To p i c 5
Inductive Arguments
“Logic takes care of itself;
all we have to do is to look
& see how it does it.”
- Ludwig Wittgenstein
Common Patterns of
Inductive Reasoning
Six common patterns,
Inductive generalization
Predictive argument
Argument from authority
Causal argument
Statistical argument
Argument from analogy
Of the six common patterns,
Inductive generalizations, by
definition, are always inductive.
Predictive arguments, arguments from
authority, causal arguments, statistical
arguments & arguments from analogy are
generally, but not always, inductive.
The causal argument below, for example, is deductive:
Whenever iron is exposed to oxygen, it rusts.
This iron pipe has been exposed to oxygen.
Therefore, it will rust.
Inductive Generalization (1/2)
common pattern
An argument in which a generalization
is claimed to be probably true.
based on information about some members of
a particular class. ►Uses “All, most”.
Konnichiwa!! We are
E xa m p l e 1
sooo hardworking!!!
I’ve met 4 Japanese people, & they
were hardworking. Therefore, probably,
most Japanese people are hardworking.
Inductive Generalization (2/2)
common pattern
Example 2
ALL dinosaur bones so far discovered
have been more than 65 million years old.
Therefore,
probably
ALL dinosaur bones
are more than
65 million years old.
Predictive Argument
common pattern
A prediction that is
defended with reasons .
Example
Amy always
come late to class.
So, probably, she’ll
come late today.
Argument from Authority
common pattern
Asserts a claim & then supports claim
by citing some presumed authority
or witness who has said claim is true.
Example
presumed authority???
“My friend told me that he
saw a ghost on the 23rd floor.
Therefore, maybe there
is a ghost on the 23rd floor.”
Causal Argument
common pattern
Asserts or denies something is
the cause of something else.
E xa m p l e s
I can’t log in the MMLS.
The server is probably down.
Rashid possibly isn’t allergic
to peanuts. I saw him eat a
bag of peanuts last week.
Statistical Argument
common pattern
Rests on statistical evidence.
Rely on percentage (e.g. 50%, 99%, etc).
E xa m p l e
70% of MMU students
drive to the MMU campus.
Rosie is an MMU student.
Most likely, she
drives to the MMU campus.
Air-Rosie
Argument from Analogy
common pattern
Conclusion is claimed to
depend on analogy
(a comparison of similarity )
between 2 or more things.
Basic logical pattern: These things
are similar in such-and-such ways.
Therefore, they’re probably
similar in some further way.
Both look alike
but same
worth???
Argument
from
Analogy
Example
Ali
May
Venu
~ Ali is a graduate of MMU University,
& he is bright, assertive & polite.
~ May is a graduate of MMU University,
& she is bright, assertive, & polite.
~ Venu is a graduate of MMU University.
~ Therefore, most likely (or probably),
Venu is bright, assertive, & polite.
Inductive Strength
Weak
Strong
Inductive Strength
Strong inductive argument:
conclusion follows probably
from the premises.
Example
Most models are thin & slim.
Susan is a model.
Probably, she is thin & slim.
Inductive Strength
Weak Inductive argument:
the conclusion is not probably true
even if the premises are true.
Example
All Malaysian PMs has been a man.
Therefore, probably, the next
Malaysian PM will be a woman.
Inductive Strength
Weak Inductive argument:
Or put another way: argument in which
premises, even if assumed to be true,
do NOT make conclusion probable.
E xa m p l e
60% of students at LimKokWing University are
Chinese. Mustafa Kemal, owner of Mustafa’s
Arabic Cafe, is a student at LimKokWing
University. So, Mustafa is probably Chinese.
Inductive Strength
Strong inductive argument can:
1. have false premises, & a
probably false conclusion
All previous PM has been
women.
. So, it is likely the next PM
will be a woman.
2. have true premises, & a
probably true conclusion.
No previous PM has been
a Malaccan.
So, the next PM likely will
not be a Malaccan.
3. have false premises, & a
probably true conclusion.
All previous PM has been
well-educated.
So, the next PM likely will
be well-educated.
Inductive Strength
Strong inductive argument
CANNOT??
have true premises, & a
probably false conclusion.
E xa m p l e
Answer: CANNOT!!
Argument
No previous PM has been a woman.
So, the next PM likely will be a woman. is Weak!!!
Inductive Strength
Weak Inductive arguments??
False premises, & probably false conclusion.
True premises, & probably true conclusion.
False premises, & probably true conclusion.
True premises, & probably false conclusion?
ALL the above CAN take place.
Inductive Strength
If Strong inductive argument & ALL
true premises  cogent argument
(good argument)
If Weak inductive argument, or has at
least 1 false premise or both
 uncogent argument
(bad argument)
Deductive
Arguments
logical??
Valid*
Invalid
(ALL are
unsound)
ALL
true
YES
premises??
Sound**
*Valid: constructed that if
premises jointly asserted,
conclusion cannot be denied
without contradiction.
Argument is well reasoned.
Inductive
NO
Arguments
Unsound
logical??
ALL true premises
Strong
**Sound: having no
defect, sensible, valid.
## Cogent:
convincing
or believable
because it is clear.
ALL
true
YES
premises??
Cogent ##
ALL true premises
Weak
(ALL are
uncogent)
NO
Uncogent
Revision: Hypothetical Syllogism
If A,
Antecedent
then B.
Consequent
A. Therefore B.
Affirming the
Antecedent ►Modus Ponens
B. Therefore A.
Affirming the
Consequent
Not A. Therefore Not B.
Denying the
Antecedent
Not B. Therefore Not A.
Denying the
Consequent
►Modus Tollens.
Revision: Sound / Unsound
What is the d i f fe r e n c e
between a sound argument &
an unsound argument?
Answer
A sound argument =
valid argument & ALL true premises
An unsound argument =
invalid argument or at least one or
more false premise (s)
Revision: Cogent / Uncogent
What is the d i f fe r e n c e
between a cogent argument &
an uncogent argument?
Answer
A cogent argument =
strong argument & ALL true premises
An uncogent argument =
weak argument or at least one or
more false premise (s)
Question: Deductive Reasoning 1
1. Which of the following options best describes the
argument below if all the premises are true?
Premise 1: “All fishes need to consume food.”
Premise 2: “A bird is not a fish.”
Conclusion: “So, a bird needs to consume food.”
A.
B.
C.
D.
A valid and sound deductive argument
A valid but unsound deductive argument
An invalid but sound deductive argument
An invalid and unsound deductive argument
Question: Deductive Reasoning 2
2. Which of the following options best describes the
argument below if all the premises are true?
Premise 1: “All road vehicles have wheels.”
Premise 2: “A tourist bus is a road vehicle.”
Conclusion: “It follows that a tourist bus has wheels.”
A.
B.
C.
D.
A valid and sound deductive argument
A valid but unsound deductive argument
An invalid but sound deductive argument
An invalid and unsound deductive argument
Question: Deductive Reasoning 3
3. Which of the following options best describes the
argument below if only premise 1 is true?
Premise 1: “All land mammals have hair on their bodies.”
Premise 2: “A chicken is a land mammal.”
Conclusion: “So, a chicken has hair on its body.”
A.
B.
C.
D.
A valid and sound deductive argument
A valid but unsound deductive argument
An invalid but sound deductive argument
An invalid and unsound deductive argument
Question: Inductive Reasoning 1
1. Which of the following options best describes the
argument below if only premise 2 is true?
Premise 1: “Most Malaysians live in Kuala Lumpur.”
Premise 2: “Mr. Johari is a Malaysian.”
Conclusion: “So, Mr. Johari likely lives in Kuala Lumpur.”
A.
B.
C.
D.
A strong and cogent inductive argument
A strong but uncogent inductive argument
A weak but cogent inductive argument
A weak and uncogent inductive argument
Question: Inductive Reasoning 2
2. Which of the following options best describes the
argument below if all the premises are true?
Premise 1: “Most Asians live in Asia.”
Premise 2: “Hartono is an Asian.”
Conclusion: “So, Hartono probably lives in America.”
A.
B.
C.
D.
A strong and cogent inductive argument
A strong but uncogent inductive argument
A weak but cogent inductive argument
A weak and uncogent inductive argument
Question: Inductive Reasoning 3
3. Which of the following options best describes the
argument below if all the premises are true?
Premise 1: “Most Japanese were born in Japan.”
Premise 2: “My friend Kumiko is a Japanese girl.”
Conclusion: “So, she was probably born in Japan.”
A.
B.
C.
D.
A strong and cogent inductive argument
A strong but uncogent inductive argument
A weak but cogent inductive argument
A weak and uncogent inductive argument