The Complete Aristotle (eng.)

happen of necessity or usually; for a chance event
happens neither of necessity nor usually. If the thing happens
usually, then even supposing his statement does not distinguish
whether he meant that it happens usually or that it happens
necessarily, it is open to you to discuss it on the assumption that
he meant that it happens necessarily: e.g. if he has stated without
any distinction that disinherited persons are bad, you may assume
in discussing it that he means that they are so necessarily.
    Moreover, look and see also if he has stated a thing to be an
accident of itself, taking it to be a different thing because it
has a different name, as Prodicus used to divide pleasures into joy
and delight and good cheer: for all these are names of the same
thing, to wit, Pleasure. If then any one says that joyfulness is an
accidental attribute of cheerfulness, he would be declaring it to
be an accidental attribute of itself.
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7
    Inasmuch as contraries can be conjoined with each other in six
ways, and four of these conjunctions constitute a contrariety, we
must grasp the subject of contraries, in order that it may help us
both in demolishing and in establishing a view. Well then, that the
modes of conjunction are six is clear: for either (1) each of the
contrary verbs will be conjoined to each of the contrary objects;
and this gives two modes: e.g. to do good to friends and to do evil
to enemies, or per contra to do evil to friends and to do good to
enemies. Or else (2) both verbs may be attached to one object; and
this too gives two modes, e.g. to do good to friends and to do evil
to friends, or to do good to enemies and to do evil to enemies. Or
(3) a single verb may be attached to both objects: and this also
gives two modes; e.g. to do good to friends and to do good to
enemies, or to do evil to friends and evil to enemies.
    The first two then of the aforesaid conjunctions do not
constitute any contrariety; for the doing of good to friends is not
contrary to the doing of evil to enemies: for both courses are
desirable and belong to the same disposition. Nor is the doing of
evil to friends contrary to the doing of good to enemies: for both
of these are objectionable and belong to the same disposition: and
one objectionable thing is not generally thought to be the contrary
of another, unless the one be an expression denoting an excess, and
the other an expression denoting a defect: for an excess is
generally thought to belong to the class of objectionable things,
and likewise also a defect. But the other four all constitute a
contrariety. For to do good to friends is contrary to the doing of
evil to friends: for it proceeds from the contrary disposition, and
the one is desirable, and the other objectionable. The case is the
same also in regard to the other conjunctions: for in each
combination the one course is desirable, and the other
objectionable, and the one belongs to a reasonable disposition and
the other to a bad. Clearly, then, from what has been said, the
same course has more than one contrary. For the doing of good to
friends has as its contrary both the doing of good to enemies and
the doing of evil to friends. Likewise, if we examine them in the
same way, we shall find that the contraries of each of the others
also are two in number. Select therefore whichever of the two
contraries is useful in attacking the thesis.
    Moreover, if the accident of a thing have a contrary, see
whether it belongs to the subject to which the accident in question
has been declared to belong: for if the latter belongs the former
could not belong; for it is impossible that contrary predicates
should belong at the same time to the same thing.
    Or again, look and see if anything has been said about
something, of such a kind that if it be true, contrary predicates
must necessarily belong to the thing: e.g. if he has said that the
‘Ideas’ exist in us. For then the result will be that they are both
in motion and at rest, and moreover that they are objects both of
sensation and of thought. For according to the views of those who
posit the existence of Ideas, those Ideas are at rest and are
objects of thought; while if they exist in us, it is impossible
that they should be unmoved: for when we move, it follows
necessarily that all that is in us moves with us as well. Clearly
also they are objects of sensation, if they exist in us: for it is
through the sensation of sight that we recognize the