The Complete Aristotle (eng.)

whether man has such and such a characteristic or not.
    Some combinations of predicates are such that the separate
predicates unite to form a single predicate. Let us consider under
what conditions this is and is not possible. We may either state in
two separate propositions that man is an animal and that man is a
biped, or we may combine the two, and state that man is an animal
with two feet. Similarly we may use ‘man’ and ‘white’ as separate
predicates, or unite them into one. Yet if a man is a shoemaker and
is also good, we cannot construct a composite proposition and say
that he is a good shoemaker. For if, whenever two separate
predicates truly belong to a subject, it follows that the predicate
resulting from their combination also truly belongs to the subject,
many absurd results ensue. For instance, a man is man and white.
Therefore, if predicates may always be combined, he is a white man.
Again, if the predicate ‘white’ belongs to him, then the
combination of that predicate with the former composite predicate
will be permissible. Thus it will be right to say that he is a
white man so on indefinitely. Or, again, we may combine the
predicates ‘musical’, ‘white’, and ‘walking’, and these may be
combined many times. Similarly we may say that Socrates is Socrates
and a man, and that therefore he is the man Socrates, or that
Socrates is a man and a biped, and that therefore he is a
two-footed man. Thus it is manifest that if man states
unconditionally that predicates can always be combined, many absurd
consequences ensue.
    We will now explain what ought to be laid down.
    Those predicates, and terms forming the subject of predication,
which are accidental either to the same subject or to one another,
do not combine to form a unity. Take the proposition ‘man is white
of complexion and musical’. Whiteness and being musical do not
coalesce to form a unity, for they belong only accidentally to the
same subject. Nor yet, if it were true to say that that which is
white is musical, would the terms ‘musical’ and ‘white’ form a
unity, for it is only incidentally that that which is musical is
white; the combination of the two will, therefore, not form a
unity.
    Thus, again, whereas, if a man is both good and a shoemaker, we
cannot combine the two propositions and say simply that he is a
good shoemaker, we are, at the same time, able to combine the
predicates ‘animal’ and ‘biped’ and say that a man is an animal
with two feet, for these predicates are not accidental.
    Those predicates, again, cannot form a unity, of which the one
is implicit in the other: thus we cannot combine the predicate
‘white’ again and again with that which already contains the notion
‘white’, nor is it right to call a man an animal-man or a
two-footed man; for the notions ‘animal’ and ‘biped’ are implicit
in the word ‘man’. On the other hand, it is possible to predicate a
term simply of any one instance, and to say that some one
particular man is a man or that some one white man is a white
man.
    Yet this is not always possible: indeed, when in the adjunct
there is some opposite which involves a contradiction, the
predication of the simple term is impossible. Thus it is not right
to call a dead man a man. When, however, this is not the case, it
is not impossible.
    Yet the facts of the case might rather be stated thus: when some
such opposite elements are present, resolution is never possible,
but when they are not present, resolution is nevertheless not
always possible. Take the proposition ‘Homer is so-and-so’, say ‘a
poet’; does it follow that Homer is, or does it not? The verb ‘is’
is here used of Homer only incidentally, the proposition being that
Homer is a poet, not that he is, in the independent sense of the
word.
    Thus, in the case of those predications which have within them
no contradiction when the nouns are expanded into definitions, and
wherein the predicates belong to the subject in their own proper
sense and not in any indirect way, the individual may be the
subject of the simple propositions as well as of the composite. But
in the case of that which is not, it is not true to say that
because it is the object of opinion, it is; for the opinion held
about it is that it is not, not that it is.
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    As these distinctions have been made, we must consider the
mutual relation of those affirmations and denials which assert or
deny possibility or contingency, impossibility