The Complete Aristotle (eng.)

statement contrary to it, or by quoting previous decisions.
    1. By ‘attacking your opponent’s own statement’ I mean, for
instance, this: if his enthymeme should assert that love is always
good, the objection can be brought in two ways, either by making
the general statement that ‘all want is an evil’, or by making the
particular one that there would be no talk of ‘Caunian love’ if
there were not evil loves as well as good ones.
    2. An objection ‘from a contrary statement’ is raised when, for
instance, the opponent’s enthymeme having concluded that a good man
does good to all his friends, you object, ‘That proves nothing, for
a bad man does not do evil to all his friends’.
    3. An example of an objection ‘from a like statement’ is, the
enthymeme having shown that ill-used men always hate their
ill-users, to reply, ‘That proves nothing, for well-used men do not
always love those who used them well’.
    4. The ‘decisions’ mentioned are those proceeding from
well-known men; for instance, if the enthymeme employed has
concluded that ‘that allowance ought to be made for drunken
offenders, since they did not know what they were doing’, the
objection will be, ‘Pittacus, then, deserves no approval, or he
would not have prescribed specially severe penalties for offences
due to drunkenness’.
    Enthymemes are based upon one or other of four kinds of alleged
fact: (1) Probabilities, (2) Examples, (3) Infallible Signs, (4)
Ordinary Signs. (1) Enthymemes based upon Probabilities are those
which argue from what is, or is supposed to be, usually true. (2)
Enthymemes based upon Example are those which proceed by induction
from one or more similar cases, arrive at a general proposition,
and then argue deductively to a particular inference. (3)
Enthymemes based upon Infallible Signs are those which argue from
the inevitable and invariable. (4) Enthymemes based upon ordinary
Signs are those which argue from some universal or particular
proposition, true or false.
    Now (1) as a Probability is that which happens usually but not
always, Enthymemes founded upon Probabilities can, it is clear,
always be refuted by raising some objection. The refutation is not
always genuine: it may be spurious: for it consists in showing not
that your opponent’s premiss is not probable, but Only in showing
that it is not inevitably true. Hence it is always in defence
rather than in accusation that it is possible to gain an advantage
by using this fallacy. For the accuser uses probabilities to prove
his case: and to refute a conclusion as improbable is not the same
thing as to refute it as not inevitable. Any argument based upon
what usually happens is always open to objection: otherwise it
would not be a probability but an invariable and necessary truth.
But the judges think, if the refutation takes this form, either
that the accuser’s case is not probable or that they must not
decide it; which, as we said, is a false piece of reasoning. For
they ought to decide by considering not merely what must be true
but also what is likely to be true: this is, indeed, the meaning of
‘giving a verdict in accordance with one’s honest opinion’.
Therefore it is not enough for the defendant to refute the
accusation by proving that the charge is not hound to be true: he
must do so by showing that it is not likely to be true. For this
purpose his objection must state what is more usually true than the
statement attacked. It may do so in either of two ways: either in
respect of frequency or in respect of exactness. It will be most
convincing if it does so in both respects; for if the thing in
question both happens oftener as we represent it and happens more
as we represent it, the probability is particularly great.
    (2) Fallible Signs, and Enthymemes based upon them, can be
refuted even if the facts are correct, as was said at the outset.
For we have shown in the Analytics that no Fallible Sign can form
part of a valid logical proof.
    (3) Enthymemes depending on examples may be refuted in the same
way as probabilities. If we have a negative instance, the argument
is refuted, in so far as it is proved not inevitable, even though
the positive examples are more similar and more frequent. And if
the positive examples are more numerous and more frequent, we must
contend that the present case is dissimilar, or that its conditions
are dissimilar, or that it is different in some way or other.
    (4) It will be impossible to refute