A Class Room Logic: Deductive and Inductive, with Special Application to the Science and Art of TeachingMcNair, George Hastings
Philosophy
A Class Room Logic: Deductive and Inductive, with Special Application to the Science and Art of Teaching
McNair, George Hastings
Logic
This is complex because there are two antecedents as well as two
consequents, and destructive because the conclusion is negative.
Briefly: (1) A simple dilemma is one where either the antecedent or
consequent is repeated; whereas if neither is repeated the dilemma is
complex. (2) A constructive dilemma contains an affirmative conclusion;
while a destructive dilemma uses a negative conclusion. (3) A simple
dilemma has as its conclusion a categorical proposition; whereas the
conclusion of a complex dilemma is always disjunctive.
If the number of antecedents and consequents be increased, a trilemma,
tetralemma, etc., may result.
ILLUSTRATION――_Trilemma._
If A is B, W is X; and if C is D, Y is Z; and if E is F, U is V,
But either A is B, or C is D, or E is F,
Hence either W is X, or Y is Z, or U is V.
Some authorities define a dilemma as a syllogism in which the
“major-hypothetical” has _more than one antecedent_ while the “minor”
must be disjunctive. This viewpoint necessarily _excludes_ the second
form or the simple destructive dilemma. The weight of authority,
however, appears to favor the classification here recommended.
=15. THE ONE RULE INVOLVED IN DILEMMATIC ARGUMENTS.=
Since the major premise of the dilemma is hypothetical, the rule for
testing such would of necessity be the hypothetical rule; namely, “The
minor premise must either affirm the antecedent or deny the consequent.”
As this rule and the fallacies incident to it have been treated in
detail, further discussion is unnecessary.
=16. ILLUSTRATIVE EXERCISE TESTING DISJUNCTIVE AND DILEMMATIC
ARGUMENTS.=
(1) If the arithmetic contains useful facts, it will help to good
citizenship; and if it trains the powers of reason, it will
help to good citizenship,
But the arithmetic either contains useful facts or trains the
powers of reason,
Hence it will help to good citizenship.
This is a simple constructive dilemma in which the minor premise
affirms the antecedents. The argument is, therefore, valid since it
conforms to the rules of the hypothetical syllogism. The fact that the
minor premise may not be a perfect disjunctive does not invalidate the
conclusion, inasmuch as it is perfectly obvious that if the arithmetic
fulfilled both the requirements of the antecedents, the conclusion
would still obtain. It may, therefore, be inferred that if the dilemma
conforms to the rules of the hypothetical argument, it is valid, though
the disjunctive proposition which it contains may not be strictly
logical.
(2) A man is either temperate or intemperate; and, as I have seen you
drunk several times, I conclude that you are intemperate.
_Arranged logically._
A man is either temperate or intemperate,
You are not temperate,
∴ You are intemperate.
Public-domain text, read in full here on John Shaqi.
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