Logic and Critical Thinking
Inductive Fallacies
2 criteria of a good sample
Is the sample large enough?
Is it representative?
2 criteria of a good sample
Is the sample large enough?
If not, then we have
the fallacy of small sample
Is it representative?
If not, then we have
the fallacy of biased sample
REASONING BY ANALOGY
A has properties x and y
B has properties x and y
A also has property z
B probably has property z as well
Fallacy of Questionable Analogy
occurs when there is an important difference
between the two things being compared.
Fallacy of Questionable Statistics
occurs when you have a good reason to believe
that the statistic is false or at least questionable
1. Faulty Method (e.g. small sample, biased
sample, lack of a random sample)
2. You’ve seen a contrary statistic somewhere else
3. The statistic can’t be reliably known
Questionable Use of Statistics
when the premises contain good statistics,
but the conclusion doesn’t follow from those
statistical premises.
“Three out of every four
dentists surveyed recommend
X to their patients.”
Causal Reasoning
effect to cause
cause to effect
The fallacy of questionable cause occurs
when you have a good reason to
believe that the cited cause is not the
correct one.
Post Hoc Fallacy
“Post hoc, ergo propter hoc.”
After this, therefore because of this.
Scientific Method
III. Scientific Method
1. define the issue
2. gather evidence
3. form hypothesis
4. test
5. evaluate (3 main options)
not looking for verification, but falsification
1. accept
2. reject and revise
(In a testing situation, if you reject, the next step is to REVISE)
3. or suspend judgment
Hasty Conclusion
jumping to a conclusion without enough evidence
Small Sample
This is a type of
hasty conclusion.
when the sample is not large enough