The Complete Aristotle (eng.)

a proof of
the contradictory. If, then, there is no proof as regards an
accident of anything, there is no refutation. For supposing, when A
and B are, C must necessarily be, and C is white, there is no
necessity for it to be white on account of the syllogism. So, if
the triangle has its angles equal to two right-angles, and it
happens to be a figure, or the simplest element or starting point,
it is not because it is a figure or a starting point or simplest
element that it has this character. For the demonstration proves
the point about it not qua figure or qua simplest element, but qua
triangle. Likewise also in other cases. If, then, refutation is a
proof, an argument which argued per accidens could not be a
refutation. It is, however, just in this that the experts and men
of science generally suffer refutation at the hand of the
unscientific: for the latter meet the scientists with reasonings
constituted per accidens; and the scientists for lack of the power
to draw distinctions either say ‘Yes’ to their questions, or else
people suppose them to have said ‘Yes’, although they have not.
    Those that depend upon whether something is said in a certain
respect only or said absolutely, are clear cases of ignoratio
elenchi because the affirmation and the denial are not concerned
with the same point. For of ‘white in a certain respect’ the
negation is ‘not white in a certain respect’, while of ‘white
absolutely’ it is ‘not white, absolutely’. If, then, a man treats
the admission that a thing is ‘white in a certain respect’ as
though it were said to be white absolutely, he does not effect a
refutation, but merely appears to do so owing to ignorance of what
refutation is.
    The clearest cases of all, however, are those that were
previously described’ as depending upon the definition of a
‘refutation’: and this is also why they were called by that name.
For the appearance of a refutation is produced because of the
omission in the definition, and if we divide fallacies in the above
manner, we ought to set ‘Defective definition’ as a common mark
upon them all.
    Those that depend upon the assumption of the original point and
upon stating as the cause what is not the cause, are clearly shown
to be cases of ignoratio elenchi through the definition thereof.
For the conclusion ought to come about ‘because these things are
so’, and this does not happen where the premisses are not causes of
it: and again it should come about without taking into account the
original point, and this is not the case with those arguments which
depend upon begging the original point.
    Those that depend upon the assumption of the original point and
upon stating as the cause what is not the cause, are clearly shown
to be cases of ignoratio elenchi through the definition thereof.
For the conclusion ought to come about ‘because these things are
so’, and this does not happen where the premisses are not causes of
it: and again it should come about without taking into account the
original point, and this is not the case with those arguments which
depend upon begging the original point.
    Those that depend upon the consequent are a branch of Accident:
for the consequent is an accident, only it differs from the
accident in this, that you may secure an admission of the accident
in the case of one thing only (e.g. the identity of a yellow thing
and honey and of a white thing and swan), whereas the consequent
always involves more than one thing: for we claim that things that
are the same as one and the same thing are also the same as one
another, and this is the ground of a refutation dependent on the
consequent. It is, however, not always true, e.g. suppose that and
B are the same as C per accidens; for both ‘snow’ and the ‘swan’
are the same as something white’. Or again, as in Melissus’
argument, a man assumes that to ‘have been generated’ and to ‘have
a beginning’ are the same thing, or to ‘become equal’ and to
‘assume the same magnitude’. For because what has been generated
has a beginning, he claims also that what has a beginning has been
generated, and argues as though both what has been generated and
what is finite were the same because each has a beginning. Likewise
also in the case of things that are made equal he assumes that if
things that assume one and the same magnitude become equal, then
also things that become equal assume one magnitude: i.e. he assumes
the consequent. Inasmuch,