A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. I
John Stuart Mill · en
Though all ratiocination admits of being thrown into one or the other of
these forms, and sometimes gains considerably by the transformation,
both in clearness and in the obviousness of its consequence; there are,
no doubt, cases in which the argument falls more naturally into one of
the other three figures, and in which its conclusiveness is more
apparent at the first glance in those figures, than when reduced to the
first. Thus, if the proposition were that pagans may be virtuous, and
the evidence to prove it were the example of Aristides; a syllogism in
the third figure,
Aristides was virtuous,
Aristides was a pagan,
therefore
Some pagan was virtuous,
would be a more natural mode of stating the argument, and would carry
conviction more instantly home, than the same ratiocination strained
into the first figure, thus--
Aristides was virtuous,
Some pagan was Aristides,
therefore
Some pagan was virtuous.
A German philosopher, Lambert, whose _Neues Organon_ (published in the
year 1764) contains among other things one of the most elaborate and
complete expositions which had ever been made of the syllogistic
doctrine, has expressly examined what sort of arguments fall most
naturally and suitably into each of the four figures; and his
investigation is characterized by great ingenuity and clearness of
thought.[3] The argument, however, is one and the same, in whichever
figure it is expressed; since, as we have already seen, the premises of
a syllogism in the second, third, or fourth figure, and those of the
syllogism in the first figure to which it may be reduced, are the same
premises in everything except language, or, at least, as much of them as
contributes to the proof of the conclusion is the same. We are
therefore at liberty, in conformity with the general opinion of
logicians, to consider the two elementary forms of the first figure as
the universal types of all correct ratiocination; the one, when the
conclusion to be proved is affirmative, the other, when it is negative;
even though certain arguments may have a tendency to clothe themselves
in the forms of the second, third, and fourth figures; which, however,
cannot possibly happen with the only class of arguments which are of
first-rate scientific importance, those in which the conclusion is an
universal affirmative, such conclusions being susceptible of proof in
the first figure alone.[4]