fallacies - weak induction. homework review: fallacies » pp. 103-105, §4.1 “fallacies in...
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Homework
• Review:• Fallacies
» pp. 103-105, §4.1 “Fallacies in General”
» pp. 121-131, §4.3 “Fallacies of Weak Induction”
• Inductive Argumentation» Analogical Reasoning, e.g., ex. 8.4» Causal Argumentation, e.g., 8.3b» Inductive Generalization, e.g., 8.2b
• Read for Next Class– pp. 106-116, §4.2 “Fallacies of Relevance”
• Analysis– Identify Subject and Analogue
• Criticism1. Are common features relevantly similar to
inferred feature?
2. Is there a disanalogy?
Arguments from Analogy?
Both my dog and my neighbor's dog are well-loved members of the family. Each one is well fed, house broken, walked on a regular basis. My dog has a very calm temperament. So I infer that my neighbor's dog also has a calm temperament.
Kinds of Fallacies
a defect or error traceable to the very structure (or form) of the argument
a defect which can be detected only by reference to the content of an argument
vsForm ContentFormal Fallacies Informal Fallacies
Kinds of Informal Fallacies
Fallacies of:1. Relevance2. Weak Induction3. Presumption4. Ambiguity
a. Amphiboly/Equivocationb. Whole/Part
See pages 153f for a complete list
Only required to classify each
fallacy according to these four
types
Your Task on the ExamExplain how the argument is fallacious.
Fallacies on Exam
fallacy of relevancefallacy of weak inductionfallacy of presumptionfallacy of ambiguitynone of the above
Weak Induction
• Inferential connection – evidence not strong enough to support conclusion• Premises are relevant to conclusion• Premises do not warrant conclusion
The Five Fallacies of Weak Induction
1. Appeal to Ignorance2. Appeal to Unqualified Authority3. Hasty Generalization4. False Cause5. Weak Analogy
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
1. Appeal to Ignorance2. Appeal to Unqualified Authority3. Hasty Generalization4. False Cause5. Weak Analogy
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
See earlier presentations for assessment criteria
The Five Fallacies of Weak Induction
1. Appeal to Ignorance– Smoking has not been proven to cause cancer,
therefore tobacco products are not carcinogenic • Premises offer only a lack of evidence• A definite assertion is made on this basis
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
Exceptions1. If search for evidence has been (seemingly) exhaustive by
qualified personnel2. American Legal Standard: “reasonable doubt”
See in-class example: Mill’s Method of Residue
The Five Fallacies of Weak Induction
2. Appeal to Unqualified Authority– I was speaking to my brother at his auto shop, and
he believes the Democrats will lose Maryland in the next election. So I think it’s likely.• Premises offer testimony/opinion from an authority• Conclusion about subject matter is made on this basis
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
Question rests on the relevant expertise of the authority consulted
The Five Fallacies of Weak Induction
3. Hasty Generalization
See Presentation “Induction: Generalizations”
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
Two Issues Affecting Strength• Representativeness of Sample• Interviewer Bias
The Five Fallacies of Weak Induction
4. False Cause– Four variants (complex fallacy)
a. Post hoc ergo propter hoc (“after this, there because of this”)
b. Non causa pro causa (“non-cause for the cause”)c. Oversimplified caused. Slippery Slope
The Five Fallacies of Weak Induction
4. False Cause:– After we arrived, the baby got sick. So I think we
were the cause of the baby’s illness.• No causal relation apparent or explained• Causal conclusion based on mere temporal succession
“after this”
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
4. False Cause:– Computer scientists do better at logic. So to do
better in this course, you should study computer science • Typically, no assertion of temporal succession• Mistaken assertion of causal agency
“non-cause”
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
4. False Cause:– Your car is causing global warming. • Phenomenon in question caused by complex number of
factors• A single one of these factors is asserted as sole cause
oversimplification
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
4. False Cause:• If you fail this class, then your GPA will go down. If you GPA falls,
you’ll lose your scholarship. If you lose your scholarship, you’ll spend all your money on school. If you do this, you’ll have no money for food and shelter. So if you fail this class, you will become a starving, homeless beggar. – A chain of causal events is asserted– The causal connection between some or all events is highly
unlikely» At least the ultimate conclusion is highly unlikely
slippery slope
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
5. Weak Analogy
In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
See earlier slides of this presentation!
Two Issues Affecting Strength• Common features relevantly
similar to inferred feature• No relevant dissimilarities
(no disanalogy)
Both my dog and my neighbor's dog are well-loved members of the family. Each one is well fed, house broken, walked on a regular basis. My dog has a very calm temperament. So I infer that my neighbor's dog also has a calm temperament.
Arguments from Analogy?
Fallacies of weak induction– Five identifiable kinds– Not expected to provide the names of these on
exam
Fallacies on Exam
In each case:1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant
conclusion
Homework
• Review:• Fallacies
» pp. 103-105, §4.1 “Fallacies in General”
» pp. 121-131, §4.3 “Fallacies of Weak Induction”
• Inductive Argumentation» Analogical Reasoning, e.g., ex. 8.4» Causal Argumentation, e.g., 8.3b» Inductive Generalization, e.g., 8.2b
• Read for Next Class– pp. 106-116, §4.2 “Fallacies of Relevance”
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