Transcript Syllogisms - english102-tamuc

Syllogisms
Formal Reasoning
Formal Reasoning
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Concerned with “form” or structures
Need have nothing to do with content
or fact
May use symbols (e.g., p, q, ζ, Þ)
Following form …
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As mentioned above, formal logic doesn’t
have to have anything to do with the real
world
“Validity” is about form, not fact
E.g.,
All heavenly bodies are made of milk
The sun is a heavenly body
The sun is made of milk
Deductive and Inductive
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Deductive
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No new information
Conclusions are certain
Inductive
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New information
Conclusions are probable
Formal reasoning is deductive
Syllogism
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Syn- together + logos, reason, discourse
Contains three (3) parts
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Major premise
Minor premise
Conclusion
Three (3) syllogistic types here considered:
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Categorical
Conditional
Disjunctive
Categorical Syllogism
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“All,” “None,” or “Some” syllogism
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Sound example
All freshmen are lazy
John is a freshman
John is lazy
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(major premise)
(minor premise)
(conclusion)
Faulty example
Some freshmen are lazy
John is a freshman
John is lazy
(maybe, maybe not)
Categorical Syllogism
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Better example of “some”
All girls like Jane Austen
Some students are girls
Some students like Jane Austen
(An unfounded generalization? You betcha.
But it’s formally correct.)
Conditional Syllogism
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“If-then” syllogism
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Antecedent
Consequent
E.g.,
If you go to school, you will learn something
You go to school
You will learn something
Conditional Syllogism
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Affirming the antecedent—saying the
“if” condition did in fact occur
If you go to school, you will learn something
You go to school
You will learn something
Conditional Syllogism
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Denying the consequent—saying the
“then” part did not occur
If you go to school, you will learn something
You did not learn something
You did not go to school
Conditional Syllogism
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Two (2) fallacies involved
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Denying the antecedent
Affirming the consequent
Denying the antecedent
If you go to school, you will learn something
You do not go to school
You will not learn anything
(Not necessarily! One may learn out of school)
Conditional Syllogism
Affirming the consequent
If you go to school, you will learn something
You learn something
You go to school
(Again, one may learn elsewhere)
Disjunctive Syllogism
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“Either-or” syllogism
Either you like Star Wars or Star Trek
You like Star Wars
You don’t like Star Trek
(Formally valid, but can’t we like both?)
Limitations
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Formal correctness insufficient to gain
adherence
Precise language essential to
analyzing and appraising arguments
Certainty cannot always be
established
Reasoning does not always follow
three-liner form
Sources Consulted
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Zarefsky, David. Argumentation: The
Study of Effective Reasoning. 2nd
Edition. The Great Courses. Chantilly,
VA: The Teaching Company, 2005.
Pirie, Madsen. How to Win Every
Argument: The Use and Abuse of
Logic. London: Continuum, 2006.