Induction is the process of reasoning from facts or
instances and arriving at a general claim.
Situation: You go to an Arizona
Vehicle Center to renew your driver’s license.
You stand in line two hours to get your document.
Later you return for new license plates; clerk gives you
wrong advice; you stand in line three hours.
A third time you go there in response to a letter asking for
information, and you discover that you need your car
registration form, but the letter failed to tell you.
You conclude that the AZ Motor Vehicle Center is
You have arrived at this conclusion by induction.
Deductive reasoning moves from the
general to the specific.
Several visits to the AZ Motor Vehicle Center were
They convince you that the AZ Motor Vehicle
Center cares little about the convenience of its
You will not be happy the next time you must
Using Deductive Reasoning
Deductive reasoning might
go something like this:
• The AZ Motor Vehicle
Center wastes people’s
• I have to go to the AZ
Motor Vehicle Center
• Therefore, tomorrow my
time will be wasted.
You reached this conclusion by means of deduction.
• Deductive arguments have
parts: two premises and a
• This three-part
structure is known as a
• The argument is valid when
the conclusion LOGICALLY
follows the premises.
Valid and Invalid Reasoning
The following argument is valid:
Premise 1 When it snows, the streets
get wet. (fact)
Premise 2 It is snowing (fact)
Conclusion Therefore, the streets are wet.
The following argument is invalid:
Premise 1 When is snows, the streets
get wet. (fact)
Premise 2 The streets are wet.
Conclusion Therefore, it is snowing.
The invalid argument has acceptable premises because the
premises are facts. The argument’s conclusion is wrong. It
ignores other reasons why the streets may be wet.
Valid and Invalid Arguments
Why is the following invalid?
Premise 1 When the battery is
dead, a car will not start.
Premise 2 My car will not start.
Conclusion My battery is dead.
Why is the Following Valid?
Premise 1: When unemployment
rates rise, an economic recession
Premise 2: The unemployment has
Conclusion: An economic recession
The argument is valid. The writer of
the argument must support the
claim that the first premise is
Argument begins With specific
With a general
With a general
With a specific
Conclusion is Reliable or
True or false
Reasoning is used To discover
To apply what is
Comparison of Inductive and Deductive Reasoning
Recognizing and Avoiding Logical
Logical fallacies are flaws
that lead to illogical statements
That SEEM logical.
They masquerade as reasonable
They manipulate readers by
appealing to their emotions.
Most logical fallacies are known by
labels to indicate where reasoning
has gone wrong in the thinking
• Hasty generalization—when someone
generalizes from inadequate evidence.
• “My hometown is the best place to live in the
state” - - generalization is hasty with only two
examples of why it is pleasant.
• Stereotyping—a type of generalization that
occurs if when someone makes prejudiced,
sweeping claims about all members of a
• Sexism—a type of generalization that occurs
when someone discriminates based on sex.
occurs when two
premises are used
• “Only when
destroyed us will
we be convinced
of the need to
Guilt by association
• Guilt by association implies
that an individual’s
argument, ideas, or opinions
lack merit because of that
person’s activities, interest, or
• “Matilda, who is running for
mayor, belongs to
International Hill Climbers
• Ignores evidence on the other side of a question.
• Television commercials use this strategy.
When three slim, happy customers rave about a new
diet plan, they do not mention that
a) the plan does not work for everyone and
b) other plans work better for some people.
The makers of the commercial select evidence to
promote their cause.
Taking Something Out of Context
• Taking something out of context
separates an idea or fact from the
material surrounding it, thus
distorting it for special purposes.
• A movie critic writes: “The plot was
predictable and boring but the
music was sparkling.”
• The advertisement for the movie
says, “Critic calls this movie
Appeal to Ignorance
• Appeal to ignorance assumes that
the argument is valid simply
because it has not been shown to
• Appeals to ignorance can be very
persuasive because they prey on
people’s lack of knowledge.
• “Since no one has proven that
depression does not cause cancer,
we can assume it does.”
• The absence of opposing evidence
Ambiguity describes expressions that
are not clear because they have more
than one meaning.
An ambiguous expression may be
taken either way by the reader.
A statement such as “They were
entertaining guests” is ambiguous.
Were the guests humorous or were
people giving hospitality to guests?
A Complex or Loaded Question
• A complex question contains one or
more unproven assumptions.
• “Are you still spending time with
known drug addicts?”
Appeal to the People
• Appeal to the people draws
on whatever the people hold
dear—for example, country,
• This approach tries to sway
people by using a favorable
label instead of sound
• “A vote for Richard
Williams is a vote
for the flag.”
• Name calling attaches
an unpleasant label to
something or someone.
• Name-calling can stop
readers from thinking.
• “Gertrude Jones was once
an alcoholic, so she
cannot possibly say
anything of value about
Think and Write Logically
• Explain how your evidence is
• Discuss the connection between
facts and the inferences they
• You must guide your readers and
not let them be fooled by confusing
or false data.