us nothing about the conclusion.
404 Answers to Selected Exercises
Section B
3. The criteria go from ones closest to our own experience to those furthest.
16. Clearly biased: "masking their greed under a cloak of politics." Suspend judgment on all of it.
22. You're being foolish if you buy the root extract. There's no reason to believe the clerk knows
anything about the subject; most likely he or she is just parroting what they've heard. And the
"Well, it can't hurt" line is just plain false: Lots of quack cures sold at health-food stores can hurt you. You could end up spending thousands of dollars following quack cures before you do
something useful for yourself. On the other hand, you might want to get a second opinion.
25. a. Reject (common knowledge that it's false).
b. Reject—if you know anything about toads and warts. Change doctors.
c. Reject (personal experience. You did notice it rises in the East?).
f. Accept if you haven't been looking at your speedometer, or if you have and you know you
were speeding. Reject if you've been monitoring your speed, saw the speed limit sign, and
you weren't speeding. (But don't sass back.)
g. Suspend judgment (biased source).
j. Accept!! You can't reject this on personal experience, since no personal experience you have
will tell you who got sick worst from which pets in the U.S. during the last year. Cats can
transmit a disease to pregnant women that causes birth defects, and they also cause untold
cases of severe asthma each year. And that's not even counting the infections from clawing.
m. Suspend judgment (contradictory claims).
Section C
7. Donation? See Exercise 1.
8. Why would anyone who can make $250,000 per year playing craps share his secret with you?
Good reason to reject the claim on the first line.
Section D
1. Noting that the conclusion of the argument is true, the person thinks there's good reason to
believe the premises.
6. It may smack of hypocrisy, yet not really be a contradiction. Just because the person who states
the argument apparently doesn't believe the conclusion, that doesn't mean the argument is bad.
9. Suzy really blew it! She's taking the word of an authority over her own experience. Above all
you should trust your own experience.
13. Suzy is right! She says that she has no good reason to believe me, since I'm not an expert on
virtue (I'm a logician, after all). She's not suggesting that I'm wrong, but only that she has no
reason to accept the claim. (Of course, if Suzy knew me better, she'd revise her opinion.)
19. Just a comment on the speaker's apparent inconsistency.
Review Exercises for Chapters 1-5
1. A collection of claims intended to show that one of them, the conclusion, is true.
2. A declarative sentence used in such a way that it is true or false.
3. a. A claim whose truth-value does not depend on what anyone or anything thinks/believes/feels.
4. Yes, depending on the context.
5. a. A claim that says what should be (versus a descriptive claim which says what is).
6. No. A definition is an instruction for how to use a word or words.
7. a. A claim masquerading as a definition.
8. An argument that uses as a (stated or unstated) premise: If you can't make the difference precise, then there is no difference.
Answers to Selected Exercises 405
9. The premises are plausible.
The premises are more plausible than the conclusion.
The argument is valid or strong.
10. a. A valid argument is one in which it is impossible for the premises to be true and the
conclusion false (at the same time).
11. a. A strong argument is one in which it is very unlikely for the premises to be true and the
conclusion false (at the same time).
12. Yes. See the answer to Exercise 9.
13. Give a likely example where the premises are true and the conclusion false.
14. No. From a false premise you can prove anything.
15. Nothing.
16. No. It could beg the question. Or a premise could be false or dubious.
17. No. See the parakeets example in Chapter 3.
18. We assume that the other person who is discussing with us or whose arguments we are reading:
(1) Knows about the subject under discussion, (2) Is able and willing to reason well, and
(3) Is not lying.
19. Someone recognizes that an argument is good but does not believe the conclusion.
20. Given an (implicit) argument that is apparently defective, we are justified in adding a premise or conclusion if: 1. The argument becomes stronger or valid, and 2. The premise is plausible and
would seem plausible to the other person, and 3. The premise is more plausible than the
conclusion. If the argument is valid or strong, yet one of the premises is false or dubious, we may
delete the premise if the argument remains valid or strong.
21. The obvious premise to add to make the argument strong or valid is false.
The obvious premise to add would make the argument weak.
A premise it uses is false or dubious and cannot be deleted.
Two of its premises are contradictory and neither can be deleted.
The argument is so lacking in coherence that there's nothing obvious to add.
There's no argument there.
The conclusion is clearly false.
22. a. A word or phrase added to a claim telling us the role of the claim in an argument or what the
speaker thinks of the claim or argument,
b. No.
23. Our personal experience.
24. Accept as true; reject as false; suspend judgment.
25. We know the claim is true from personal experience.
The claim is made by someone we know and trust and who is an authority on this kind of claim.
The claim is made by a reputable authority whom we can trust as being an expert about this kind
of claim and who has no motive to mislead.
The claim is put forward in a reputable journal or reference source.
The claim is in a media source that's usually reliable and has no obvious motive to mislead, and
the original source is named.
26. We know the claim is false from personal experience.
The claim contradicts other claims we know to be true.
27. When we do not have good reason to believe a claim, and we do not have good reason to think
that the claim is false.
28. He or she believes the premises are true because the argument is valid or strong and the
conclusion is true.
29. He or she says an argument is bad just because of who said it.
406 Answers to Selected Exercises
30. Never.
31. Never.
32. Rejecting an argument because the speaker's actions or words suggest that he/she does
not believe the conclusion of his/her own argument.
Chapter 6
Sections A. 1 and A.2
1. A claim composed of other claims, but which has to be viewed as just one claim.
2. Alternatives.
6. Because each has to be true anyway for the argument to be good.
7. Alternatives: Inflation will go up. Interest rates will go up.
Neither will inflation go up nor will interest rates go up.
11. Alternatives: You're for me. You're against me.
You're neither for me nor against me.
15. Not a claim.
Section A
9. Argument? Yes.
; Conclusion: Lee will vote for the Republican.
Premises: Either you'll vote for the Republican or the Democratic candidate for president. Lee won't vote for the Democrat.
Additional premises needed: None.
Classify: Valid.
Good argument? No. It's a false dilemma. There are other choices for Lee (the candidate for
the Reform Party, the Green Party,. . . ) .
10. Argument? Yes.
Conclusion: Manuel and Tom went to the basketball game.
Premises: Manuel and Tom went to the basketball game if they didn't go to the library.
(= Manuel and Tom went to the basketball game or they went to the library.) They didn't go
to the library.
Additional premises needed: None.
Classify: Valid.
Good argument? Good if the premises are true.
Section B.l
1. a. A claim that can be rewritten as an "if. .. then . .." claim that always has the same truth-value, b. Yes.
5. Here are two samples. Come up with your own.
Don't come home and there'll be hell to pay.
When you get married it means that you can no longer date anyone else.
6. A, but not B.
Answers to Selected Exercises 407
7. a. Suzy studies hard, but she doesn't pass Dr. E's class.
b. Both (b) and (*) could be true (if Dr. E has a kind heart).
c. Both (c) and (*) could be true.
d. Both (d) and (*) could be true in the case that Suzy doesn't study hard, since neither tells us
what happens then.
9. Conditional?, (yes or no) Yes.
Antecedent: Maria goes shopping.
Consequent: Manuel will cook.
Contradictory: Maria goes shopping, but Manuel will not cook.
10. ConditionaP. (yes or no) Yes.
Antecedent: Dick will help Lee with his English exam.
Consequent: Lee will take care of Spot next weekend.
Contradictory: Dick will help Lee with his English exam, but Lee will not take care of Spot
next weekend.
14. ConditionaP. (yes or no) No. An argument. No contradictory.
15. Conditional? (yes or no) Yes.
Antecedent: You'll get me some cake mix.
Consequent: I'll bake a cake.
Contradictory: You get me some cake mix, but I won't bake a cake.
18. Conditional? (yes or no) Yes.
Antecedent: If Dick takes Spot for a walk, Dick will do the dishes.
Consequent: Dick won't take Spot for a walk.
Contradictory: If Dick takes Spot for a walk Dick will do the dishes, and Dick did take Spot for a walk.
Section B.2
1. a. If Flo doesn't have to take a bath, then she didn't play with Spot.
2. a. If Suzy didn't go with Tom to the library, then he didn't get out of practice by 6.
3. a. Neither necessary nor sufficient, c. (i) is sufficient for (ii).
7. a. If Zoe gets a transcript, then she paid her library fines.
Or: If Zoe doesn't pay her library fines, then she won't get her transcript.
8. a. If Maria buys a new dress, then she got a bonus this month. A necessary condition for Maria
to buy a new dress is that she gets a bonus this month.
Section B.3
6. Flo came over early to play, (direct way)
7. Spot didn't bark, (indirect way)
11. None. Appears to be affirming the consequent.
Exercises for Chapter 6
1. Excluding possibilities, the direct way of reasoning with conditionals, the indirect way of
reasoning with conditionals, reasoning in a chain with conditionals, (and in an exercise: no matter
what).
2. Affirming the consequent, denying the antecedent.
3. Affirming the consequent, denying the antecedent, false dilemmas, slippery slope
arguments, (in an exercise: perfectionist dilemma).
6. If you get a credit card, you'll be tempted to spend money you don't have.
If you're tempted to spend money you don't have, you will max out on your card.
If you max out on your card, you'll be in real debt.
408 Answers to Selected Exercises
If you're in real debt, you'll have to drop out of school to pay your bills.
If you drop out of school, you'll end up a failure in life.
So if you get a credit card, you'll end up a failure in life.
But (unstated premise) you don't want to end up a failure in life.
So you shouldn't get a credit card.
7. a. If Dr. E isn't rich, then he didn't win the lottery.
If Dr. E isn't rich, then his book didn't sell a million copies.
If Dr. E isn't rich, then he didn't marry a rich woman,
b. Dr. E won the lottery, but he isn't rich.
Dr. E's book sold a million copies, but he isn't rich.
Dr. E married a rich woman, but he isn't rich.
d. Dr. E winning the lottery is sufficient for Dr. E to be rich.
Dr. E's book selling a million copies is sufficient for Dr. E to be rich.
Dr. E marrying a rich woman is sufficient for Dr. E to be rich.
e. Dr. E being rich is necessary for Dr. E winning the lottery.
Dr. E being rich is necessary for Dr. E's book selling a million copies.
Dr. E being rich is necessary for Dr. E marrying a rich woman.
9. Argument? Yes.
Conclusion: Suzy won't break up with Tom.
Premises: If Suzy breaks up with Tom, then she'll have to return his letter jacket. Suzy won't give up that jacket.
Additional premises needed: None.
Classify : Valid.
Form of argument: Indirect way.
Good argument? Yes.
11. Argument? Yes.
Conclusion: If you take issue with current Israeli policy, you're an anti-Semite.
Premises: If you take issue with current Israeli policy, then you're criticizing Israel. If you criticize Israel, then you're anti-Israel. If you're anti-Israel, you're an anti-Semite.
Additional premises needed: None.
Classify: Valid.
Form of argument: Reasoning in a chain with conditionals.
Good argument? No. Unrepairable: Slippery slope. Last premise in particular is false.
13. Argument? Yes.
Conclusion: It's the ebola virus (in Uganda).
Premises: People in Uganda are dying of some fever where they hemorrhage a lot. If people in
Uganda are dying of hemorrhagic fever, then it's the ebola virus.
Additional premises needed: None.
Classify: Valid.
Form of argument: Direct way.
Good argument? Yes, if premises are true.
14. Argument? Yes.
Conclusion: I should not allow questions in my class.
Bad argument. Slippery slope.
17. Argument? Yes.
Conclusion: Columbus didn't discover America.
Premises: Only if Columbus landed in a place with no people in it could you say he discovered
Answers to Selected Exercises 409
it. The Americas, especially where he landed, were populated. Columbus met natives.
Additional premises needed: If Columbus met natives, then where he landed was populated.
Classify: Valid.
Form of argument: Indirect way (rewrite the "only if' claim as an "if.. . then . . . " claim).
Good argument? Yes.
19. Argument? Yes.
Conclusion: If you lock up someone, he should be locked up forever.
Premises: Every criminal either is already a hardened repeat offender or will become one.
Criminals learn to be hardened criminals in jail. We don't want any hardened criminals
running free on our streets.
Additional premises needed: First argument: If a
criminal is not a hardened repeat offender
and goes to jail, then he will learn to be a hardened repeat offender.* If a criminal goes to jail,
then he will be a hardened repeat offender. Every criminal who is locked up will become a
hardened repeat offender.
Second argument: If we don't want any hardened criminals running free on our streets, then
if we lock up a criminal, we should lock him up forever.
Classify: First argument: Valid—no-matter-what. Second argument: Valid-direct way.
Good argument? No. Premises are dubious, especially *. It's a false dilemma.
20. Argument? Yes.
Conclusion: Mary Ellen went on the Jane Fonda workout plan.
Premises: If Mary Ellen goes on the Jane Fonda workout plan, she'll lose weight. Mary Ellen
lost weight.
Additional premises needed: None.
Classify: Weak.
Form of argument: Affirming the consequent.
Good argument? No.
21. Argument? Yes.
Conclusion: (unstated) Tom will get a dog.
Premises: Dick heard that Tom is going to get a pet. The only pets allowed in this town are
dogs or cats or fish. Tom can't stand cats. Tom doesn't like a pet that you just contemplate.
Tom won't get a fish.
Additional premises needed: If Dick heard that Tom is going to get a pet, then Tom is going to get a pet. (1st conclusion) Tom is going to get a pet. If Tom gets a pet, then it will have to be
a dog or cat or fish. (2nd conclusion) Tom will get a dog or cat or fish. If Tom can't stand
cats, then he won't get a cat. (3rd conclusion) Tom won't get a cat. If Tom doesn't like a pet
that you just contemplate, then Tom won't get a fish. (4th conclusion) Tom won't get a fish.
(5th conclusion) Tom will get a dog.
Classify: Valid.
Form of argument: Direct way (four times) and excluding possibilities.
Good argument? Possibly. Arguments are valid or strong and premises are plausible except for one unstated: "If Dick heard that Tom's going to get a pet, then Tom is going to get a pet."
22. Argument? No. Zoe is just trying to show her Mom is wrong by stating the contradictory. But she gets the contradictory wrong.
Chapter 7
1. No. All I've shown is that the student is (apparently) being irrational.
2. Raising objections to parts of an argument to show the argument is bad.
410 Answers to Selected Exercises
3. Nothing.
4. Answer the objections by showing that they are false or do not destroy the support for your
Richard L Epstein Page 51
