HW2- Fallacies & Propositions
(solutions)
Due: Friday April 1, 2011
HW #2- SOLUTIONS
Topics: fallacies and propositions
Please show your work and clearly indicate your answer. Although you are welcome to
compare your methods and answers with other students, be careful not to copy off of other
students. When indicated you may use a calculator, otherwise only do so to check your
work.
I. Fallacies
For each of the arguments in 1-5, a) identify the premise(s) and the conclusion [2 points] and
b) explain why there is fallacy in the argument (you do not need to name the specific fallacy)
[4 points]
1. My father tells me I should exercise daily. But he never exercised when he was young, so
I see no need to follow his advice.
a) Premise: My father tells me I should exercise daily
Premise: He never exercised when he was young
Conclusion: I do not need to follow his advice
b) Fallacy: Just because your father did not exercise when he was young does not
make his advice any less valid. This is a Personal Attack fallacy.
2. My baby was vaccinated and later developed autism, which is why I believe that vaccines
cause autism
a) Premise: my baby was vaccinated and later developed autism.
Conclusion: vaccines cause autism.
b) Fallacy: Just because your baby developed autism after getting a vaccine does not
mean that the vaccine caused the autism. This is a fallacy of False Causality.
3. All of those studies about risks of driving without seat belts are flawed. It’s certainly not a
good idea to have your seat belt on if your car is on fire or underwater.
a) Premise: It isn’t a good idea to have your seat belt on if your car is on fire or
underwater.
Conclusion: All of those studies about risks of driving without seat belts are flawed.
b) Fallacy: just because there are two situations in which having your seatbelt on is
harmful, does not mean you should never wear your seatbelt, and it certainly
doesn’t mean that all the studies that say so are false. This is a fallacy of Hasty
Generalization.
4.
Most people don’t wear a helmet while driving their motorcycle, so it must be safe to
drive a motorcycle without wearing a helmet.
a) Premise: Most people don’t wear a helmet while driving their motorcycle.
Conclusion: it is safe to drive a motorcycle without wearing a helmet.
b) Fallacy: just because most people do something doesn’t mean it is safe to do so.
This is a fallacy of Appeal to Popularity.
IGE104: Logic and Mathematics for Daily Living (3-2010)
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HW2- Fallacies & Propositions
(solutions)
Due: Friday April 1, 2011
5. If fat people exercise they can lose weight. So people who are fat should exercise to lose
weight.
a) Premise: If fat people exercise they can lose weight
Conclusion: people who are fat should exercise to lose weight
b) Fallacy: The conclusion is just the premise restated. This is a fallacy of circular
reasoning.
6. Find an article on The Bangkok Post or The Nation that demonstrates a logical fallacy.
Each student should have a different article.
a. Print out a copy of the article and attach it to your HW [2 points]
b. Highlight a fallacy you see [2 points]
c. Explain why what you highlighted is a fallacy [6 points]
II. Propositions
7. Write the negation of the following proposition: [2 points each]
a. Washington, D.C. is the capital of Thailand.
Washington, D.C. is not the capital of Thailand.
b. The weather at this time of year is not supposed to be so cold.
The weather at this time of year is supposed to be this cold.
For the following logical conjunctions or disjunctions (8 -12), a) indicate each individual
proposition and whether each is true or false [4 points], then b) state whether the entire
statement is true or false and explain why [2 points].
8. Cats have four legs and whales have no legs
a) p: Cats have four legs (T)
q: whales have no legs (T)
b) The entire statement is true since both propositions are true.
9. 12 + 6 = 18 and 6 x 4 = 18
a) p: 12 + 6 = 18 (T)
q: 6 x 4 = 18 (F)
b) The entire statement is false since at one of the propositions is false.
10. Some people are short and some people are tall.
a) p: some people are short (T)
q: some people are tall (T)
b) The entire statement is true since both propositions are true.
11. 2 x 5 = 10 or 23 + 8 = 31
a) p: 2 x 5 = 10 (T)
q: 23 + 8 = 31 (T)
b) The entire statement is true since both propositions are true.
12. Either Beethoven or Gandhi was a professional baseball player.
a) p: Beethoven was a professional baseball player (F)
q: Gandy was a professional baseball player (F)
b) The entire statement is false since both propositions are false.
IGE104: Logic and Mathematics for Daily Living (3-2010)
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HW2- Fallacies & Propositions
(solutions)
Due: Friday April 1, 2011
For the following if…then… statements (13 – 15) a) identify the hypothesis and the
conclusion [2 points], b) state their truth values [2 points], and c) determine whether the
entire statement is true or false and explain why [2 points].
13. If Italy is in Europe, then China is in Asia.
a) Hypothesis: Italy is in Europe
conclusion: China is in Asia
b) The hypothesis is True and the conclusion is True
c) The entire statement is True since the hypothesis is True and the conclusion is True.
14. If Einstein was a scientist, then Eminem is a singer.
a) Hypothesis: Einstein was a scientist
conclusion: Eminem is a singer
b) The hypothesis is True and the conclusion is True
c) The entire statement is True since the hypothesis is True and the conclusion is True.
15. If bees can fly, then bees are birds.
a) Hypothesis: bees can fly
conclusion: bees are birds
b) The hypothesis is True and the conclusion is False
c) The entire statement is False since the hypothesis is True and the conclusion is False.
IGE104: Logic and Mathematics for Daily Living (3-2010)
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