Transcript Categorical Syllogisms

Ch. 4
DEDUCTIVE ARGUMENT
Reasoning from the General to
the Specific
Deductive Argument
• A specific conclusion is inferred from a
series of generalized statements.
• Conclusions are usually indisputable
vs. Inductive Argument (ch3)
• A general conclusion was inferred from
several pieces of information
• Conclusions could contain factors of
uncertainty
Syllogism
• The most common way of presenting a
deductive argument (not found in inductive
arguments)
• Contains a major premise, a minor
premise, and a conclusion
Categorical Syllogism (Valid)
• Major Premise
• Minor Premise
• Conclusion
All A is B.
C is A,
C is B.
Categorical Syllogism example
MAJ: All students in Critical Thinking are nice.
A
is/are
B)
MIN: Katie is a student in Critical Thinking.
(C
is
CON: Katie is nice.
(C
is B)
A)
Another way of looking at it.
C. Katie
A. Students
in Critical Thinking
B. Nice People
Another example
Major Premise: All WHS students (A) are to
be in class at 7:25 AM (B).
Minor Premise: Josh (C) is a WHS student
(A).
Conclusion: Josh (C) is be in class at 7:25
AM (B).
What would the diagram look like?
__________________
__________________
__________________
Answer
C. Josh
A. WHS students
B. People who must
be at school at 7:25
Notice the difference in this one
• Major Premise: *Most people between the
ages of 16 and 18 (A) are students (B)
• Minor Premise: Christina (C) is 18 years
old (A)
• Conclusion: Christina (C) is *probably a
student (B).
*be aware of overstatement
The diagram
• The diagram must change to reflect the
syllogism correctly.
B. Students
A. 16-18 yr
olds (remember
most, not all)
C. Christina
Incorrect/Untruthful Conclusion
• Major Premise: All students (A) are lazy,
ignorant individuals (B).
• Minor Premise: Ryan (C) is a student (A)
• Conclusion: Ryan (C) is a lazy and
ignorant individual (B)
• Valid in form, but false premise.
Incorrect/Untruthful Conclusion
• Appears valid in form;
however, incorrect
conclusion.
• False major premise
C. Ryan
A. All
Students
B. Lazy,
Ignorant
People
Incorrect/Untruthful Conclusion
• If the premise(s) is false, the conclusion
will be untrue.
• Use the Tests of Evidence from ch. 2 to
determine the truth of the premises.
– Sufficient evidence?
– Evidence deliberately omitted?
– Conflict with other evidence?
– Relevant evidence?
– Accurately reported evidence?
INVALID Categorical Syllogisms
• Major Premise:
• Minor Premise:
• Conclusion:
• Invalid in form
All A is B.
C is B.
C is A.
INVALID example
• Major Premise: All basketball players (A)
are good runners (B).
• Minor Premise: Mike (C) is a good runner
(B).
• Conclusion: Mike (C) is a basketball
player (A).
The Diagram
Mike is a good runner, but that doesn’t mean
he is a b-ball player.
A. BB Players
C. Mike
B. Good
runners
Enthymeme
• A Catagorical syllogism with an unstated
premise
– contains conclusion
– Missing a premise
• Note: Enthymemes are always
considered valid!!
Enthymeme example
• These jeans are sure to be in style
because they were purchased from the
Gap.
– Major Premise (unstated): Most jeans
purchased from the Gap are in style.
– Minor Premise: These jeans were purchased
from the Gap.
– Conclusion: These jeans are (probably) in
style.
In Conclusion: Differences between
inductive & deductive reasoning
1. Arguments using inductive reasoning go
from specific to general, and it is difficult
to arrive at an indisputable conclusion.
2. Deductive reasoning can produce logical
conclusions if (a) the syllogism is
correctly structured. (b)the premises
satisfy the Tests of Evidence