WEEK 5 - implicit premises, inductive reasoning, and good arguments

Question 1

what is an argument ?

Answer 1

An argument is a set of statements, one of which (the conclusion) is supposed to be supported by the others (the premises)

Question 2

when is an argument valid ?

Answer 2

An argument is valid if and only if there is no logically possible situation where all the premises are true and the conclusion is false at the same time.

Question 3

when is an argument sound ?

Answer 3

An argument is sound when it is valid and all its premises are true

Question 4

what is an implicit premise ?

Answer 4

Implicit premises are premises that are not explicitly stated

Question 5

“How likely is it that the conclusion is true given that the premises are true?”

Answer 5

• Guaranteed = the argument is valid (if premises are true we know the conclusion is true too)
• Very likely = the argument is inductively strong
• Somewhat likely
• Not at all likely

Question 6

what does inductively strong argument mean ?

Answer 6

An inductively strong argument is an invalid argument whose conclusion is very likely to be true given that its premises are true

Question 7

what does an inductively strong argument’s premises provide?

Answer 7

strong inductive support for its conclusion

Question 8

How to tell whether an argument is inductively strong…

Answer 8

ask: How likely is it that the conclusion is true given that the premises are true?

Question 9

can inductively strong arguments have false premises?

Answer 9

yes, an inductively strong argument needn’t have true premises

Question 10

what does inductively strong mean ?

Answer 10

inductive strength has to do with how much the premises support the conclusion, and not with the actual truth or falsity of the premises and the conclusion

Question 11

what are the two sets of notion for inductive and deductive arguments ?

Answer 11

1. Inductively strong argument Valid argument (have to do with the strength of the connection between an argument’s premises and conclusion)…
2. Inductive/Deductive argument … is a matter of what an argument is “trying” to do

Question 12

what is a deductive argument ?

Answer 12

is an argument that is intended to be valid. One whose conclusion is supposed to be guaranteed by the truth of its premises

Question 13

what is an inductive argument ?

Answer 13

an inductive argument is an argument that is intended to be inductively strong

Question 14

when is an argument valid ?

Answer 14

if and only if there is no logically possible situation where all the premises are true and the conclusion is false at the same start

Question 15

what is an inductively strong argument ?

Answer 15

is an invalid argument whose conclusion is very likely to be true given that its premises are true

Question 16

what are the three points of valid arguments (that are opposite with inductively strong arguments)?

Answer 16

1. it is logically impossible for the premises to be true while the conclusion is false
2. being valid is all or nothing
3. validity is not defeasible

Question 17

what are the three points of inductively strong arguments (that are opposite with valid arguments) ?

Answer 17

1. it is logically possible to be true while the conclusion is false
2. being inductively strong is a matter of degree
3. inductive strength is defeasible

Question 18

difference between an argument and validity :

Answer 18

An argument can be more or less inductively strong, but validity is all or nothing

Question 19

Inductively strength is defeasible but validity is not …

Answer 19

• An inductively strong argument can be made weaker by adding premises
• But a valid argument cannot be made invalid by adding premises

Question 20

can an inductively strong argument also be made stronger by adding premises ?

Answer 20

yes

Question 21

Why is inductive strength defeasible while validity is not?

Answer 21

• in an inductively strong argument, the conclusion is true in most but not all logically possible situations in which the premises are true
• in a valid argument, the conclusion is true in all logically possible situations in which the premises are true

Question 22

what is a “good” argument the same as?

Answer 22

• valid argument
• sound argument
• an inductively strong argument

Question 23

when is an argument sound ?

Answer 23

an argument is sound when it is valid and all its premises are true

Question 24

example of an argument that is valid but not good :

Answer 24

(P1) the moon is made of cheese
(P2) if the moon is made of cheese, then pigs can fly
(C) therefore, pigs fly

Question 25

is this argument valid, invalid, good or bad ?

(P1) the moon is made of cheese
(P2) if the moon is made of cheese, then pigs can fly
(C) studying for exams is lots of fun

Answer 25

valid but not good

Question 26

example of an arguments that is inductively strong but not good…

Answer 26

(P1) 90% of dogs are made of cheese
(P2) spot is a dog
(C) therefore, Spot is made of cheese

Question 27

what are features of a good argument ?

Answer 27

• Have true premises
• Be valid or inductively strong
• Not beg the question
• Have plausible premises
• Have relevant premises

Question 28

why must a good argument have true premises ?

Answer 28

• A good argument should be based on truths, rather than falsehoods
• If an arguments premises are false, we are eld to our conclusion via falsehood

Question 29

why must a good argument be valid or inductively strong ?

Answer 29

• A good arguments conclusion should be highly likely or guaranteed given the truth of its premises
• Note: a good argument doesn’t have to be valid

Question 30

why must a good argument not beg the question ?

Answer 30

An argument begs the question when its premises presuppose its conclusion
E.g. a circular argument begs the question

Question 31

why must a good argument have plausible premises ?

Answer 31

• It is not enough for an arguments premises to happen to be true
• For an argument to be convincing, the premises must be plausible
• There must be good reason to hold them

Question 32

what does plausible mean ?

Answer 32

(of an argument or statement) seeming reasonable or probable