when for instance brother kills brother, or son father, or mother son, or son mother—either kills or intends to kill, or does something of the kind, that is what we must look for.
Now it is not right to break up the traditional stories, I mean, for instance, Clytaemnestra being killed by Orestes and Eriphyle by Alcmaeon,
but the poet must show invention and make a skilful use of the tradition.
But we must state more clearly what is meant by "skilful."
The action may happen in the way in which the old dramatists made their characters act—consciously and knowing the facts, as Euripides [Note] also made his Medea kill her children.
Or they may do the deed but without realizing the horror of it and then discover the relationship afterwards, like Oedipus in Sophocles. That indeed lies outside the play, [Note] but an example of this in the tragedy itself is the Alcmaeon of Astydamas [Note] or Telegonus in the Wounded Odysseus.
A third alternative is to intend to do some irremediable action in ignorance and to discover the truth before doing it.
Besides these there is no other way, for they must either do the deed or not, either knowing or unknowing.
The worst of these is to intend the action with full knowledge and not to perform it. That outrages the feelings and is not tragic, for there is no calamity.