The Complete Aristotle (eng.)

visible difference, is not an organic part of the
whole.
IX
    It is, moreover, evident from what has been said, that it is not
the function of the poet to relate what has happened, but what may
happen—what is possible according to the law of probability or
necessity. The poet and the historian differ not by writing in
verse or in prose. The work of Herodotus might be put into verse,
and it would still be a species of history, with meter no less than
without it. The true difference is that one relates what has
happened, the other what may happen. Poetry, therefore, is a more
philosophical and a higher thing than history: for poetry tends to
express the universal, history the particular. By the universal I
mean how a person of a certain type on occasion speak or act,
according to the law of probability or necessity; and it is this
universality at which poetry aims in the names she attaches to the
personages. The particular is—for example—what Alcibiades did or
suffered. In Comedy this is already apparent: for here the poet
first constructs the plot on the lines of probability, and then
inserts characteristic names—unlike the lampooners who write about
particular individuals. But tragedians still keep to real names,
the reason being that what is possible is credible: what has not
happened we do not at once feel sure to be possible; but what has
happened is manifestly possible: otherwise it would not have
happened. Still there are even some tragedies in which there are
only one or two well-known names, the rest being fictitious. In
others, none are well known—as in Agathon’s Antheus, where
incidents and names alike are fictitious, and yet they give none
the less pleasure. We must not, therefore, at all costs keep to the
received legends, which are the usual subjects of Tragedy. Indeed,
it would be absurd to attempt it; for even subjects that are known
are known only to a few, and yet give pleasure to all. It clearly
follows that the poet or ‘maker’ should be the maker of plots
rather than of verses; since he is a poet because he imitates, and
what he imitates are actions. And even if he chances to take a
historical subject, he is none the less a poet; for there is no
reason why some events that have actually happened should not
conform to the law of the probable and possible, and in virtue of
that quality in them he is their poet or maker.
    Of all plots and actions the episodic are the worst. I call a
plot ‘episodic’ in which the episodes or acts succeed one another
without probable or necessary sequence. Bad poets compose such
pieces by their own fault, good poets, to please the players; for,
as they write show pieces for competition, they stretch the plot
beyond its capacity, and are often forced to break the natural
continuity.
    But again, Tragedy is an imitation not only of a complete
action, but of events inspiring fear or pity. Such an effect is
best produced when the events come on us by surprise; and the
effect is heightened when, at the same time, they follows as cause
and effect. The tragic wonder will then be greater than if they
happened of themselves or by accident; for even coincidences are
most striking when they have an air of design. We may instance the
statue of Mitys at Argos, which fell upon his murderer while he was
a spectator at a festival, and killed him. Such events seem not to
be due to mere chance. Plots, therefore, constructed on these
principles are necessarily the best.
X
    Plots are either Simple or Complex, for the actions in real
life, of which the plots are an imitation, obviously show a similar
distinction. An action which is one and continuous in the sense
above defined, I call Simple, when the change of fortune takes
place without Reversal of the Situation and without Recognition
    A Complex action is one in which the change is accompanied by
such Reversal, or by Recognition, or by both. These last should
arise from the internal structure of the plot, so that what follows
should be the necessary or probable result of the preceding action.
It makes all the difference whether any given event is a case of
propter hoc or post hoc.
XI
    Reversal of the Situation is a change by which the action veers
round to its opposite, subject always to our rule of probability or
necessity. Thus in the Oedipus, the messenger comes to cheer
Oedipus and free him from his alarms about his mother, but by
revealing who he is, he produces the opposite effect. Again in the
Lynceus, Lynceus is