Argument in ordinary life: Change minds; influence people Last week Beliefs you already have Beliefs...
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Transcript of Argument in ordinary life: Change minds; influence people Last week Beliefs you already have Beliefs...
Argument in ordinary life: Change minds; influence people
Last week
Beliefs you already
have
Beliefs I want you to have
Premises
Conclusion
(= Assumptions)
Philosophy is like ordinary life:
Using arguments to change minds.
Philosophy is not like ordinary life:
Using arguments for theoretical activity.
Philosophy is like ordinary life:
Using arguments to change minds.
Asking just to know—without worrying about how answers can be
used or applied.
Theoretical Activity
Theoretical Activity
Asking just to know—without worrying about how answers can be
used or applied.Doesn’t mean theories have no application, just that we aren’t thinking about applications while theorizing.
Theoretical Activity
Without theoretical activity, we wouldn’t have electricity (for example).
Asking just to know—without worrying about how answers can be
used or applied.Doesn’t mean theories have no application, just that we aren’t thinking about applications while theorizing.
When you’re asking just to know, there’s no need for rhetoric.
When you’re asking just to know, there’s no need for rhetoric.
Rhetoric is “tricky” persuasion:trying to convince people of things whether or not they’re really true. (e.g., by appealing to emotion).
“Michael Jackson didn’t do anything wrong. He’s the greatest singer
ever!”
When you’re asking just to know, there’s no need for rhetoric.
Rhetoric is “tricky” persuasion:trying to convince people of things whether or not they’re really true. (e.g., by appealing to emotion).
Conclusion:Michael Jackson didn’t do anything wrong.
Premises:1) Michael Jackson is the greatest singer ever.
Conclusion:Michael Jackson didn’t do anything wrong.
Premises:1) Michael Jackson is the greatest singer ever.Assumption:2) If Michael Jackson is a great singer, then he
wouldn’t do things that are wrong.
Conclusion:Michael Jackson didn’t do anything wrong.
Premises:1) Michael Jackson is the greatest singer ever.Assumption:2) If Michael Jackson is a great singer, then he
wouldn’t do things that are wrong.
?
Conclusion:Michael Jackson didn’t do anything wrong.
Premises:1) Michael Jackson is the greatest singer ever.Assumption:2) If Michael Jackson is a great singer, then he
wouldn’t do things that are wrong.1a) Great singers make people happy. 2a) People who make people happy don’t do
things that are wrong.
Ca) If MJ is a great singer, then he wouldn’t do things that are wrong.
?
Conclusion:Michael Jackson didn’t do anything wrong.
Premises:1) Michael Jackson is the greatest singer ever.Assumption:2) If Michael Jackson is a great singer, then he
wouldn’t do things that are wrong.1a) Great singers make people happy. 2a) People who make people happy don’t do
things that are wrong.
Ca) If MJ is a great singer, then he wouldn’t do things that are wrong.
?
X
Rhetorical arguments “pull the wool over the eyes” of the
audience.
Rhetorical arguments “pull the wool over the eyes” of the
audience.Useful in practical activities...
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Useful in practical activities... -advertising -politics-law
But not theoretical activities. If you’re asking just to know, you don’t want to trick yourself.
Rhetorical arguments “pull the wool over the eyes” of the
audience.
Three Types of Argument
Last week I asked:“What connects the premises with the conclusion?”
Beliefs you already
have
Beliefs I want you to have
?
Beliefs you already
have
Beliefs I want you to have
?
Logic.
Beliefs you already
have
Beliefs I want you to have
?
Logic.
Well, I lied—sort of...
Beliefs you already
have
Beliefs I want you to have
?
Logic.
There are actually 3 ways for premises
to be “attached” to conclusions.
Beliefs you already
have
Beliefs I want you to have
Logic
Generalization
Explanation
Deductiveargument
InductiveArgument
AbductiveArgument
There are actually 3 ways for premises
to be “attached” to conclusions.
DeductiveIf premises are true, conclusion must
be true
Three Types of Argument
InductiveIf premises are true, conclusion is
probably true
Abductive (different)The conclusion explains the premises.
Deductive Arguments
The Ideal:Logically valid
All premises true
Deductive Arguments
The Ideal:Logically valid
All premises true
Deductive Arguments
Real Life:Logically valid
All premises agreed uponbetween arguer and audience
Deductive Arguments
Validity
Truth
Deductive Arguments
Both of these are valid:
All fish swimAll sharks are fishAll sharks swim
Validity
Truth
Deductive Arguments
Both of these are valid:
All fish swimAll sharks are fishAll sharks swim
All fish wear gold chainsAll sharks are fishAll sharks wear gold chains
Validity
Truth
Deductive Arguments
Both of these are valid:
All fish swimAll sharks are fishAll sharks swim
All fish wear gold chainsAll sharks are fishAll sharks wear gold chains
Validity
Truth
Deductive Arguments
Validity
Truth
An argument can be invalid even when every statement in it is true.
All fish swimAll sharks are fishAll pimps wear gold chains
Deductive Arguments
Validity
Truth
True or False-Premises-Assumptions-Claims-Beliefs-Ideas-Sentences
Valid or Invalid-Arguments-Inferences
Deductive Arguments
Quick Quiz:
Last week I said that if an argument makes assumptions, the assumptions are necessary parts of the argument. Why are they necessary?
A) Without them, the premises won’t be valid.B) Without them, the conclusion won’t be true.C) Without them, the argument won’t be true.D) Without them, the argument won’t be valid.
Deductive Arguments
Begging the Question (p. 19):1) God exists because the bible says so
2) Consumer Reports is reliable because it rates itself as reliable.
Deductive Arguments
Begging the Question (p. 19):1) God exists because the bible says so
2) Consumer Reports is reliable because it rates itself as reliable.
Write out premises and conclusion.
What’s the technical meaning of “circular reasoning”?
Inductive Arguments
Inductive Arguments
If the premises are true, then the conclusion is probably true.
Inductive Arguments
Deductive inferences follow logically
If Tim is taller than Andy and Andy is taller thanBill, it’s impossible for Bill to be taller than Andy.
Inductive Arguments
Inductive inferences don’t
Deductive inferences follow logically
If Tim is taller than Andy and Andy is taller thanBill, it’s impossible for Bill to be taller than Andy.
Inductive Arguments
Inductive inferences don’tIf a woman isn’t wearing a wedding ring, it’s stillpossible that she’s married.
Deductive inferences follow logically
If Tim is taller than Andy and Andy is taller thanBill, it’s impossible for Bill to be taller than Andy.
Inductive Arguments
Induction = Generalization
Essential to science: If this salt dissolves in water, then all salt dissolves in water.
Inferences about the world in general
are drawn from a particular sample.
Inductive Arguments
Mathematical claims are verified by deduction...
Scientific claims are
verified by induction.
“2 + 2 = 4”
“Kangaroos don’t lay eggs.”
Inductive Arguments
Deductive inferences are either valid or not—validity doesn’t come in degrees.
Inductive inferences do come in degrees—some generalizations
are stronger than others.
Inductive Arguments
Inductive Strength
1) Sample Size
2) Bias (is sample representative?)
Abductive Arguments
The conclusion explains the premises.
“Inference to the Best Explanation”
Abductive Arguments
The conclusion explains the premises.
“Inference to the Best Explanation”
‘Inference’ is better than ‘argument.’ You can state an inference as an argument, but it’s less useful.
Abductive Arguments
Mendel’s inference: Genes explain patterns of inheritance in pea plants.
The conclusion explains the premises.
Abductive Arguments
Not an inference about genes in general drawn from observations of particular genes.
Mendel’s inference: Genes explain patterns of inheritance in pea plants.
The conclusion explains the premises.
Abductive Arguments
Not an inference about genes in general drawn from observations of particular genes.
Mendel never observed a gene.
Mendel’s inference: Genes explain patterns of inheritance in pea plants.
The conclusion explains the premises.
Abductive Arguments
Copernicus didn’t observe the planets orbiting the sun.
Likewise,
Abductive Arguments
Copernicus didn’t observe the planets orbiting the sun.
Likewise,
Newton didn’t observe gravity moving apples toward the ground.
Abductive Arguments
Copernicus didn’t observe the planets orbiting the sun.
Likewise,
Newton didn’t observe gravity moving apples toward the ground.
Darwin didn’t observe natural selection.
Abductive Arguments
Why “inference to the best explanation”?Abductive inferences involve
hypotheses, and some hypotheses are better than others.
Abductive Arguments
Why “inference to the best explanation”?Abductive inferences involve
hypotheses, and some hypotheses are better than others.
IF (hypothetically) the sun orbits the
earth, THEN we’d observe what we actually observe.
GOOD
Abductive Arguments
Why “inference to the best explanation”?Abductive inferences involve
hypotheses, and some hypotheses are better than others.
IF (hypothetically) the earth orbits the sun, THEN we’d observe
what we actually observe.
IF (hypothetically) the sun orbits the
earth, THEN we’d observe what we actually observe.
GOOD BETTER
Abductive Arguments
Like inductive arguments, they come in degrees.
Abductive Arguments are Weird
Abductive Arguments
Like inductive arguments, they come in degrees.
But unlike inductive arguments, their strength doesn’t depend on the strength (probability) of the premises.
Abductive Arguments are Weird
Abductive Arguments
Like inductive arguments, they come in degrees.
But unlike inductive arguments, their strength doesn’t depend on the strength (probability) of the premises.
Abductive Arguments are Weird
Abductive Arguments
Abductive Arguments are Weird
An abductive argument just says the conclusion is one explanation of the premises.
It doesn’t say how good that explanation is, or whether a better one is available.
Abductive Arguments
The Surprise Principle
To evaluate an abductive inference (a hypothesis), you can’t just look at whether any prediction it makes is true...
EXAMPLE: Hypothesis: the patient is having a heart attackPrediction: the patient has a heart
Abductive Arguments
The Surprise Principle
You have to consider predictions that distinguish the hypothesis from other explanations.
Alternative Hyp: the patient isn’t having a heart attack....we’d still predict that the patient has a
heart.
EXAMPLE:
Abductive Arguments
The Surprise Principle
You have to look at surprising predictions—predictions you wouldn’t make without that hypothesis.
A “prophet” who predicts what everyone already expects to happen has no special powers.
Abductive Arguments
The Surprise Principle
For a hypothesis to be supported:
1) No false predictions2) Some true predictions are
surprising
Abductive Arguments
The “Only Game in Town” Fallacy
What if you only have one hypothesis, so you can’t make
comparisons?
Abductive Arguments
The “Only Game in Town” Fallacy
What if you only have one hypothesis, so you can’t make
comparisons?You can evaluate explanations by themselves, so you don’t have to accept a bad explanation just because it’s “the only game in town.”
Abductive and Inductive Arguments
An Investment Swindle (p. 37)...
Abductive and Inductive Arguments
An Investment Swindle (p. 37)...
Ten predictions in a row were correct.These ten are a representative sample. (Assum.) The investment firm has some way of knowing how well stocks will do.
Hyp 1
Ten predictions in a row were correct.The investment firm got lucky ten times in a row.
Hyp 2