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