350 BC

                              POSTERIOR ANALYTICS

                                  by Aristotle

                          translated by G. R. G. Mure

                              Book I

                                 1

  ALL instruction given or received by way of argument proceeds from
pre-existent knowledge. This becomes evident upon a survey of all
the species of such instruction. The mathematical sciences and all
other speculative disciplines are acquired in this way, and so are the
two forms of dialectical reasoning, syllogistic and inductive; for
each of these latter make use of old knowledge to impart new, the
syllogism assuming an audience that accepts its premisses, induction
exhibiting the universal as implicit in the clearly known
particular. Again, the persuasion exerted by rhetorical arguments is
in principle the same, since they use either example, a kind of
induction, or enthymeme, a form of syllogism.

  The pre-existent knowledge required is of two kinds. In some cases
admission of the fact must be assumed, in others comprehension of
the meaning of the term used, and sometimes both assumptions are
essential. Thus, we assume that every predicate can be either truly
affirmed or truly denied of any subject, and that 'triangle' means
so and so; as regards 'unit' we have to make the double assumption
of the meaning of the word and the existence of the thing. The
reason is that these several objects are not equally obvious to us.
Recognition of a truth may in some cases contain as factors both
previous knowledge and also knowledge acquired simultaneously with
that recognition-knowledge, this latter, of the particulars actually
falling under the universal and therein already virtually known. For
example, the student knew beforehand that the angles of every triangle
are equal to two right angles; but it 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