Last week Change minds; influence people Premises Conclusion Argument in ordinary life: Change minds; influence people Beliefs you already have Premises (= Assumptions) Beliefs I want you to have Conclusion

Philosophy is like ordinary life: Using arguments to change minds.

Philosophy is like ordinary life: Using arguments to change minds. Philosophy is not like ordinary life: Using arguments for theoretical activity.

Theoretical Activity Asking just to know—without worrying about how answers can be used or applied.

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. It wasn’t as though Edison had the idea of an electric light bulb first, and then went looking for evidence of electrical forces to power his light bulbs.

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. It wasn’t as though Edison had the idea of an electric light bulb first, and then went looking for evidence of electrical forces to power his light bulbs. Without theoretical activity, we wouldn’t have electricity (for example).

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).

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!”

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.

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.

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.

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.

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. X 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.

Rhetorical arguments “pull the wool over the eyes” of the audience. It wasn’t as though Edison had the idea of an electric light bulb first, and then went looking for evidence of electrical forces to power his light bulbs.

Rhetorical arguments “pull the wool over the eyes” of the audience. Useful in practical activities... -advertising -politics -law It wasn’t as though Edison had the idea of an electric light bulb first, and then went looking for evidence of electrical forces to power his light bulbs.

Rhetorical arguments “pull the wool over the eyes” of the audience. 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. I

Three Types of Argument Last week I asked: “What connects the premises with the conclusion?” Probability comes in degrees, of course.

? Beliefs you already have Beliefs I want you to have What does already believing the premises have to do with accepting the conclusion?

? Logic. Beliefs you already have Beliefs I want you to have What does already believing the premises have to do with accepting the conclusion?

? Logic. Well, I lied—sort of... Beliefs you already have Beliefs I want you to have What does already believing the premises have to do with accepting the conclusion? Well, I lied—sort of...

? Logic. There are actually 3 ways for premises Beliefs you already have Logic. Beliefs I want you to have What does already believing the premises have to do with accepting the conclusion? There are actually 3 ways for premises to be “attached” to conclusions.

There are actually 3 ways for premises Logic Deductive argument Beliefs you already have Inductive Argument Generalization Beliefs I want you to have Explanation Abductive Argument What does already believing the premises have to do with accepting the conclusion? There are actually 3 ways for premises to be “attached” to conclusions.

Three Types of Argument Deductive If premises are true, conclusion must be true Inductive If premises are true, conclusion is probably true Probability comes in degrees, of course. Abductive (different) The conclusion explains the premises.

Deductive Arguments

Deductive Arguments The Ideal: Logically valid All premises true

Deductive Arguments The Ideal: Real Life: Logically valid All premises true Real Life: Logically valid All premises agreed upon between arguer and audience

Deductive Arguments Validity Truth

Both of these are valid: Deductive Arguments Validity Truth Both of these are valid: All fish swim All sharks are fish All sharks swim

Both of these are valid: Deductive Arguments Validity Truth Both of these are valid: All fish swim All sharks are fish All sharks swim All fish wear gold chains All sharks are fish All sharks wear gold chains

Both of these are valid: Deductive Arguments Validity Truth Both of these are valid: All fish swim All sharks are fish All sharks swim All fish wear gold chains All sharks are fish All sharks wear gold chains

Validity Truth Deductive Arguments An argument can be invalid even when every statement in it is true. All fish swim All sharks are fish All pimps wear gold chains

Validity Truth Deductive Arguments Valid or Invalid True or False -Inferences True or False -Premises -Assumptions -Claims -Beliefs -Ideas -Sentences

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): God exists because the bible says so 2) Consumer Reports is reliable because it rates itself as reliable.

Deductive Arguments “circular reasoning”? Begging the Question (p. 19): 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

If the premises are true, then the conclusion is probably true. Inductive Arguments If the premises are true, then the conclusion is probably true.

Deductive inferences follow logically Inductive Arguments Deductive inferences follow logically If Tim is taller than Andy and Andy is taller than Bill, it’s impossible for Bill to be taller than Andy.

Inductive Arguments Deductive inferences follow logically If Tim is taller than Andy and Andy is taller than Bill, it’s impossible for Bill to be taller than Andy. Inductive inferences don’t

Inductive Arguments Deductive inferences follow logically If Tim is taller than Andy and Andy is taller than Bill, it’s impossible for Bill to be taller than Andy. Inductive inferences don’t If a woman isn’t wearing a wedding ring, it’s still possible that she’s married.

Induction = Generalization 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.

“2 + 2 = 4” Inductive Arguments Mathematical claims are verified by deduction... “2 + 2 = 4” Scientific claims are verified by induction. “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.

The conclusion explains the premises. Abductive Arguments The conclusion explains the premises. Mendel’s inference: Genes explain patterns of inheritance in pea plants.

The conclusion explains the premises. Abductive Arguments The conclusion explains the premises. Mendel’s inference: Genes explain patterns of inheritance in pea plants. Not an inference about genes in general drawn from observations of particular genes.

Abductive Arguments The conclusion explains the premises. Mendel’s inference: Genes explain patterns of inheritance in pea plants. Not an inference about genes in general drawn from observations of particular genes. Mendel never observed a gene.

Abductive Arguments Likewise, Copernicus didn’t observe the planets orbiting the sun.

Abductive Arguments Likewise, Copernicus didn’t observe the planets orbiting the sun. Newton didn’t observe gravity moving apples toward the ground.

Abductive Arguments Likewise, Copernicus didn’t observe the planets orbiting the sun. Newton didn’t observe gravity moving apples toward the ground. Darwin didn’t observe natural selection.

Why “inference to the best explanation”? Abductive Arguments Why “inference to the best explanation”? Abductive inferences involve hypotheses, and some hypotheses are better than others.

Why “inference to the best explanation”? Abductive Arguments Why “inference to the best explanation”? Abductive inferences involve hypotheses, and some hypotheses are better than others. GOOD IF (hypothetically) the sun orbits the earth, THEN we’d observe what we actually observe.

Why “inference to the best explanation”? Abductive Arguments Why “inference to the best explanation”? Abductive inferences involve hypotheses, and some hypotheses are better than others. GOOD BETTER IF (hypothetically) the sun orbits the earth, THEN we’d observe what we actually observe. IF (hypothetically) the earth orbits the sun, THEN we’d observe what we actually observe.

Abductive Arguments are Weird Like inductive arguments, they come in degrees.

Abductive Arguments are Weird 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 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 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.

The Surprise Principle 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 attack Prediction: the patient has a heart

Abductive Arguments The Surprise Principle You have to consider predictions that distinguish the hypothesis from other explanations. EXAMPLE: Alternative Hyp: the patient isn’t having a heart attack. ...we’d still predict that the patient has a heart.

The Surprise Principle 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.

The Surprise Principle Abductive Arguments The Surprise Principle For a hypothesis to be supported: No false predictions 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)... 30 SLIDES IN 30 MIN

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