PHIL 1030 Intro to Arguments

Argument

A statement or set of statements (premises) intended to provide evidence for a statement (conclusion)

Valid argument

An argument such that if the premises are true, then the conclusion must be true/cannot be false.

A good argument ...

Establishes its conclusion and gives you a conclusive reason to believe its conclusion

The Rules of Applied Ethics

Can only use moral premises that we all agree to to argue for controversial moral conclusions

Argument Example 1

P1] If X, then Y
P2] X
C] Therefore Y

Is argument example 1 valid or invalid?

Valid

Argument Example 2

P1] If X, then Y
P2] Not X
C] Therefore, not Y

Is argument example 2 valid or invalid?

Invalid

Argument Example 3 & 4

P1] All As are Bs
P2] All Bs are Cs
C] Therefore, all As are Cs

Is argument example 3 & 4 valid or invalid?

Valid

Argument Example 5

P1] If X, then Y
P2] Not Y
C] Therefore, not X

Is argument example 5 valid or invalid?

Valid

Argument Example 6

P1] Either X or Y
P2] Not X (not Y)
C] Therefore, Y (X)

Is argument example 6 valid or invalid?

Valid

Possibilities of Conclusions

1) True possibilities leads to True conclusions
2) True possibilities leads to false conclusions
3) False possibilities leads to true conclusions
4) False possibilities leads to false conclusions

A valid argument rules out which number of the Possibilities of Conclusions?

#2

False premises do not guarantee what?

A false conclusion

A valid argument with a false conclusion guarantees what?

At leas tone premise MUST be false

Truth goes (down or up?)

Down

False goes (down or up?)

Up

For an invalid argument, what is possible?

Any combination of false and true premises and conclusions

Circular arguments

The conclusion is either stated or assumed in the premises. Always valid

What are circular arguments?

Bad arguments

A good argument is

1) Valid
2) Has true premises
3) Not circular

Equivocation

When the same word is used in different premises with different meanings. Always invalid

Suppose you have a valid argument with 3 premises. The conclusion is false, and the first and second premises are true. If so premise 3 ...
a) must be true
b) must be false
c) could be true or false

b) must be false

Suppose you have an invalid argument with all true premises. If so, then the conclusion ...
a) must be true
b) must be false
c) could be true or false

c) could be true or false

Suppose you have a valid argument with two premises. The first premise is true and the second premise is false. If so, then the conclusion ...
a) must be true
b) must be false
c) could be true or false

c) could be true or false

True or False. A valid argument can have a false conclusion.

True

True or False. A valid argument can have false premises.

True

True or False. A valid argument can have true premises and a false conclusion.

False

Valid or Invalid
P1] If Sally has a cake, then Sally can do math in her head
P2] Sally cannot do math in her head
C] Therefore, it is not the case that Sally has a cake

Valid

Valid or Invalid
P1] Sally is not a worrier
P2] People who are risk-averse are worriers
C] Therefore, Sally is not risk-averse

Valid

Valid or Invalid
P1] There are exactly 4 colors
P2] There are many fish in the sea
P3] Love cuts like a knife
P4] You should shop around for the best price
C] Therefore, there are many fish in the sea

Valid

Valid or Invalid
P1] If Frank goes to the ball, then Frank will be eaten by zombies
P2] If Frank will be eaten by zombies, then 2022 is going to be a great year
P3] If 2022 is going to be a great year, then Sally will burn the asparagus
C] Therefore, if Frank goes to the ball, then Sally will burn the asparagus

Valid

Valid or Invalid
P1] Frank is a zombie
P2] Zombies can't tell what regular (non-zombie) people are thinking
C] Therefore, zombies can't tell what Frank is thinking

Invalid

Valid or Invalid
P1] If Frank does not go to the party, then Frank will not meet Sally
P2] Frank does go to the party
C] Therefore, Frank will meet Sally

Invalid

Valid or Invalid
P1] Either Frank passes this quiz, or Frank will fail the course
P2] Frank did not pass this quiz
C] Therefore, Frank will fail the course

Valid

Valid or Invalid
P1] If Sally has another appletini, then Sally will wake up with a Hobo
P2] Sally will wake up with a Hobo
C] Therefore, Sally has another appletini

Invalid

Valid or Invalid
P1] If Frank is dancing, then Frank is drunk
P2] Frank is not dancing
C] Therefore, Frank is not drunk

Invalid

Valid or Invalid
P1] If Frank is dancing, then Frank is drunk
P2] Frank is drunk
C] Therefore, Frank is dancing

Invalid

Valid or Invalid
P1] If Frank is dancing, then Frank is drunk
P2] Frank is not drunk
C] Therefore, Frank is not dancing

Valid

True or False. If an argument is valid, and its premises are false, then its conclusion must be false.

False

True or False. If an argument is invalid, then its conclusion is false.

False

True or False. If an argument has a false conclusion, then the argument must be invalid.

False

Suppose you have an argument that has three premises. The argument is valid, and the argument has a false conclusion. If so then, ...
a) all the premises are true
b) all the premises are false
c) at least one of the premises is false
d) at least one of the premises is true

c) at least one of the premises is false

Suppose you have a valid argument that has three premises. The first premise and the second premise are true, and the conclusion is true. If so, what must be the case with the third premise.
a) it is true
b) it is false
c) it could be true or false

c) it could be true or false

Suppose you have an invalid argument with three premises. Each of the premises are true. If so, the conclusion ...
a) must be true
b) must be false
c) could be true or false

c) could be true or false