The Complete Aristotle (eng.)

clearly metaphors and metaphorical expressions
are precluded in definition: otherwise dialectic would involve
metaphors.
14
    In order to formulate the connexions we wish to prove we have to
select our analyses and divisions. The method of selection consists
in laying down the common genus of all our subjects of
investigation-if e.g. they are animals, we lay down what the
properties are which inhere in every animal. These established, we
next lay down the properties essentially connected with the first
of the remaining classes-e.g. if this first subgenus is bird, the
essential properties of every bird-and so on, always characterizing
the proximate subgenus. This will clearly at once enable us to say
in virtue of what character the subgenera-man, e.g. or
horse-possess their properties. Let A be animal, B the properties
of every animal, C D E various species of animal. Then it is clear
in virtue of what character B inheres in D-namely A-and that it
inheres in C and E for the same reason: and throughout the
remaining subgenera always the same rule applies.
    We are now taking our examples from the traditional class-names,
but we must not confine ourselves to considering these. We must
collect any other common character which we observe, and then
consider with what species it is connected and what.properties
belong to it. For example, as the common properties of horned
animals we collect the possession of a third stomach and only one
row of teeth. Then since it is clear in virtue of what character
they possess these attributes-namely their horned character-the
next question is, to what species does the possession of horns
attach?
    Yet a further method of selection is by analogy: for we cannot
find a single identical name to give to a squid’s pounce, a fish’s
spine, and an animal’s bone, although these too possess common
properties as if there were a single osseous nature.
15
    Some connexions that require proof are identical in that they
possess an identical ‘middle’ e.g. a whole group might be proved
through ‘reciprocal replacement’-and of these one class are
identical in genus, namely all those whose difference consists in
their concerning different subjects or in their mode of
manifestation. This latter class may be exemplified by the
questions as to the causes respectively of echo, of reflection, and
of the rainbow: the connexions to be proved which these questions
embody are identical generically, because all three are forms of
repercussion; but specifically they are different.
    Other connexions that require proof only differ in that the
‘middle’ of the one is subordinate to the ‘middle’ of the other.
For example: Why does the Nile rise towards the end of the month?
Because towards its close the month is more stormy. Why is the
month more stormy towards its close? Because the moon is waning.
Here the one cause is subordinate to the other.
16
    The question might be raised with regard to cause and effect
whether when the effect is present the cause also is present;
whether, for instance, if a plant sheds its leaves or the moon is
eclipsed, there is present also the cause of the eclipse or of the
fall of the leaves-the possession of broad leaves, let us say, in
the latter case, in the former the earth’s interposition. For, one
might argue, if this cause is not present, these phenomena will
have some other cause: if it is present, its effect will be at once
implied by it-the eclipse by the earth’s interposition, the fall of
the leaves by the possession of broad leaves; but if so, they will
be logically coincident and each capable of proof through the
other. Let me illustrate: Let A be deciduous character, B the
possession of broad leaves, C vine. Now if A inheres in B (for
every broad-leaved plant is deciduous), and B in C (every vine
possessing broad leaves); then A inheres in C (every vine is
deciduous), and the middle term B is the cause. But we can also
demonstrate that the vine has broad leaves because it is deciduous.
Thus, let D be broad-leaved, E deciduous, F vine. Then E inheres in
F (since every vine is deciduous), and D in E (for every deciduous
plant has broad leaves): therefore every vine has broad leaves, and
the cause is its deciduous character. If, however, they cannot each
be the cause of the other (for cause is prior to effect, and the
earth’s interposition is the cause of the moon’s eclipse and not
the eclipse of the interposition)-if, then, demonstration through
the cause