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

324
FALLACIES.
conclusion are separated by various steps of inference,
a circulus in probando.
(b) The same type of fallacy is committed when we
take for granted a general principle which involves the
required conclusion, and which is just as much in need
of proof as the conclusion itself;
general
or, indeed, when any
truth is falsely taken to be self-evident. Mr
Welton quotes an example from Spencer s Education
(ch. i.)
"After stating that acquirement of every
kind has two values value as knowledge and value as
discipline Mr Spencer goes on to discuss the value of
different subjects from the point of view of knowledge.
He then turns to the disciplinary value of studies, and
commences his disquisition with the following flagrant
petitio : Having found what is best for the one end,
we have by implication found what is best for the other.
We may be quite sure that the acquirement of those
classes of facts which are most useful for regulating
conduct,
involves a mental exercise best fitted for
strengthening the faculties. It would be utterly con
trary to the beautiful economy of Nature, if one kind of
culture were needed for the gaining of information and
another kind were needed as a mental gymnastic.
(c) Aristotle says that if we assume the particulars to
prove the universal which involves them, we commit the
same kind of fallacy. This is induction per enumera-
tionem simplicem e.g., assuming that
warrants
"
"
some S is P
"
"
all S is P : it is an inductive fallacy.
(d) The fourth mode which Aristotle refers to is only
a more prolix form of the first. It is to prove a general
proposition by breaking it up into parts and assuming
the truth of each part.
(e) The fifth mode rests on immediate inference by
converse relation (ch. III. 12) : to assume, for instance,
"