The Complete Aristotle (eng.)

was only at the actual moment at which he was being led on
to recognize this as true in the instance before him that he came
to know ‘this figure inscribed in the semicircle’ to be a triangle.
For some things (viz. the singulars finally reached which are not
predicable of anything else as subject) are only learnt in this
way, i.e. there is here no recognition through a middle of a minor
term as subject to a major. Before he was led on to recognition or
before he actually drew a conclusion, we should perhaps say that in
a manner he knew, in a manner not.
    If he did not in an unqualified sense of the term know the
existence of this triangle, how could he know without qualification
that its angles were equal to two right angles? No: clearly he
knows not without qualification but only in the sense that he knows
universally. If this distinction is not drawn, we are faced with
the dilemma in the Meno: either a man will learn nothing or what he
already knows; for we cannot accept the solution which some people
offer. A man is asked, ‘Do you, or do you not, know that every pair
is even?’ He says he does know it. The questioner then produces a
particular pair, of the existence, and so a fortiori of the
evenness, of which he was unaware. The solution which some people
offer is to assert that they do not know that every pair is even,
but only that everything which they know to be a pair is even: yet
what they know to be even is that of which they have demonstrated
evenness, i.e. what they made the subject of their premiss, viz.
not merely every triangle or number which they know to be such, but
any and every number or triangle without reservation. For no
premiss is ever couched in the form ‘every number which you know to
be such’, or ‘every rectilinear figure which you know to be such’:
the predicate is always construed as applicable to any and every
instance of the thing. On the other hand, I imagine there is
nothing to prevent a man in one sense knowing what he is learning,
in another not knowing it. The strange thing would be, not if in
some sense he knew what he was learning, but if he were to know it
in that precise sense and manner in which he was learning it.
2
    We suppose ourselves to possess unqualified scientific knowledge
of a thing, as opposed to knowing it in the accidental way in which
the sophist knows, when we think that we know the cause on which
the fact depends, as the cause of that fact and of no other, and,
further, that the fact could not be other than it is. Now that
scientific knowing is something of this sort is evident-witness
both those who falsely claim it and those who actually possess it,
since the former merely imagine themselves to be, while the latter
are also actually, in the condition described. Consequently the
proper object of unqualified scientific knowledge is something
which cannot be other than it is.
    There may be another manner of knowing as well-that will be
discussed later. What I now assert is that at all events we do know
by demonstration. By demonstration I mean a syllogism productive of
scientific knowledge, a syllogism, that is, the grasp of which is
eo ipso such knowledge. Assuming then that my thesis as to the
nature of scientific knowing is correct, the premisses of
demonstrated knowledge must be true, primary, immediate, better
known than and prior to the conclusion, which is further related to
them as effect to cause. Unless these conditions are satisfied, the
basic truths will not be ‘appropriate’ to the conclusion. Syllogism
there may indeed be without these conditions, but such syllogism,
not being productive of scientific knowledge, will not be
demonstration. The premisses must be true: for that which is
non-existent cannot be known-we cannot know, e.g. that the diagonal
of a square is commensurate with its side. The premisses must be
primary and indemonstrable; otherwise they will require
demonstration in order to be known, since to have knowledge, if it
be not accidental knowledge, of things which are demonstrable,
means precisely to have a demonstration of them. The premisses must
be the causes of the conclusion, better known than it, and prior to
it; its causes, since we possess scientific knowledge of a thing
only when we know its cause; prior, in order to be causes;
antecedently known, this antecedent knowledge being not our mere
understanding of the meaning, but knowledge of the fact as well.
Now ‘prior’ and ‘better known’ are