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

140
MEDIATE INFERENCE
Crusoe s footprint affords an example ; his perception of
it may be analysed thus :
"
This mark in the sand is a mark having such and
such qualities of size, shape, &c. ;
Every mark having these qualities is the imprint of
a man s foot ;
Therefore this mark in the sand is the imprint of
a man s foot."
"
The process by which the conclusion is reached passes
"
in a flash through the mind, in such cases ;
but none
the less it is a true syllogistic argument in fig. i.
The four moods of the first figure are known by the
names :
Barbara, Celarent, Darii, Ferio.
These names contain the vowels of the respective moods
in their proper order ; and the student will shortly see
this by no means exhausts their
"
connotation." Our
present object, however, is to discuss the special char
acteristics of these moods.
The mood Barbara is so familiar and constant a
mode of thought that its importance usually escapes
attention. But we might know beforehand the large
part that it must play in science ;
for science seeks for
results which are laws i.e., statements true universally
about certain kinds of fact. Every time we explain a
fact by the law i.e., find a new complete application
of the law we make a syllogism in Barbara, not for
mally, explicitly, or in expression, for this would make
the reasoning long and tedious ; but implicitly at every
step we reason, in such a case, in this form.
The following are examples of this mood, regarded as the
application of a law
When a material substance is heated, it expands ;
Glass is a material substance ;
. . Glass expands when heated.