Posterior Analytics   

33

Scientific knowledge and its object differ from opinion and the
object of opinion in that scientific knowledge is commensurately
universal and proceeds by necessary connexions, and that which is
necessary cannot be otherwise. So though there are things which are
true and real and yet can be otherwise, scientific knowledge clearly
does not concern them: if it did, things which can be otherwise
would be incapable of being otherwise. Nor are they any concern of
rational intuition-by rational intuition I mean an originative
source of scientific knowledge-nor of indemonstrable knowledge,
which is the grasping of the immediate premiss. Since then rational
intuition, science, and opinion, and what is revealed by these
terms, are the only things that can be 'true', it follows that it is
opinion that is concerned with that which may be true or false, and
can be otherwise: opinion in fact is the grasp of a premiss which is
immediate but not necessary. This view also fits the observed facts,
for opinion is unstable, and so is the kind of being we have described
as its object. Besides, when a man thinks a truth incapable of being
otherwise he always thinks that he knows it, never that he opines
it. He thinks that he opines when he thinks that a connexion, though
actually so, may quite easily be otherwise; for he believes that
such is the proper object of opinion, while the necessary is the
object of knowledge.
In what sense, then, can the same thing be the object of both
opinion and knowledge? And if any one chooses to maintain that all
that he knows he can also opine, why should not opinion be
knowledge? For he that knows and he that opines will follow the same
train of thought through the same middle terms until the immediate
premisses are reached; because it is possible to opine not only the
fact but also the reasoned fact, and the reason is the middle term; so
that, since the former knows, he that opines also has knowledge.
The truth perhaps is that if a man grasp truths that cannot be other
than they are, in the way in which he grasps the definitions through
which demonstrations take place, he will have not opinion but
knowledge: if on the other hand he apprehends these attributes as
inhering in their subjects, but not in virtue of the subjects'
substance and essential nature possesses opinion and not genuine
knowledge; and his opinion, if obtained through immediate premisses,
will be both of the fact and of the reasoned fact; if not so obtained,
of the fact alone. The object of opinion and knowledge is not quite
identical; it is only in a sense identical, just as the object of true
and false opinion is in a sense identical. The sense in which some
maintain that true and false opinion can have the same object leads
them to embrace many strange doctrines, particularly the doctrine that
what a man opines falsely he does not opine at all. There are really
many senses of 'identical', and in one sense the object of true and
false opinion can be the same, in another it cannot. Thus, to have a
true opinion that the diagonal is commensurate with the side would
be absurd: but because the diagonal with which they are both concerned
is the same, the two opinions have objects so far the same: on the
other hand, as regards their essential definable nature these
objects differ. The identity of the objects of knowledge and opinion
is similar. Knowledge is the apprehension of, e.g. the attribute
'animal' as incapable of being otherwise, opinion the apprehension
of 'animal' as capable of being otherwise-e.g. the apprehension that
animal is an element in the essential nature of man is knowledge;
the apprehension of animal as predicable of man but not as an
element in man's essential nature is opinion: man is the subject in
both judgements, but the mode of inherence differs.
This also shows that one cannot opine and know the same thing
simultaneously; for then one would apprehend the same thing as both
capable and incapable of being otherwise-an impossibility. Knowledge