for there is indeed a vast difference between what happens propter hoc and post hoc.
A "reversal" is a change of the situation into the opposite, as described above, [Note] this change being, moreover, as we are saying, probable or inevitable—
like the man in the Oedipus who came to cheer Oedipus and rid him of his anxiety about his mother by revealing his parentage and changed the whole situation. [Note] In the Lynceus, too, there is the man led off to execution and
Danaus following to kill him, and the result of what had already happened was that the latter was killed and the former escaped. [Note]
A "discovery," as the term itself implies, is a change from ignorance to knowledge, producing either friendship or hatred in those who are destined for good fortune or ill.
A discovery is most effective when it coincides with reversals, such as that involved by the discovery in the Oedipus.
There are also other forms of discovery, for what we have described may in a sense occur in relation to inanimate and trivial objects, or one may discover whether some one has done something or not.
But the discovery which is most essentially part of the plot and part of the action is of the kind described above, for such a discovery and reversal of fortune will involve either pity or fear,