Strength
Implicit Premises and Conclusions
Definitions
Standard Form
Spot the Error
100
Can an argument be strong without being valid or cogent? Why/why not?
No, in order for an argument to be strong, it must be either valid or cogent. If it is invalid or non-cogent, it cannot be strong. It would be ill-formed.
100
A student says, “The only people who got an A in the course did it by bribing the professor. I conclude that Dan bribed the professor.” Is this argument complete? If not, which premises/conclusions should be added?
No, it is not complete. The implicit premise needed is : Dan is a person who got an A in the course.
100
What is the principle of charitable intent?
Add implicit premises that are reasonable to to accept rather than implicit premises that are obviously false.
100
Dogs make the best pets. They are so loyal, and will love you no matter what.
1. All dogs are loyal. 2. All dogs will love you no matter what. 3. If all dogs are loyal and will love you no matter what, then the make the best pets. 4. Therefore, dogs make the best pets. (from 1,2,3)
100
1. I like icing. Therefore, 2. I like cake.
Missing premise
200
Are all valid or cogent arguments strong? Why/why not, give an example to show your answer.
No, not all valid/cogent arguments are strong. It must be reasonable/justified/rational to believe all the premises are true based on available evidence. An example of a valid argument that is not strong is: All dogs are cats. All cats have fur. Therefore, dogs have fur. An example of a cogent argument that is not strong is: Many professors are aliens. Prof. Kraay is an professor. Therefore, probably, Kraay is an alien.
200
Either I’ll get an A in the course or I’ll get a B. I’ll get an A. What premise/conclusion is missing?
The implicit premise needed is: I won’t get a B.
200
Work is underway to build a bridge. It’s hoped that it will solve traffic problems. What is this an example of?
Descriptive text. Does not provide any reasons, merely describes instead of argues.
200
It’s funny you think vitamin water is healthy. It’s loaded with sugar, and the vitamins in it are ones people already get enough of. Vitamin water is not doing your health any favours.
1. Vitamin water is full of sugar. 2. The vitamins in vitamin water are ones people already get enough of. 3. If vitamin water is full of sugar and the vitamins in it re ones people already get enough of, then it is unhealthy. 4. Therefore, vitamin water is unhealthy. (from 1,2,3)
200
1. If peanut butter is on sale, then you should stock up. 2. Usually, when peanut butter is on sale, then I stock up. 3. Peanut butter is on sale. Therefore, 4. You should stock up.
Unnecessary premise (#2)
300
If the president of the USA is in the White House, then he is in Washington. He is in the White House, so he’s in Washington. Is this argument strong? Why/why not? Does it follow a pattern? If so, which?
Yes, this argument is strong. It is valid, because if the premises were true, it would be impossible for the conclusion to be false, and it is reasonable to believe that all the premises are true based on all available evidence. It follows Modus Ponens, or affirming the antecedent.
300
Make the argument valid: It rained yesterday, so the Red Sox will win the world series this year.
“If it rained yesterday, then the Red Sox will win the world series this year.
300
What is the principle of charity?
Don’t twist other people’s words, for better or for worse, when reconstructing arguments. Formulate reconstruction that is well-formed, has premises that are reasonable/justified/rational for the author/speaker.
300
Professors in the philosophy department are super smart. Philosophy is very hard. Professor Kraay is in the philosophy department, so he definitely is super smart.
1. If philosophy is very hard, then the professors in that department are very smart. 2. Philosophy is very hard. 3. Therefore, professors in the philosophy department are super smart. (from 1,2). 4. Prof. Kraay is in the philosophy department. 5. Therefore, Prof. Kraay is super smart. (From 3,4)
300
1. If Ted goes to the baseball game, he will buy a pretzel. 2. If Ted buys a pretzel, he will put mustard on it. Therefore, 3. If Ted goes to the baseball game, he will put mustard on what he buys. (From 1,2 by hypothetical syllogism)
Inconsistent wording: pretzel --> it --> what he buys
400
All dogs are green. Everything that’s green is a mammal. Therefore, all dogs are mammals. What kind of argument is this? Is is strong? Why/why not? Does it follow an argument pattern? If so, which?
This argument is deductive, because the premises serve to guarantee the conclusion. It is not strong. It is valid, because if both arguments were true, the conclusion would have to be true too. But, it is not strong because it isn’t reasonable to believe that the premises are true based on available evidence. It does follow the pattern of Universal Hypothetical Syllogism.
400
She’s a college professor. So, she must have graduated from college. Reconstruct the argument. What premise/conclusion is missing? What pattern does this argument follow?
Implicit premise: 1. All college professors graduated from college. 2. She is a college professor. 3. Therefore, she must have graduated from college. It follows universal modus ponens.
400
What are the requirements of deductive strength? Inductive strength?
Deductive: 1. Valid, 2. Rational/justified/reasonable for person to believe premises are true based on evidence available Inductive: 1. Cogent, 2. Rational/justified/reasonable for person to believe premises are true based on evidence available, 3. Not defeated by total evidence
400
Either we go to Starbucks or we go to Tim Hortons. I refuse to go to Tim Hortons, because they’re coffee is so bad. So, we’re going to Starbucks.
1. Either we go to starbucks or tim hortons. 2. Tim hortons’ coffee is bad. 3. If tim hortons’ coffee is bad, then I refuse to go there. 4. Therefore, we’re not going to Tim Hortons (from 2,3). 5. So, we’re going to starbucks. (From 1,4).
400
1. All animals with four legs, fur, ears, and paws are dogs. (Implicit premise) 2. Charlie has four legs, fur, ears, and paws. Therefore, 3. Charlie is a dog
Not valid. Missing premise: "Charlie is a dog." Implicit premises uses too broad of a generalization. Should consider narrowing generalization or reconstructing into a cogent argument.
500
Most professors in the philosophy department are really nice and understanding. My critical thinking professor, Kraay, is in the philosophy department. So, probably, he’s nice and understanding. Before hearing a peer state this argument, Nancy went to Kraay’s office hours, where he yelled at her and said her questions were ridiculous. For Nancy, is this argument offered by her peer a strong one? Why/why not, and what requirements of strength does it follow/not follow?
The argument for Nancy is not strong. It is an inductive argument, because the premises serve to make the conclusion probable. It is cogent, because the truth of the premises make the conclusion probable. For the peer, it is rational to believe the premises to be true based on their available evidence. However, for Nancy, it is not strong because the conclusion is defeated. She has evidence independent of the premises that disproves the conclusion.
500
We can safely conclude that Michael is tall. He’s a professional basketball player, and professional basketball players are tall. Reconstruct this argument as a strong one.
1. Most professional basketball players are tall. 2. Michael is a professional basketball player. 3. Therefore, probably, Michael is tall.
500
What are the 3 common mistakes of reconstructing arguments? Describe each.
1. Improper wording: should change works to make argument well-formed 2. Missing premises: leave out premises - misrepresent argument. 3. Unnecessary premises: Non- argumentative material, repetition in reconstruction
500
It’s raining! You said yesterday that if it’s raining, we’ll go see a movie. I think I want to see that new one that is about that dog that breaks his owner out of jail or something. So hurry up let’s go.
1. If it’s raining, we’ll go see a movie. 2. It’s raining. 3. Therefore, we’ll go see a movie (from 1,2).
500
1. When it snows, my little sister will build a snowman. 2. When she builds a snowman, I will put a carrot on the snowman's nose. 3. The snowman will now have a nose. Therefore, 4. When it snows, I will put a carrot on its nose.
- inconsistent wording: sister--> she; snowman--> it - unnecessary premise (#3)
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