Who Defined the Study of Philosophy and Logic?

• Socrates, Plato and Aristotle• These three philosophers form the basis of

what is known as Western Philosophy• Every thinker and scientist that followed

used their methods

Socrates b. 470 BCE

• Developed the Socratic method:• A series of questions are used to examine beliefs and develop ideas.

• “The unexamined life is not worth living.”• “ There is only one good, knowledge, and one

evil, ignorance.” • “Know thyself.”• Was executed in Athens after being convicted of

corrupting the youth with his ideas.

Platob. 428 BCE

• Was Socrates’ brilliant student• Traveled extensively before returning to teach at

The Academy.• Allegory of the Cave- the real world is only a

reflection of the truth, of a higher reality • He believed that the perfect political system would

feature “philosopher kings” as it rulers, people versed in ethics and who truly loved only one thing: truth and knowledge

Aristotleb. 384 BCE

• Plato’s student• Aristotle studied almost every single topic from

anatomy to economics to geography, physics, politics, psychology, religion, and even poetry.

• He founded his own school after leaving the Academy, and his center of knowledge became known as the Lyceum.

• Was Alexander the Great’s personal teacher.

Aristotle Part 2

• Developed a vast system of rules for logical thinking to define the world.

• Much like a game has rules, so, too, must logic• Syllogism def. If A=B and B=C, then A=C• Causality: If I set fire to a piece of paper (cause)

then it will burn (effect).• Scientific Method:

• 1. Observe and take notes • 2. Make a theory • 3. Test the theory

What is Logic?• Def. logic is the study of the rules for correct, or valid,

reasoning.

• Deduction: Reasoning that moves from the general to the specific. It is a form of inference where if the premises are true, the conclusion must also be true.– All humans have two legs, the major premise, – I am a human, the minor premise, therefore, – I have two legs, the conclusion.

• Induction: Reasoning that typically moves from specific examples to a larger, general observation. If the premises are true, it is improbable that the conclusion is false.

– '95 households out of 100 have a TV. I am going to stay with Fred, so I will probably be able to watch TV".

Quick check: Stop taking notes!

• I failed that course because the instructor didn’t like me.Assumption: The instructor fails students he doesn’t like.

• I’m not surprised he made the team. After all, his father is the superintendent of schools.Assumption: The superintendent gives special favors to his family

• If I’d only taken my boss to lunch more often, I could have gotten that raise. Assumption: The boss denies raises to people who don’t take him to

lunch very often.

Analyze the assumptions behind every idea!!!

What are the unstated assumptions?

What is a syllogism?

• a specific method of logical deduction(moving from the general to the particular)

every syllogism contains at least three parts:– a major premise (global assumption)– a minor premise (specific claim)– a conclusion

• It’s kind of like simple math

If A = B and B = C, then A = C

A visual representationall things with hairall mammals have hair

mammalsfish do not have hair

fish

Fish are not mammals

Not in your notes -- just think it through!

True vs. Valid Arguments

• True argument = an argument with a conclusion that is considered factually correct.

• Valid argument = an argument with a conclusion that makes sense logically, regardless of whether it is true or not.

True, Valid or Both?

bad driversAll old people are bad drivers.

Old peopleJean is an old person.

Jean

Jean is a bad driver.

If the premises are true, the conclusion would be true.

So this is a valid argument, but obviously false.

True, Valid, or Both

• All fruits have seeds.• Tomatoes have seeds.• Therefore, a tomato is a fruit.

All fruits

Tomatoes

Scientifically, this is valid and true

Is this True, Valid, or Both?

• No human being is immortal.• Ghosts are not human beings.• Therefore, ghosts are immortal.

all things immortal

humanbeings

Faulty logic because this syllogism assumes anything not human is immortal. However, according to some people’s beliefs, this is a true statement: So this is an invalid argument, but a true conclusion.

ghosts

Is this True, Valid, or Both?

• All weeds are plants.• A flower is a plant.• Therefore, all weeds are flowers.

plants

weedsflowers

The conclusion here does not logically follow as a necessary consequence; therefore this argument is invalid.