Sigwart, indeed, has missed the essential difference between the
categorical and the hypothetical construction of syllogisms. In a
categorical syllogism of the first figure, the major premise, "Every M
whatever is P," is a universal, which we believe on account of previous
evidence without any condition about the thing signified by the subject
M, which we simply believe sometimes to be existent (e.g. "Every man
existent"), and sometimes not (e.g., "Every centaur conceivable"); and
the minor premise, "S is M," establishes no part of the major, but adds
the evidence of a particular not thought of in the major at all. But in
a hypothetical syllogism of the ordinary mixed type, the first or
hypothetical premise is a conditional belief, e.g. "If anything is M it
is P," containing a hypothetical antecedent, "If anything is M," which
is sometimes a hypothesis of existence (e.g. "If anything is an angel"),
and sometimes a hypothesis of fact (e.g. "If an existing man is wise");
and the second premise or assumption, "Something is M," establishes part
of the first, namely, the hypothetical antecedent, whether as regards
existence (e.g. "Something is an angel"), or as regards fact (e.g. "This
existing man is wise"). These very different relations of premises are
obliterated by Sigwart's false reduction of categorical universals to
hypotheticals. But even Sigwart's errors are outdone by Lotze, who not
only reduces "Every M is P" so "If S is M, S is P," but proceeds to
reduce this hypothetical to the disjunctive, "If S is M, S is P¹ or P²
or P³," and finds fault with the Aristotelian syllogism because it
contents itself with inferring "S is P" without showing what P. Now
there are occasions when we want to reason in this disjunctive manner,
to consider whether S is P¹ or P² or P³, and to conclude that "S is a
particular P"; but ordinarily all we want to know is that "S is P"; e.g.
in arithmetic, that 2 + 2 are 4, not any particular 4, and in life that
all our contemporaries must die, without enumerating all their
particular sorts of deaths. Lotze's mistake is the same as that of
Hamilton about the quantification of the predicate, and that of those
symbolists who held that reasoning ought always to exhaust all
alternatives by equations. It is the mistake of exaggerating exceptional
into normal forms of thought, and ignoring the principle that a rational
being thinks only to the point.
Public-domain text, read in full here on John Shaqi.
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