It appears then from these considerations that
neither definition and syllogism nor their objects are identical,
and further that definition neither demonstrates nor proves
anything, and that knowledge of essential nature is not to be obtained
either by definition or by demonstration.
8
We must now start afresh and consider which of these conclusions are
sound and which are not, and what is the nature of definition, and
whether essential nature is in any sense demonstrable and definable or
in none.
Now to know its essential nature is, as we said, the same as to know
the cause of a thing's existence, and the proof of this depends on the
fact that a thing must have a cause. Moreover, this cause is either
identical with the essential nature of the thing or distinct from
it; and if its cause is distinct from it, the essential nature of
the thing is either demonstrable or indemonstrable. Consequently, if
the cause is distinct from the thing's essential nature and
demonstration is possible, the cause must be the middle term, and, the
conclusion proved being universal and affirmative, the proof is in the
first figure.
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