The Complete Aristotle (eng.)

without qualification, that the terms ought always to
be stated in the nominative, e.g. man, good, contraries, not in
oblique cases, e.g. of man, of a good, of contraries, but the
premisses ought to be understood with reference to the cases of
each term-either the dative, e.g. ‘equal to this’, or the genitive,
e.g. ‘double of this’, or the accusative, e.g. ‘that which strikes
or sees this’, or the nominative, e.g. ‘man is an animal’, or in
whatever other way the word falls in the premiss.
37
    The expressions ‘this belongs to that’ and ‘this holds true of
that’ must be understood in as many ways as there are different
categories, and these categories must be taken either with or
without qualification, and further as simple or compound: the same
holds good of the corresponding negative expressions. We must
consider these points and define them better.
38
    A term which is repeated in the premisses ought to be joined to
the first extreme, not to the middle. I mean for example that if a
syllogism should be made proving that there is knowledge of
justice, that it is good, the expression ‘that it is good’ (or ‘qua
good’) should be joined to the first term. Let A stand for
‘knowledge that it is good’, B for good, C for justice. It is true
to predicate A of B. For of the good there is knowledge that it is
good. Also it is true to predicate B of C. For justice is identical
with a good. In this way an analysis of the argument can be made.
But if the expression ‘that it is good’ were added to B, the
conclusion will not follow: for A will be true of B, but B will not
be true of C. For to predicate of justice the term ‘good that it is
good’ is false and not intelligible. Similarly if it should be
proved that the healthy is an object of knowledge qua good, of
goat-stag an object of knowledge qua not existing, or man
perishable qua an object of sense: in every case in which an
addition is made to the predicate, the addition must be joined to
the extreme.
    The position of the terms is not the same when something is
established without qualification and when it is qualified by some
attribute or condition, e.g. when the good is proved to be an
object of knowledge and when it is proved to be an object of
knowledge that it is good. If it has been proved to be an object of
knowledge without qualification, we must put as middle term ‘that
which is’, but if we add the qualification ‘that it is good’, the
middle term must be ‘that which is something’. Let A stand for
‘knowledge that it is something’, B stand for ‘something’, and C
stand for ‘good’. It is true to predicate A of B: for ex hypothesi
there is a science of that which is something, that it is
something. B too is true of C: for that which C represents is
something. Consequently A is true of C: there will then be
knowledge of the good, that it is good: for ex hypothesi the term
‘something’ indicates the thing’s special nature. But if ‘being’
were taken as middle and ‘being’ simply were joined to the extreme,
not ‘being something’, we should not have had a syllogism proving
that there is knowledge of the good, that it is good, but that it
is; e.g. let A stand for knowledge that it is, B for being, C for
good. Clearly then in syllogisms which are thus limited we must
take the terms in the way stated.
39
    We ought also to exchange terms which have the same value, word
for word, and phrase for phrase, and word and phrase, and always
take a word in preference to a phrase: for thus the setting out of
the terms will be easier. For example if it makes no difference
whether we say that the supposable is not the genus of the opinable
or that the opinable is not identical with a particular kind of
supposable (for what is meant is the same in both statements), it
is better to take as the terms the supposable and the opinable in
preference to the phrase suggested.
40
    Since the expressions ‘pleasure is good’ and ‘pleasure is the
good’ are not identical, we must not set out the terms in the same
way; but if the syllogism is to prove that pleasure is the good,
the term must be ‘the good’, but if the object is to prove that
pleasure is good, the term will be ‘good’. Similarly in all other
cases.
41
    It is not the same, either in fact or in speech, that A belongs
to all of that to which B belongs, and that A belongs to all of
that to all of which B belongs: for nothing prevents B from
belonging to