An introductory text-book of logic - Mellone, Sydney - Rare Books at ...

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FALLACIES.
not an argument at all, but an appeal to physical
force.
(4) The fallacy of the Consequent is vaguely ex
plained in some modern text-books as meaning "any
kind of loose or inconsequent argument," and described
by the phrase non sequitur.
Aristotle meant by it
from the affirmation of
simply the invalid "argument
the in a consequent" hypothetical proposition. He
mentions cases of it in arguments from presumptive
evidence e.g.,
"This man has no visible means of
support, and must therefore be a professional thief."
Even if we grant that
"
if a man is a professional thief,
he will have no visible means of support," the particular
conclusion will not follow. Of equal importance, as
we have seen (ch. VII. 3), is the fallacy of denying the
antecedent. When long pieces of reasoning are being
dealt with, the
the form of assuming
"
"
denial of the antecedent
supported by invalid arguments,
often takes
that because the conclusion is
it is false.
(5) The fallacy of Petitio Principii (TO ev apXV
alrdaOai /cal \a/mftdveiv) i.e., to assume the con
clusion which is to be proved. 1
may take place in five ways.
Aristotle says that this
(a) To assume the proposition which is to be proved,
and in the very form in which it is to be proved. As
Aristotle hints, this is hardly possible unless the as
sumption is concealed by some sort of verbal confusion.
An illustration of it is to be found in Mill s account of
the ground of the axiom which lies at the basis of
Induction the Uniformity of Nature. This principle,
says Mill, is the "ultimate major premise
of all In-
1 Petitio principii does not really translate Aristotle s r6 eV
diTer0ai, which means petitio quasiti or assumption of the con
clusion, as we have said.