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For some things are peculiar to the species as distinct from the
genus； for species being distinct there must be attributes peculiar to
each。 Nor must we take as things which the superior term follows；
those things which the inferior term follows； e。g。 take as subjects of
the predicate 'animal' what are really subjects of the predicate
'man'。 It is necessary indeed； if animal follows man； that it should
follow all these also。 But these belong more properly to the choice of
what concerns man。 One must apprehend also normal consequents and
normal antecedents…； for propositions which obtain normally are
established syllogistically from premisses which obtain normally； some
if not all of them having this character of normality。 For the
conclusion of each syllogism resembles its principles。 We must not
however choose attributes which are consequent upon all the terms： for
no syllogism can be made out of such premisses。 The reason why this is
so will be clear in the sequel。
28
If men wish to establish something about some whole； they must
look to the subjects of that which is being established （the
subjects of which it happens to be asserted）； and the attributes which
follow that of which it is to be predicated。 For if any of these
subjects is the same as any of these attributes； the attribute
originally in question must belong to the subject originally in
question。 But if the purpose is to establish not a universal but a
particular proposition； they must look for the terms of which the
terms in question are predicable： for if any of these are identical；
the attribute in question must belong to some of the subject in
question。 Whenever the one term has to belong to none of the other；
one must look to the consequents of the subject； and to those
attributes which cannot possibly be present in the predicate in
question： or conversely to the attributes which cannot possibly be
present in the subject； and to the consequents of the predicate。 If
any members of these groups are identical； one of the terms in
question cannot possibly belong to any of the other。 For sometimes a
syllogism in the first figure results； sometimes a syllogism in the
second。 But if the object is to establish a particular negative
proposition； we must find antecedents of the subject in question and
attributes which cannot possibly belong to the predicate in
question。 If any members of these two groups are identical； it follows
that one of the terms in question does not belong to some of the
other。 Perhaps each of these statements will become clearer in the
following way。 Suppose the consequents of A are designated by B； the
antecedents of A by C； attributes which cannot possibly belong to A by
D。 Suppose again that the attributes of E are designated by F； the
antecedents of E by G； and attributes which cannot belong to E by H。
If then one of the Cs should be identical with one of the Fs； A must
belong to all E： for F belongs to all E； and A to all C；
consequently A belongs to all E。 If C and G are identical； A must
belong to some of the Es： for A follows C； and E follows all G。 If F
and D are identical； A will belong to none of the Es by a
prosyllogism： for since the negative proposition is convertible； and F
is identical with D； A will belong to none of the Fs； but F belongs to
all E。 Again； if B and H are identical； A will belong to none of the
Es： for B will belong to all A； but to no E： for it was assumed to
be identical with H； and H belonged to none of the Es。 If D and G
are identical； A will not belong to some of the Es： for it will not
belong to G； because it does not belong to D： but G falls under E：
consequently A will not belong to some of the Es。 If B is identical
with G； there will be a converted syllogism： for E will belong to
all A since B belongs to A and E to B （for B was found to be identical
with G）： but that A should belong to all E is not necessary； but it
must belong to some E because it is possible to convert the
universal statement into a particular。
It is clear then that in every proposition which requires proof we
must look to the aforesaid relations of the subject and predicate in
question： for all syllogisms proceed through these。 But if we are
seeking consequents and antecedents we must look for those which are
primary and most universal； e。g。 in reference to E we must look to
KF rather than to F alone； and in reference to A we must look to KC
rather than to C alone。 For if A belongs to KF； it belongs both to F
and to E： but if it does not follow KF； it may yet follow F。 Similarly
we must consider the antecedents of A itself： for if a term follows
the primary antecedents； it will follow those also which are
subordinate； but if it does not follow the former； it may yet follow
the latter。
It is clear too that the inquiry proceeds through the three terms
and the two premisses； and that all the syllogisms proceed through the
aforesaid figures。 For it is proved that A belongs to all E；
whenever an identical term is found among the Cs and Fs。 This will
be the middle term； A and E will be the extremes。 So the first
figure is formed。 And A will belong to some E； whenever C and G are
apprehended to be the same。 This is the last figure： for G becomes the
middle term。 And A will belong to no E； when D and F are identical。
Thus we have both the first figure and the middle figure； the first；
because A belongs to no F； since the negative statement is
convertible； and F belongs to all E： the middle figure because D
belongs to no A； and to all E。 And A will not belong to some E；
whenever D and G are identical。 This is the last figure： for A will
belong to no G； and E will belong to all G。 Clearly then all
syllogisms proceed through the aforesaid figures； and we must not
select consequents of all the terms； because no syllogism is
produced from them。 For （as we saw） it is not possible at all to
establish a proposition from consequents； and it is not possible to
refute by means of a consequent of both the terms in question： for the
middle term must belong to the one； and not belong to the other。
It is clear too that other methods of inquiry by selection of middle
terms are useless to produce a syllogism； e。g。 if the consequents of
the terms in question are identical； or if the antecedents of A are
identical with those attributes which cannot possibly belong to E；
or if those attributes are identical which cannot belong to either
term： for no syllogism is produced by means of these。 For if the
consequents are identical； e。g。 B and F； we have the middle figure
with both premisses affirmative： if the antecedents of A are identical
with attributes which cannot belong to E； e。g。 C with H； we have the
first figure with its minor premiss negative。 If attributes which
cannot belong to either term are identical； e。g。 C and H； both
premisses are negative； either in the first or in the middle figure。
But no syllogism is possible in this way。
It is evident too that we must find out which terms in this
inquiry are identical； not which are different or contrary； first
because the object of our investigation is the middle term； and the
middle term must be not diverse but identical。 Secondly； wherever it
happens that a syllogism results from taking contraries or terms which
cannot belong to the same thing； all arguments can be reduced to the
aforesaid moods； e。g。 if B and F are contraries or cannot belong to
the same thing。 For if these are taken； a syllogism will be formed
to prove that A belongs to none of the Es； not however from the
premisses taken but in the aforesaid mood。 For B will belong to all
A and to no E。 Consequently B must be identical with one of the Hs。
Again； if B and G cannot belong to the same thing； it follows that A
will not belong to some of the Es： for then too we shall have the
middle figure： for B will belong to all A and to no G。 Consequently
B must be identical with some of the Hs。 For the fact that B and G
cannot belong to the same thing differs in no way from the fact that B
is identical with some of the Hs： for that includes everything which
cannot belong to E。
It is clear then that from the inquiries taken by themselves no
syllogism results； but if B and F are contraries B must be identical
with one of the Hs； and the syllogism results through these terms。
It turns out then that those who inquire in this ma