Routledge

Student Material

Chapter 6: Issues in argument-assessment

Students’ material

A

Indicate whether the following claims are true or false.

  1. An argument that is rationally persuasive for you is one by which you are actually persuaded.
  2. If an argument is inductively forceful and you have good reason to accept the premises and the conclusion is not defeated for you, it is rationally persuasive for you.
  3. An invalid argument cannot be rationally persuasive for anyone.
  4. The conclusion of a valid argument cannot be defeated for anyone.
  5. A person can have good reason to accept false premises.
  6. If an argument is rationally persuasive for someone, its premises must be true.
  7. An argument can be rationally persuasive for you even when you don’t judge it to be rationally persuasive for you.
  8. If the conclusion of an argument is false, it cannot be rationally persuasive for anyone.
  9. The same argument can be rationally persuasive for one person, but rationally unpersuasive for another person.
  10. Only deductively and inductively sound arguments can be rationally persuasive.

B

Consider the following cases, and indicate whether the arguments are rationally persuasive for the person in question? NB Questions are in bold.

  1. You and a friend, Ben, are discussing some other friend’s sartorial habits. That friend, Bill, has strange habits such that he always wears the same garments together. You and Ben are discussing whether or not Bill is wearing his red gum boots today. Ben has seen Bill today and reports that Bill is, indeed, wearing his red gum boots. You have no reason to doubt Ben’s testimony. You both know that whenever he wears his red gum boots, he also wears his blue hat. You conjecture as follows:
    P1) Bill is wearing his red gum boots.
    P2) Whenever Bill wears his red gum boots, he also wears his blue hat.
    C) Bill is wearing his blue hat.
    Is the argument rationally persuasive for you?
  2. Now suppose a similar scenario involving a discussion about Bill’s socks. You and Ben both know that whenever Bill wears his blue hat, he usually wears his green scarf. Suppose neither of you have seen Bill today, but you meet up with Beth and Beth tells you that she’s seen Bill today and he’s wearing his blue hat. You have no reason to doubt Beth. On that basis you conjecture as follows:
    P1) Bill is wearing his blue hat today.
    P2) When Bill wears his blue hat, he usually wears his green scarf.
    C) Probably Bill is wearing his green scarf today.
    Is the argument rationally persuasive for you?
  3. Now suppose the same scenario as for question 2, but this time suppose that Beth is colour-blind and cannot distinguish the colour blue. You know that she is colour blind.
    Is the argument in question 2 rationally persuasive for you?
  4. Now suppose the same scenario as for question 3. You know that Beth is colour-blind, but Ben doesn’t know that she’s colour-blind.
    Is the argument in question 2 rationally persuasive for Ben?
  5. Now suppose the same scenario as in question 2 (blue hat, green scarf, Beth’s testimony is reliable), but suppose that later you meet a third friend, Brenda, who tells you that she saw an unusual thing earlier that day – Bill wearing his blue hat but not his green scarf. Brenda tells you that she was quite surprised by this and asked Bill about it, he explained that his scarf was in the wash. You have no reason to doubt Brenda’s testimony.
    Is the argument in question 2 rationally persuasive for you?
  6. Given this new information, is the argument in question 2 rationally persuasive for Ben?
  7. Given what Brenda knows about Bill’s attire today, is the argument in question 2 rationally persuasive for Brenda?
  8. Given this new information, of which Beth is unaware, is the argument in question 2 rationally persuasive for her if she does know the connection between Bill’s blue hat and his green scarf?
  9. Given this new information, is the argument defeated for you?
  10. Given this new information, is the argument defeated for Ben?

C

Consider the following cases, and indicate whether the arguments are rationally persuasive for the person in question? NB Questions are in bold.

  1. Raz, Ruth and Raymond are watching the swimming finals of the 2008 Olympic Games. In the 100 metres freestyle final, Michael Phelps is leading coming out of the final turn when there’s a knock at the door and Raymond gets up to answer it, it is their friend Rosie, who joins them in front of the TV, by this time Raymond and Rosie have missed the end of the race. When they come into the living room, Raz and Ruth tell them that Phelps won and Raymond sees no reason to disbelieve them.  Raymond is pleased because his friend, Ron, who owns a pizza shop, had promised free pizza that night if Phelps won another gold medal. Raymond conjectures as follows:
    P1) Phelps has won another gold medal.
    P2) If Phelps wins another gold medal, there will be free pizza at Ron’s tonight.
    C) There will be free pizza at Ron’s tonight.
    Is the argument rationally persuasive for Raymond?
  2. Is the argument rationally persuasive for Rosie?
  3. Now suppose the same scenario except that, in her excitement, the TV commentator failed to notice that Phelps had been disqualified from the race for a rogue turn. Because they had turned off the TV as soon as they saw Phelps come in first, Raz and Ruth are unaware of his disqualification.
    Is the argument rationally persuasive for Raz and Ruth?
  4. Is the argument defeated for Raymond?
  5. Is the argument defeated for Raz and Ruth?
  6. Now suppose the same scenario as question 1 (so Phelps really has won) but that what Ron had actually said about free pizza was ‘If Phelps wins another gold, I’ll be so happy, I’ll probably give away free pizzas.’ Suppose that Raz, Ruth and Raymond didn’t know this, but Rosie does and she tells them and they have no reason to doubt her. They now conjecture as follows:
    P1) Phelps has won another gold medal.
    P2) If Phelps wins another gold medal, Ron will probably give away free pizzas tonight.
    C) Ron will probably give away free pizzas tonight.
    Is the argument rationally persuasive for Raz, Ruth and Raymond?
  7. Now suppose the same scenario as for question 6, but that Ron is sick and cannot open the pizza shop tonight. Neither Raz, Ruth, Raymond nor Rosie know this.
    Is the argument rationally persuasive for Raz, Ruth, Raymond and Rosie?

  8. Now suppose the same scenario as for question 7, but that Ruth does know that Ron is sick.
    Is the argument defeated for her?
  9. Now suppose the same scenario as for question 8.
    Is the argument rationally persuasive for Ruth?
  10. Now suppose the same scenario as for question 8.
    Is the argument defeated for Raymond?

 

D

The following arguments are inductively forceful. Each one is followed by three statements. For each of the statements, decide whether believing that statement would defeat the argument for you.

 

1. Juan lives in Madrid, the capital of Spain. Most people who live in Madrid are Spanish, and most Spaniards are practising Catholics. So Juan is probably a practising Catholic.

a) Juan is German, not Spanish, and most Germans are not practising Catholics.
b) Juan is not religious.
c) Juan only moved to Madrid last year, before that he lived in Barcelona, where he was born and brought up.

 

2. Fengyi has lost his sunhat. But it'll probably turn up: most things that he loses usually do.

a) The last time Fengyi remembers having his sunhat was yesterday.
b) This is the second time this week that Fengyi has lost his sunhat.
c) Fengyi accidentally dropped his sunhat over the edge of the ferry and into the sea yesterday.

 

3. Farah enjoys watching science fiction television series like Battlestar Galactica, Dr. Who and Star Trek. So she probably liked the film Avatar.

a) Farah prefers reading books to watching television or films.
b) Farah said she didn't enjoy the film Avatar.
c) Farah watched Avatar at the cinema four times.

 

4. The 'Spinning Inverted Death Twist' ride at the fairground is likely to be the kind of ride that old ladies don't like.

a) The 'Spinning Inverted Death Twist' ride was invented in 2009.
b) Despite it's name, the 'Spinning Inverted Death Twist' ride is very gentle, does not involve going upside down, and is not frightening at all.
c) My fifteen year-old brother went on the 'Spinning Inverted Death Twist' ride and he loved it.

5. When the school teacher got to class, there were only three pupils present. So most of the students hadn't come to class.

a) There are four students enrolled in the class.
b) The school teacher is very unpopular with the students.
c) There are 20 students enrolled in the class, and the teacher was fifteen minutes late so 12 students who had come to class had already left before she arrived.

 

6. Jim has bowled for years, while Regina only started last month. So Jim will probably beat Regina at bowling.

a) Jim is terrible at bowling, and Regina is quite good.
b) Regina always loses her temper when she loses any game or competition.
c) Jim often wins bowling competitions.

 

7. It's either a beech, an elm, or an oak. Its leaves don't look like oak leaves, and you rarely get elms around here, so it's probably a beech.

a) It's an elm.
b) It's an oak.
c) It's a beech.

 

8. John will probably be late for the meeting - he's been late for the last four meetings.

a) This is the last meeting.
b) John has promised that this time he won't be late, and John always fulfils his promises.
c) June has been late for the last seven meetings.

 

9. Edouard will probably like the film. It's a comedy and Edouard likes most comedies.

a) The film is badly acted, badly shot, badly plotted, not funny, four hours long, and in Finnish, a language that Edouard does not understand.
b) The film is based on a French novel.
c) The film is set in space, and Edouard doesn't like any films set in space.

 

10. Climbing the stairs from the bottom floor to the top floor takes about two minutes. The journey from the bottom to top floor in the lift only takes one minute. But you usually have to wait for at least a minute and a half for the lift to arrive at the bottom floor. Since we're at the bottom floor, and all we care about is getting to the top floor as quickly as possible, we should climb the stairs.

a) The lift is already at the bottom floor.
b) The lift is broken.
c) The stairs are very steep and slippy.

 

E

The following arguments each rely on a false generalisation which is not stated explicitly. For each argument, give a statement which plausibly expresses the relevant generalisation.

 

1. Although people have tried, nobody has managed to build a cheap, safe, personal jetpack. So no one will ever build a cheap, safe, personal jetpack.

 

2. Although some people say you shouldn’t do it, I enjoy staying in bed until midday at the weekend. So I should stay in bed until midday at the weekend.

 

3. Idrissa's car has broken down even though it has just been to the mechanics. So Idrissa should repair his car himself this time.

 

4. It's clear that civilians shouldn't be allowed to keep guns at their homes. If you have a gun, you can easily kill or seriously injure someone.

 

5. Most people in the UK who are over 21 can drive. This means that most people in the UK who can drive are over 21.

 

6. It won't take you long to tell me what time it is, and it will help me. So you should tell me what time it is.

 

7. Clement the cat can't fly. This is because Clement is not a bird or an insect.

 

8. The majority of the best American Football players are American, but that's just because American Football was invented in the USA.

 

9. I've never had a curry pizza, but I like curry and I like pizza, so I reckon I'd like a curry pizza.

 

10. Downloading 'pirated' mp3s is illegal, but it isn't immoral. Most people who download these mp3s couldn't afford to buy the music legally.

 

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