Fallacy
• Fallacies are defects in an argument.
• Fallacies cause an argument to be invalid, unsound, or weak.
Formal Fallacies
• Identified through discrepancies in syllogistic patterns and terms.
• Only found in deductive arguments.
• For a deductive argument to be valid, it must be absolutely impossible for both its premises to be true and its conclusion to be false. With a good deductive argument, that simply cannot happen; the truth of the premises entails the truth of the conclusion.
The classic example of a deductively valid argument is:
– 1. All men are mortal. (premise)
– 2. Socrates is a man. (premise)
– 3. Therefore Socrates is mortal. (guaranteed conclusion)
– It is simply not possible that both (1) and (2) are true and
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Informal Fallacies
Fallacy: Burden of Proof
Appeal to Ignorance ("Ad Ignorantiam")
Description of Burden of Proof
Burden of Proof is a fallacy in which the burden of proof is placed on the wrong side. Another version occurs when a lack of evidence for side A is taken to be evidence for side B in cases in which the burden of proof actually rests on side B. A common name for this is an Appeal to Ignorance. This sort of reasoning typically has the following form:
1. Claim X is presented by side A and the burden of proof actually rests on side B.
2. Side B claims that X is false because there is no proof for X.
A very common example of this would be: “God exists because there is no proof that He does not.”
Fallacy: Appeal to Authority
Also Known as: Ad Verecundiam
Description of Appeal to Authority
An Appeal to Authority is a fallacy with the following form:
1. Person A is (claimed to be) an authority on subject
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P is presented, with the intent to create pity.
2. Therefore claim C is true.
This line of "reasoning" is fallacious because pity does not serve as evidence for a claim. This is extremely clear in the following case: "You must accept that 1+1=46, after all I'm dying..." While you may pity me because I am dying, it would hardly make my claim true.
Fallacy: Hasty Generalization
Also Known as: Fallacy of Insufficient Statistics, Fallacy of Insufficient Sample, Leaping to A Conclusion, Hasty Induction.
Description of Hasty Generalization
This fallacy is committed when a person draws a conclusion about a population based on a sample that is not large enough. It has the following form:
1. Sample S, which is too small, is taken from population P.
2. Conclusion C is drawn about Population P based on S.
The person committing the fallacy is misusing the following type of reasoning, which is known variously as Inductive Generalization, Generalization, and Statistical Generalization:
1. X% of all observed A's are B''s.
2. Therefore X% of all A's are Bs.
The fallacy is committed when not enough A's are observed to warrant the conclusion. If enough A's are observed then the reasoning is not