Logic test

Logic

-the science of sound reasoning

-born in Greece

-formulated the logic theory

-300BC (ish)

Who was the father of (formal) logic?

Aristotle

3 Laws of Logic (Aristotle)

1. Law of Identity

2. Law of Non-Contradiction

3. Law of the Excluded Middle

Law of IDENTITY

-A=A; an object is what it is for all time

-ex. A chair is a chair and will remain a chair for all time. It will never be a table while it is a chair.

Law of NON-CONTRADICTION

-a statement cannot be both true and false

-ex. A shirt is either blue or green. It is not both blue and green.

Law of the EXCLUDED MIDDLE

-any statement is either fully true or fully false

-ex. A woman is either pregnant or she isn't. She can't be partially pregnant.

The Charioteer Analogy

-a wild horse = appetite/desires

-a controlled thoroughbred = spirit

-a charioteer who guides these 2 horses = reason

LOGICAL OR NO?

Mr Cibik is a harsh grader. Nobody got above a 'B' on his last exam according to some freshmen.

ILLOGICAL

-it doesn't have a strong base or evidence from the original source supporting it

-maybe some of the kids that got 'Bs' didn't study

LOGICAL OR NO?

It looks like Kevin is in trouble in school again. He was in the principal's office last week, and a couple days later his parents had to see the principal. He told me he was caught smoking in the locker room right after the fight he had with Joseph in the lunch room. I haven't seen him at school the last couple days. He was probably suspended.

LOGICAL

-lots of evidence from the original source and a strong base

-sound reasoning

LOGICAL OR NO?

Jess is lonely. We tried inviting her to hang out with us twice, but she's never showed up. I bet she has no friends.

ILLOGICAL

-she might have other friends that you don't know about

-she might be shy

LOGICAL

-she might not have any friends

-she might be shy

Two types of reasoning

1. inductive

2. deductive

Inductive reasoning

-reasoning in which you draw a conclusion based on evidence you collect

-"probably", "reasonably", "fairly certain"

Ex. Every time I eat peanuts, I cough. I'm probably allergic to peanuts.

Deductive reasoning

-reasoning in which your conclusion is based on truths

-"therefore", "it must follow", "undeniably"

Ex. Syllogism

Syllogism

-a form of deductive reasoning consisting of a major premise, a minor premise, and a conclusion

-A is B, C is A, C is B

Ex. All men are mortal. Socrates is a man. Socrates is mortal.

Devices that go against sound logic

Appeals and fallacies

5 appeals

-appeal to traditions

-appeal to authority

-appeal to pity/emotion

-appeal to bandwagon

-appeal to the masses

7 fallacies

-personal attack

-denying the source

-blocking disagreement

-lip service

-rationalizing

-slippery slope

-hasty generalization

Appeal to traditions

Uses traditions to get people to act a certain way

Appeal to authority

Uses an expert or celebrity to sway people

Appeal to pity/emotion

Uses guilt-tripping/emotional actions to convince people

Appeal to bandwagon

Uses the fact that a sizable number of people believe or in something as evidence that it must therefore be true

Appeal to the masses

Uses things that people feel strongly about to make it seem like the speaker is on their side

Personal attack

Directly tears someone down

Denying the source

Discredits the validity of the source

Blocking disagreement

Convinces the listener that they would have to be stupid or naive to disagree with them

Lip service

Says what the listeners want to hear, but still disagrees

Rationalizing

Where the real issue is being ignored

Slippery slope

Convinces the listener that a small first step will lead to a chain of events

Hasty generalization

A claim is made, but is based on a sample too small to justify the claim

FINISH THE SYLLOGISM

If someone wants to go to college, they must study hard. Roberto wants to go to college. ____

Roberto must study hard.

FINISH THE SYLLOGISM

If x=4, then 2x=8. x=4.

2x=8

SOUND OR NO?

All flowers have pedals.

Cherry blossoms are flowers.

Cherry blossoms have pedals.

Not sound—not all flowers have pedals. It is valid, though.

SOUND OR NO?

All people are created by God.

Josie is a person.

Josie is created by God.

Yes, it is sound—the first two lines are true, which means that as long as the terms are in the right spots, which they are, the bottom line is correct. Also valid.

SOUND OR NO?

All vegetables are healthy.

Strawberries are fruit.

Strawberries are healthy.

Yes, it is sound—the first two lines are true, but this syllogism is not valid. The terms are incorrect.

Why is reason so highly regarded?

Reason is regarded highly due to how it controls the appetite (desires) and balances the appetite with spirit (the Charioteer Analogy)

How do appeals and fallacies interfere with logic?

-they distract the person from the real issue

-they don't have good evidence or bases