Posterior Analytics   

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 ambiguous terms, for there is a difference between what
is prior and better known in the order of being and what is prior
and better known to man. I mean that objects nearer to sense are prior
and better known to man; objects without qualification prior and
better known are those further from sense. Now the most universal
causes are furthest from sense and particular causes are nearest to
sense, and they are thus exactly opposed to one another. In saying
that the premisses of demonstrated knowledge must be primary, I mean
that they must be the 'appropriate' basic truths, for I identify
primary premiss and basic truth. A 'basic truth' in a demonstration is
an immediate proposition. An immediate proposition is one which has no
other proposition prior to it. A proposition is either part of an
enunciation, i.e. it predicates a single attribute of a single
subject. If a proposition is dialectical, it assumes either part
indifferently; if it is demonstrative, it lays down one part to the
definite exclusion of the other because that part is true. The term
'enunciation' denotes either part of a contradiction indifferently.
A contradiction is an opposition which of its own nature excludes a
middle. The part of a contradiction which conjoins a predicate with
a subject is an affirmation; the part disjoining them is a negation. I
call an immediate basic truth of syllogism a 'thesis' when, though
it is not susceptible of proof by the teacher, yet ignorance of it
does not constitute a total bar to progress on the part of the
pupil: one which the pupil must know if he is to learn anything
whatever is an axiom. I call it an axiom because there are such truths