phl a11 2014 slides - lecture 2 (jan 14)
TRANSCRIPT
Today: 1. A dis(nc(on: descrip)ve vs. norma)ve 2. Arguments: what they are and how to
evaluate them. Thursday: we begin Unit 1. Read: John Stuart Mill, “In Defense of U)litarianism”
2
Norma)ve versus Descrip)ve
A descrip(ve claim = a claim about what is the case. A norma(ve claim = a claim about how things ought to be.
3
Examples of Descrip)ve Claims
1. Obama is the President of the USA. 2. John Stuart Mill is the President of the USA. 3. 50% of marriages end in divorce. 4. Whales are fish. 5. Leafy green vegetables contain tons of
vitamins, minerals and an)oxidants. 6. Salsa is the #1 condiment in North America.
4
Examples of Norma)ve Claims a. It is wrong to break a promise. b. Ea)ng meat is morally permissible. c. You should eat a lot of leafy greens. d. You should eat a lot of salsa. e. One ought not hold inconsistent beliefs. f. If all the evidence supports that it was
Professor Plum in the library with the candles)ck, you should believe that it was.
5
Norma)ve versus Descrip)ve
• Both descrip)ve and norma)ve claims can be true or false.
• The difference is in subject ma1er: it’s a difference in what the claims are about.
6
Descrip)ve Claims
“John Stuart Mill is the President of the USA.” “Whales are fish.” false
“Salsa is the #1 condiment in North America.” debatable (is it salsa or ketchup??)
7
Morality is a Norma3ve Domain
• Moral claims are claims about how people ought to act, rather than about how people do in fact act.
-‐ “It is wrong to break a promise.” -‐ “Ea)ng meat is morally permissible.”
8
Other Kinds of Norma)ve Claims
Pruden(al claims: claims about what would be prudent, or in your self-‐interest. “You should eat a lot of leafy greens.” “You should eat a lot of salsa.”
9
Other Kinds of Norma)ve Claims Norma(ve epistemic claims: claims about what one should believe, how one ought to reason. “One ought not hold inconsistent beliefs.”
“If all the evidence supports that it was Professor Plum in the library with the candles)ck, you should believe that it was.”
10
Summary
Moral claims are: a) Norma)ve rather than descrip)ve. b) They are a par)cular kind of norma)ve claim.
Not all norma)ve claims concern morality.
11
How can we inves)gate moral ques)ons?
• The chief tool cannot be experiment or observa)on.
• One cannot infer a norma3ve claim from a purely descrip3ve claim.
• “Is” does not imply “Ought”.
12
Psychology, Sociology, Anthropology
• Can tell us about how people in fact behave.
• Can tell us about what people believe about how they ought to behave.
Example: while 90% of Canadians eat meat, only 70% believe that ea)ng meat is morally okay.*
But this cannot tell us whether ea)ng meat is morally okay. *Warning: made up sta)s)c.
13
How can we inves)gate moral ques)ons?
-‐ What we can do is give arguments. -‐ We can start from claims that are highly plausible, and try to argue from those claims to conclusions that are less obvious, or more controversial.
14
An Argument
A series of proposi)ons aimed at establishing or jus)fying some point. Contains: a) a conclusion = the proposi)on the argument
is trying to establish. b) premises = the star3ng points of the
argument.
15
Example
“One should not cause tremendous pain just for one’s own amusement. Puing kijens in boiling water causes them tremendous pain. So, one should not put kijens in boiling water just for one’s own amusement.” What is the conclusion? What are the premises?
16
Answer
P1. One should not cause tremendous pain just for one’s own amusement. P2. Puing kijens in boiling water causes them tremendous pain. C. One should not put kijens in boiling water just for one’s own amusement.
17
Two Ways an Argument Can Go Wrong
1) It could start from false premises. 2) It could have faulty inferences: the moves it
makes from the premises to the conclusion could be bad moves.
18
An Air)ght Argument
1) The premises are true.
2) The inferences are valid: the conclusion follows from the premises.
19
A Valid Argument
• If the premises are true, then the conclusion must be true.
• The conclusion follows from the premises.
20
An Air)ght Argument
1) The premises are true. 2) The inferences are valid. 1) + 2) the conclusion is guaranteed to be true. 1 and 2: completely independent (can have either without the other). 21
What’s Wrong with this Argument?
P1) If the moon is made of tofu, then there is bean curd in the sky. P2) The moon is made of tofu. C) Therefore, there is bean curd in the sky.
22
What’s Wrong with this Argument?
P1) If the moon is made of tofu, then there is bean curd in the sky. P2) The moon is made of tofu. C) Therefore, there is bean curd in the sky. P2 is false.
23
Is the Inference Valid?
P1) If the moon is made of tofu, then there is bean curd in the sky. P2) The moon is made of tofu. C) Therefore, there is bean curd in the sky.
24
Is the Inference Valid?
P1) If the moon is made of tofu, then there is bean curd in the sky. P2) The moon is made of tofu. C) Therefore, there is bean curd in the sky. Ask yourself: If P1 and P2 were both true, could C be false? If the answer is ‘no’, then the inference is valid.
25
Is the Inference Valid?
P1) If the moon is made of tofu, then there is bean curd in the sky. P2) The moon is made of tofu. C) Therefore, there is bean curd in the sky. Yes, the inference is valid.
26
Any Argument of the Form
1. If A then B 2. A 3. Therefore, B is valid. -‐ Called “Modus Ponens”.
27
Is this Argument a Good One?
P1) If I play tennis today, I will get some exercise.
P2) I will not play tennis today. C) Therefore, I’m not going to get any exercise. -‐ The premises are true. -‐ Is the inference valid?
28
Is the Inference Valid?
P1) If I play tennis today, I will get some exercise. P2) I will not play tennis today. C) Therefore, I’m not going to get any exercise. No. Counterexample to its validity: I go jogging.
29
Evalua)ng the Arguments We Read
1. Determine what the conclusion is, what the premises are, and then ask:
2. Are the premises plausible? -‐ How might one object to the them?
1. Are the inferences valid? -‐ If not, what would it take to make the argument valid?
31
Implicit Premises Suppose I say: “All animals are mortal. So, we need to face it: Fido is going to die one day. He’s not going to live forever.” What I said explicitly:
P1. All animals are mortal. C. Therefore, Fido is mortal.
32
Is the Argument a Good One?
P1. All animals are mortal. C. Therefore, Fido is mortal. -‐ P1 is true.
-‐ But the inference is not valid.
Proof: Imagine that “Fido” is the name of a rock. This would make P1 true and C false.
33
Implicit Premise
But it would be a mistake to conclude that my argument was a bad one.
If we were interpre)ng what I was saying charitably, it would be clear that I was making use of an implicit premise:
Fido is an animal.
34
The Argument Really
P1. All animals are mortal. P2. Fido is an animal. C. Therefore, Fido is mortal. -‐ This is a valid argument. -‐ And it has true premises, assuming Fido is indeed an animal.
35
Example
P1. Driving above the speed limit is illegal. C. Therefore it is wrong to drive above the speed limit. -‐The premise is true. -‐But is the inference valid?
36