Intro to Logic:
Induction
Induction
• Using observations and
evidence to generate
reasonable conclusions
• You must make some
assumptions to arrive at a
conclusion
• Induction is inherently
uncertain
• Induction can be strong or
weak
Induction
• According to Logic,
knowledge is built upon
formulating and justifying
claims
• A claim is a statement you
want someone to believe is
true.
• To logically justify your
claim, you must provide
reasons your claim is true.
Types of Induction
• How to create to strong conclusions based on
observations:
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Use real world examples
Collect evidence
Cite experts and the evidence they collect
Create meaningful analogies
Calculate statistics
Measure data
Find appropriate correlations and determine
causation
Induction: Example
• Look at one or more cases
within a specific class and
reason that if these cases have
certain features then other (as
yet unknown) cases in that
class also have those features.
• Are democracies good? Well,
the US is a democracy and
we’re pretty awesome.
Belgium is a democracy and
that’s a pretty nice place.
Therefore, from those
examples, democracies are
good.
Tests of Example
• 1. Are there a sufficient number of
examples examined to support the claim?
• 2. Are the examples typical of the
category or class the arguer is
generalizing to?
• 3. Are negative examples sufficiently
accounted for in the argument?
• 4. Are the examples relevant to the claim
being advanced?
Example Example:
Bears are dangerous!
• 1. Are there a
sufficient number of
examples examined
to support the claim?
• 2. Are the examples
typical of the
category or class the
arguer is
generalizing to?
• 3. Are negative
examples sufficiently
accounted for in the
argument?
• 4. Are the examples
relevant to the claim
being advanced?
• 1. How many bear attacks this
year would be enough to
determine if bears are
dangerous?
• 2. Are all attacks the same?
Should provoking a bear into
an attack be counted the same
as an unprovoked one?
• 3. How many bear encounters
are there with no attacks?
What encounter : attack ratio
would be convincing?
• 4. Are we sure that it was a
bear attack and not just a giant
dog? Was the Bear infected
with rabies?
Induction: Analogy
• Looks at similarities
between cases and
compares their basic,
essential features. If the
compared cases are alike
in essential traits, it’s
assumed that they will be
alike with traits that are
known in one case but not
known in the other.
• The difference between
an argument by example
and an argument by
analogy is argument by
example looks at one
characteristic within
many cases; argument by
analogy examines many
traits within two cases.
Samples of Analogy
• National health care in Canada, Britain,
France, and other countries are an effective
way to ensure all citizens have access to
medical health care. The system would be
effective in the U.S.
• Prohibition of alcohol was a disaster in the
1920s, prohibiting marijuana is a disaster in
the 21st century.
• In successful businesses, customer service
comes first. It’s time for teachers to begin
thinking of students and parents as customers
of the school.
Tests of Analogy
1. Are the compared cases alike in all
essential characteristics?
2. Are the compared characteristics
accurate?
3. Are the points of difference in the
compared cases significant?
Analogy Example:
Socialized Health Care in the US
 1. Are the compared
cases alike in all
essential
characteristics?
 2. Are the compared
characteristics
accurate?
 3. Are the points of
difference in the
compared cases
significant?
• 1. Are Canadians and American
health care needs similar? Are
their health providers similar? Do
the countries operate in a similar
way?
• 2. Is the data supporting the
Canadian system accurate? Is the
US data accurate? Are the
outcomes similar already?
• 3. Are the drawbacks of Canada’s
system substantially worse than
the benefits? Are the benefits of
America’s system better than its
shortcomings?
Induction: Causal Correlation
 Looks at specific
cases, classes of
cases, or both to
identify a
relationship or a
correlation
between them.
 Social Security
reduced poverty
rates among
senior citizens.
Tests of causal correlation
1. Is the link between cause and effect
consistent across populations, samples,
etc.?
2. Is the association of cause and effect
strong?
3. Does the movement of cause to effect
follow a regular and predictable
sequence?
Induction: Authority
•
Relies on the credibility of the
source to prove the claim.
•
Ninety-seven percent of climate
scientists agree that climatewarming trends over the past
century are very likely due to
human activities, and most of the
leading scientific organizations
worldwide have issued public
statements endorsing this position.
•
Tests of Authority
• 1. What are the credentials of the
authority? Are they related to the topic?
• 2. Does the authority relatively free from
bias?
• 3. Is the authority a reluctant witness?
• 4. Is the authority’s testimony consistent?
• 5. Does the argument rest primarily on
opinionated authority?
Induction: Statistics
• A mathematical way to
show a relationship
between issues (like
causal correlation). Using
statistics often enhances
the credibility of the
person making the
argument by providing
precise data for the
claims she is making.
Samples of Argument from Statistics
 Going to college makes you more
money.
Tests for Statistics
 1. Is the source of the
statistic valid?
 2. Is the statistic recent?
 3. Were the statistics
gathered carefully? (What
is the sample size of the
statistics, how were the
numbers reported or
gathered?)
 4. Are the statistics
consistent with other
data?
Conclusion
•
In order to make the best kinds of arguments, it is wise to use multiple
methods of induction to strengthen the conclusion.
Example
Authority
Strong
Conclusion
Statistics
Analogy
Causal Correlation
Strong Conclusion Example
Claim: Global Warming is Real and Caused by Humans
•
Example: Venus is an example of
CO2-induced global warming
•
Analogy: The Earth’s atmosphere
is like a greenhouse. The more
CO2 in the greenhouse, the
warmer it gets.
•
Causal Correlation: The measured
increase in CO2 emissions
correlates with the measured rise
in temps.
•
Authority: Scientists say so
•
Statistics: CO2 levels have
exceeded 400 ppm, the highest
ever recorded. Temps are also at
record highs.
Strong Conclusion Example
Claim: Global Warming is Real and Caused by Humans
•
Argument by Example:
•
“Venus very likely underwent a
runaway or ‘moist’ greenhouse phase
earlier in its history, and today is kept
hot by a dense CO2 atmosphere.” –
Chris Colose, April 2011
•
Columbia University, NASA
Atmosphere: 96% CO2
Surface Temp: 863 F
Strong Conclusion Example
Claim: Global Warming is Real and Caused by Humans
•
Argument by Analogy:
•
Whereas Venus is an example of how the runaway greenhouse effect can happen on a
planetary body as CO2 concentrations increase. Humans certainly did not do it to Venus.
•
The analogy here is that the Earth (and Venus) act like greenhouses. They absorb heat
energy as their CO2 levels rise.
Strong Conclusion Example
Claim: Global Warming is Real and Caused by Humans
Causal Correlation: The measured increase in CO2 emissions correlates with the
measured rise in temps.
Strong Conclusion Example
Claim: Global Warming is Real and Caused by Humans
Causal Correlation: The measured increase in CO2 emissions correlates with the
measured rise in temps.
Strong Conclusion Example
Claim: Global Warming is Real and Caused by Humans
Strong Conclusion Example
Claim: Global Warming is Real and Caused by Humans
•
Statistics: CO2 levels have
exceeded 400 ppm, the
highest ever recorded.
•
Temps are also at record
highs.
•
Extreme Weather is at an
all time high:
•
Heat Waves
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Drought
•
Cold Snaps
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Floods
•
Storms
•
Outbreaks
•
Fires
Conclusion continued
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It is impossible to “prove” an
inductive argument.
Induction is the basis of the
Scientific Method:
• Ask question
THAT DOESN’T MEAN THE
ARGUMENT ISN’T TRUE AND/OR
FACTUAL
• Form Hypothesis
For example, some people have
survived executions. Just because
there are exceptions doesn’t mean
that executions aren’t killing
people.
• Observe data
• Develop experiment
• Formulate conclusion
• Refine hypothesis
• Refine experiment
• And on and on and on
Conclusion continued
Inductive experiments
that repeatedly show
the same results will
eventually become a
THEORY:
“A well-confirmed type
of explanation of
nature” capable of
being supported or
falsified.
Examples of Major Theories:
• Plate Tectonics
• General Relativity
• Evolution
• Quantum Mechanics
• Big Bang
• Atomic Theory
• Germ Theory
• Gravity
Some people want to deceive you by
disguising their bad arguments as “logical.”
Why?