling or Denouement. Incidents extraneous to the action are frequently combined with a portion of the action proper, to form the Complication; the rest is the Unraveling. By the Complication I mean all that extends from the beginning of the action to the part which marks the turning-point to good or bad fortune. The Unraveling is that which extends from the beginning of the change to the end. Thus, in the Lynceus of Theodectes, the Complication consists of the incidents presupposed in the drama, the seizure of the child, and then again … [the Unraveling] extends from the accusation of murder to 
There are four kinds of Tragedy: the Complex, depending entirely on Reversal of the Situation and Recognition; the Pathetic (where the motive is passion)- such as the tragedies on Ajax and Ixion; the Ethical (where the motives are ethical)- such as the Phthiotides and the Peleus. The fourth kind is the Simple. [We here exclude the purely spectacular element], exemplified by the Phorcides, the Prometheus, and scenes laid in Hades. The poet shouldendeavor, if possible, to combine all poetic elements; or failing that, the greatest number and those the most important; the more so, in face of the caviling criticism of the day. For whereas there have hitherto been good poets, each in his own branch, the critics now expect one man to surpass all others in their several lines of excellence. 
In speaking of a tragedy as the same or different, the best test to take is the plot. Identity exists where the Complication and Unraveling are the same. Many poets tie the knot well, but unravel it Both arts, however, should always be mastered. 
Again, the poet should remember what has been often said, and not make an Epic structure into a tragedy- by an Epic structure I mean one with a multiplicity of plots- as if, for instance, you were to make a tragedy out of the entire story of the Iliad. In the Epic poem, owing to its length, each part assumes its proper magnitude. In the drama the result is far from answering to the poet’s expectation. The proof is that the poets who have dramatized the whole story of the Fall of Troy, instead of selecting portions, like Euripides; or who have taken the whole tale of Niobe, and not a part of her story, like Aeschylus, either fail utterly or meet with poor success on the stage. Even Agathon has been known to fail from this one defect. In his Reversals of the Situation, however, he shows a marvelous skill in the effort to hit the popular taste- to produce a tragic effect that satisfies the moral sense. This effect is produced when the clever rogue, like Sisyphus, is outwitted, or the brave villain defeated. Such an event is probable in Agathon’s sense of the word: ‘is probable,’ he says, ‘that many things should happen contrary to probability.’ 
The Chorus too should be regarded as one of the actors; it should be an integral part of the whole, and share in the action, in the manner not of Euripides but of Sophocles. As for the later poets, their choral songs pertain as little to the subject of the piece as to that of any other tragedy. They are, therefore, sung as mere interludes- a practice first begun by Agathon. Yet what difference is there between introducing such choral interludes, and transferring a speech, or even a whole act, from one play to another.
Part XIX 
It remains to speak of Diction and Thought, the other parts of Tragedy having been already discussed. concerning Thought, we may assume what is said in the Rhetoric, to which inquiry the subject more strictly belongs. Under Thought is included every effect which has to be produced by speech, the subdivisions being: proof and refutation; the excitation of the feelings, such as pity, fear, anger, and the like; the suggestion of importance or its opposite. Now, it is evident that the dramatic incidents must be treated from the same points of view as the dramatic speeches, when the object is to evoke the sense of pity, fear, importance, or probability. The only difference is that the incidents should speak for themselves without verbal exposition; while effects aimed at in should be produced by the speaker, and as a result of the speech. For what were the business of a speaker, if the Thought were revealed quite apart from what he says? 

Next, as regards Diction. One branch of the inquiry treats of the Modes of Utterance. But this province of knowledge belongs to the art of Delivery and to the masters of that science. It includes, for instance- what is a command, a prayer, a statement, a threat, a question, an answer, and so forth. To know or not to know these things involves no serious censure upon the poet’s art. For who can admit the fault imputed to Homer by Protagoras- that in the words, ‘Sing, goddess, of the wrath, he gives a command under the idea that he utters a prayer? For to tell some one to do a thing or not to do it is, he says, a command. We may, therefore, pass this over as an inquiry that belongs to another art, not to poetry.
Poetics By Aristotle