This is evidently a
distinct fourth class.
In general, if we search for the elements of existing things
without distinguishing the many senses in which things are said to
exist, we cannot find them, especially if the search for the
elements of which things are made is conducted in this manner. For
it is surely impossible to discover what 'acting' or 'being acted on',
or 'the straight', is made of, but if elements can be discovered at
all, it is only the elements of substances; therefore either to seek
the elements of all existing things or to think one has them is
incorrect.
And how could we learn the elements of all things? Evidently we
cannot start by knowing anything before. For as he who is learning
geometry, though he may know other things before, knows none of the
things with which the science deals and about which he is to learn, so
is it in all other cases. Therefore if there is a science of all
things, such as some assert to exist, he who is learning this will
know nothing before. Yet all learning is by means of premisses which
are (either all or some of them) known before,-whether the learning be
by demonstration or by definitions; for the elements of the definition
must be known before and be familiar; and learning by induction
proceeds similarly. But again, if the science were actually innate, it
were strange that we are unaware of our possession of the greatest
of sciences.
Again, how is one to come to know what all things are made of, and
how is this to be made evident? This also affords a difficulty; for
there might be a conflict of opinion, as there is about certain
syllables; some say za is made out of s and d and a, while others
say it is a distinct sound and none of those that are familiar.
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