From Gerald Frank Else, Aristotle's Poetics: The Argument
(Cambridge, Harvard University Press: 1957), pp. 306-307.
 

          Seen in the light of Platoís attacks on poetry, Aristotleís
theory is, depending on oneís point of view, either a liberation or a
condemnation.  The poet is released from Platoís requirement that he
must go to school to philosophy to learn the truth (the Ideas).  But he
is also condemned to the "practical" realm and must not claim that he
understands the ultimate things.  There is in fact not a word in the
Poetics about the ultimate "secrets of life," about why mankind should
suffer or be happy, about Fate, or manís relation to God, or any such
metaphysical matters.  These omissions are not accidental.  The proof is
that there is nothing about them in Aristotleís discussions of ethics or
politics either.  He has solved Platoís insistent question about the
metaphyiscal justification of poetry by begging the question: that is, by
assuming tacitly that poetry has no metaphyiscal dimension.

            Thus we are not to ask the poet for ultimate answers.
Aristotleís "practical" world, which is also his poetical world, is the
world as we know it from day to day: the realm in which we strive for
happiness through "virtue" and sometimes achieve it and sometimes fail,
in which we are what we are because of the choices we have made and what
we have done or failed to do.  God or Fate do not break into the charmed
circle.  The ultimate never confronts us in the Poetics, any more than it
does in the Ethics or the Politics - except in the form of Chance or the
marvelous ... .

            The poetic universal has nothing to do with what happens to
man from outside, but only with how he reacts to it ... .  What happens to
the tragic man, except so far as he himself is its cause, remains outside
the grasp of Aristotleís theory, or can appear in it only as an
inscrutable premise.  This had to be so, if not because Plato had laid it
down that God can only be the cause of good, then because Aristotle
excludes God from history and leaves no rationale for our fate except
what we ourselves do.  The paradox can be formulated in this way:
Aristotleís theory of the practical world has no room for any systematic
cause of action except man himself; yet the tragic "action" involves
not only manís own causality ... but something that breaks in upon him,
"happensí to him from outside.  Oedipus, the wise, kind, hot-blooded,
vital king, is all very well as the direct source of the actions that constitute
the play.  But these actions (...) would not constitute an action (...), and
certainly not a tragic action, were it not that something frightful has
happened to Oedipus.  Aristotleís theory can posit a character, Oedipus
the man; it cannot posit anything corresponding to account for Oedipus
the tragic victim.