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* REVIEW
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* Chapter 3: discussing 2 kinds of classical logical arguments:
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* deductive arguments
* conclusion is PROVED by the premises
* rigorous and inescapable, narrows the scope
* impossible to both ASSERT the premises AND
DENY the conclusion
* inductive arguments
* conclusion is PLAUSIBLE or LIKELY because of the
premises
* can be flawed, but widens the scope
* possible to assert the premises and deny the
conclusion (you can choose not to believe it)
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* REVIEW
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quick terminology reminders:
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* reminder: a conditional statement has the form:
if A, then B
...where A and B are statements.
* the A part is called the ANTECEDENT
* the B part is called the CONSEQUENT
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* reminder: a SYLLOGISM is a 3-statement argument,
with 2 premises and a conclusion
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* REVIEW
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* Some CLASSIC COMMON PATTERNS of DEDUCTIVE logic
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* modus ponens ("mode of AFFIRMATION")
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* PREMISES:
* If A, then B.
* A is true.
* CONCLUSION:
* Therefore, B is true.
* Also called "affirming the antecedent"
because A is the antecedent of a conditional 1st premise
and the 2nd premise asserts that A is true
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* modus tollens ("mode of DENIAL")
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* PREMISES:
* If A, then B.
* B is NOT true. (also: B is false)
* CONCLUSION:
* Therefore, A must NOT be true. (also: Therefore, A is false)
* Also called "Denying the Consequent" -- because B is the
consequent in the 1st premise, and the 2nd premise asserts
that B is false
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* Chain Argument
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* PREMISES:
* If A, then B.
* If B, then C.
* CONCLUSION:
* Therefore, if A, then C
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* REVIEW
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be careful, there ARE some NOT valid
classic deductive patterns:
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* NOT VALID: denying the antecedent
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* PREMISES:
* If A, then B.
* A is false.
* CONCLUSION:
* Therefore,...?
...no valid conclusion can be made about the value of B
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* NOT VALID: affirming the consequent
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* PREMISES:
* If A, then B.
* B is true.
* CONCLUSION:
* Therefore,...?
...no valid conclusion can be made about the value of A
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* END of REVIEW
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* there are some other classic syllogism forms:
* categorical - all, none, or some statements
* argument by elimination rules out possibilities
* mathmetical arguments
* argument from definition
* categorical syllogisms:
* arguments whose statements start with
"all", "none", "no", or "some"
* All oaks are trees.
All trees are plants.
Therefore... all oaks are plants.
* Some Democrats are elected officials.
All elected officials are politicians.
Therefore... some Democrats are politicians.
* argument by elimination:
* these rule out other possibilities to get to the
conclusion
(not limited to just two options -- see course text)
* Either his name is Joe or his name is David.
His name is not Joe.
Therefore... his name is David.
* Either Clara walked to the library or she drove.
But Clara did not drive to the library.
Therefore... Clara walked to the library
* mathematical argument
* use facts of mathematics to prove the conclusion
* 1 is less than 2.
2 is less than 3.
Therefore... 1 is less than 3.
* argument from definition
* uses definitions of the words in arguments to come to
a conclusion
* Devika is a cardiologist.
Definition: a cardiologist is a type of doctor
Therefore... Devika is a doctor.
* Bertha is an aunt.
Definition: an aunt is a female relative.
Therefore... Bertha is a female relative.
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* some classic INDUCTIVE patterns
* remember: inductive logic does not have the absolute,
inescapable nature of deductive logic;
BUT it can still be used to persuade
(and often involves "probablies"...)
* inductive generalization
* predictive argument
* argument from authority
* causal argument
* statistical argument
* argument by analogy
* inductive generalization:
* attribute some characteristics to most of or all members
of some given class
* All dinosaur bones found so far are over 65 million years
old.
Therefore, it is PROBABLY true that all dinosaur bones
are over 65 million years old.
* these claim that their conclusions are PROBABLE --
so, they tend to be inductive.
MORE on these on Wednesday!