Deductive and Inductive
Reasoning
F.O.A. (Bellwork)
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Turn to page 11 in your blue book.
Answer 12-15.
Key Terms…
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Deductive- an argument whose conclusion is
certain
Inductive- an argument whose conclusion is
likely
Premise- a reason offered as support for a
claim
Syllogism- a form of deductive reasoning
consisting of a major premise, a minor
premise, and a conclusion.
Deductive Reasoning
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Deductive Reasoning – A type of logic
in which one goes from a general
statement to a specific instance.
The classic example
All men are mortal. (major premise)
Socrates is a man. (minor premise)
Therefore, Socrates is mortal. (conclusion)
Deductive Reasoning
Examples:
1.
All students eat pizza.
Claire is a student at ASU.
Therefore, Claire eats pizza.
2. All athletes work out in the gym.
Barry Bonds is an athlete.
Therefore, Barry Bonds works out in the
gym.
Let’s try one…
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Smith owns only blue and brown pants.
Smith is wearing a pair of his pants today.
Therefore…
This is a deductive argument because the first two
premises prove the last sentence must be true.
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The soccer game is either on Thursday or
Friday.
I just found out that the game is not on
Thursday.
So the game must be on __________
Is this deductive?
Inductive Reasoning
Inductive Reasoning, involves going from
a series of specific cases to a general
statement. The conclusion in an
inductive argument is never guaranteed.
Example
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All men are messy.(–premise)
Mr. Southworth is a man.(– premise)
Therefore Mr. Southworth must be
messy. (--conclusion)
BUT NOT NECESSARILY!!! The argument is valid, but
certainly not true. It’s based on a false premise. Be
careful with false premises when using logic 
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January is cold in Siberia.
Today is January 14.
It will be another cold day in Siberia.
This argument is inductive. It is likely but
not guaranteed.
The local branch of Wachovia Bank was
robbed yesterday. Jenny needed money to
pay off her debts. She just bought a gun two
days ago, and I saw her hanging around the
local Wachovia bank yesterday morning.
Today the people she owed money to stopped
looking for her. So Jenny must have robbed
that bank.
If you have ever seen an episode of Law &
Order you know that they prove issues like
this to be wrong so this is _______ reasoning.
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Deductive (based on laws, rules, & things known):
All dogs are mammals. All mammals
have kidneys. Therefore, all dogs have
kidneys.
Inductive (based on an observation):
All dogs that we have seen are white;
therefore the next dog we see will be
white.
Deductive (based on facts, laws, rules):
All squares are rectangles and all
rectangles have four sides. So all squares
must have four sides.
Inductive (based on observations):
Since Chris is a good athlete, and there are
good athletes in his family. His sister
must be a good athlete, too.
Emily’s shirt is red. My’kia is wearing a
red shirt. Malik’s shirt is also red.
Therefore, the next person I see will be
wearing a red shirt.
According to the LMS discipline
policy, if a student is disrespectful to
a teacher, they receive a dean
referral. Anthony was disrespectful
to his teacher, so he will receive a
dean referral.
Women hate sports. Mrs.
Southworth is a woman.
She must hate sports.
Assignment
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Write down three inductive statements
and three deductive statements.
2
5
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7
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7
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2
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1
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8