Philosophy 1100: Ethics Topic 1 - Course Introductionheathwoo/phil1100FA16...Logic Logic is the...

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Philosophy 1100: Ethics Topic 1 - Course Introduction: 1. What is Philosophy? 2. What is Ethics? 3. Logic a. Truth b. Arguments c.Validity d. Soundness

Transcript of Philosophy 1100: Ethics Topic 1 - Course Introductionheathwoo/phil1100FA16...Logic Logic is the...

Page 1: Philosophy 1100: Ethics Topic 1 - Course Introductionheathwoo/phil1100FA16...Logic Logic is the study of correct reasoning. In logic, we try to separate the good bits of reasoning

Philosophy 1100: Ethics

Topic 1 - Course Introduction: 1. What is Philosophy? 2. What is Ethics? 3. Logic

a. Truth b. Arguments c. Validity d. Soundness

Page 2: Philosophy 1100: Ethics Topic 1 - Course Introductionheathwoo/phil1100FA16...Logic Logic is the study of correct reasoning. In logic, we try to separate the good bits of reasoning

What is Philosophy?

The Three Fundamental Questions of Philosophy:

• What is there?

• What should I do?

• How can I know?

(Metaphysics)

(Ethics)

(Epistemology)

The three mainbranches of philosophy

(Logic)the fourth main branch

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What is Philosophy?(there are actually many more specific subfields of philosophy as well ... )

philosophy of mind

philosophy of language

philosophy of race

philosophy of action

philosophy of timephilosophy of science

philosophy of law

philosophy of mathematicsphilosophy of religion

feminist philosophy

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What is Ethics?The Three Main Areas of Ethics:

• Metaethics

• Normative Ethics

• Practical Ethics

our classis on

these two (and more onthe first one)

- the attempt to discover(i) the meaning of moral claims(ii) the nature of moral facts (if there are any)(iii) how we can know moral facts.

- the attempt to discoverthe correct moral principles.

- the attempt to discoverthe answers to certain specific moral questions.

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Logic

Logic is the study of correct reasoning.

In logic, we try to separate the good bits of reasoning (also called inferences, or arguments), from the bad bits.

Some concepts from logic that we’ll be introducing: statement, truth, argument, validity, soundness.

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Statements

A statement is a sentence that describes the world as being a certain way.

Statements are either true or false.

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Statements

Some examples of statements:

‘The Earth is round.’‘The Earth is flat.’‘God exists.’‘I hope that God exists.’‘Abortion is wrong.’‘42% of Americans believe that abortion is wrong.’

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Statements

Some examples of sentences that are not statements:

‘What time is it?’‘Close the door, please.’‘Woo Hoo!’‘D’oh!’

(notice that none of these is either true or false)

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Truth

Page 10: Philosophy 1100: Ethics Topic 1 - Course Introductionheathwoo/phil1100FA16...Logic Logic is the study of correct reasoning. In logic, we try to separate the good bits of reasoning

WHAT IS

TRUTH?

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Page 12: Philosophy 1100: Ethics Topic 1 - Course Introductionheathwoo/phil1100FA16...Logic Logic is the study of correct reasoning. In logic, we try to separate the good bits of reasoning

TruthA statement is true when the world actually is the way the statement says the world is.

The definition illustrated:

The statement ‘The Earth is round’ is true just in case the Earth actually is round.

The statement ‘What the teenagers did to the cat was wrong’ is true just in case what the teenagers did to the cat was in fact wrong.

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ArgumentsAn argument is a sequence of statements,the last of which (the conclusion)is supposed to follow from the others (the premises).

Sample argument #1:P1. All men are mortal.P2. Socrates is a man.C. Therefore, Socrates is mortal.

Sample argument #2:P1. A fetus is a person.P2. If a fetus is a person, then

abortion is wrong.C. Therefore, abortion is wrong.

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ValidityA valid argument is one with the following property: if all of its premises are true, then its conclusion must also be true.

In other words:an argument is valid when it is impossible for its premises to be true and its conclusion false.

A valid argument does not require that any of the premises or the conclusion actually be true!

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ValidityValidity Exercises:

Sample argument #1: P1. All men are mortal. P2. Socrates is a man. C. Therefore, Socrates is mortal.

VALID or INVALID ?

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ValidityValidity Exercises:

Sample argument #3:P1. All men are mortal.P2. Boo is not a man. C. Therefore, Boo is not mortal.

VALID or INVALID ?

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ValidityValidity Exercises:

Sample argument #4: P1. All men are mortal. P2. Boo is not a man. C. Therefore, Boo is mortal.

VALID or INVALID ?

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ValidityValidity Exercises:

Sample argument #5: P1. All men are mortal. P2. Boo is a man. C. Therefore, Boo is mortal.

VALID or INVALID ?

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ValidityValidity Exercises:

Sample argument #2: P1. A fetus is a person. P2. If a fetus is a person, then abortion is wrong. C. Therefore, abortion is wrong.

VALID or INVALID ?

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ValidityValidity Exercises:

Sample argument #6:P1. If a fetus is a person, then abortion is wrong.P2. A fetus is not a person.C. Therefore, abortion is not wrong.

VALID or INVALID ?

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ValiditySome common valid argument forms:

Modus PonensP1. PP2. If P, then Q.C. Therefore, Q.

Modus TollensP1. If P, then Q.P2. not-QC. Therefore, not-P.

Multiple Modus PonensP1. PP2. If P, then Q.P3. If Q, then R.C. Therefore, R.

Multiple Modus TollensP1. If P, then Q.P2. If Q, then R.P3. not-RC. Therefore, not-P.

Hypothetical SyllogismP1. If P, then Q.P2. If Q, then R.C. Therefore, if P, then R.

Categorical SyllogismP1. All A’s are B.P2. x is an A.C. Therefore, x is B.

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SoundnessAn argument is sound when(i) it is valid, and(ii) all of its premises are true.

Let’s do a Venn diagram …

So ... all sound arguments are valid, but not all valid arguments are soundit’s much easier for an argument to be valid than it is for it to be soundif we see that an argument is sound, we must accept its conclusion. (not so for validity)

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SoundnessSome sound arguments:

Sample argument #1: P1. All men are mortal. P2. Socrates is a man. C. Therefore, Socrates is mortal.

Sample argument #7:P1. Either Heathwood lives in Denver or Heathwood lives in Boulder.P2. Heathwood does not live in Denver.C. Therefore, Heathwood lives in Boulder.

SOUND

SOUND

SOUND

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Logic

Let’s keep the terminology straight ...

It is statements that can be true or false.

It is arguments that can be valid or invalid, sound or unsound.

There is no such thing as a “true argument”!


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