WEEK 5 - implicit premises, inductive reasoning, and good arguments Flashcards
what is an argument ?
An argument is a set of statements, one of which (the conclusion) is supposed to be supported by the others (the premises)
when is an argument valid ?
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.
when is an argument sound ?
An argument is sound when it is valid and all its premises are true
what is an implicit premise ?
Implicit premises are premises that are not explicitly stated
“How likely is it that the conclusion is true given that the premises are true?”
- 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
what does inductively strong argument mean ?
An inductively strong argument is an invalid argument whose conclusion is very likely to be true given that its premises are true
what does an inductively strong argument’s premises provide?
strong inductive support for its conclusion
How to tell whether an argument is inductively strong…
ask: How likely is it that the conclusion is true given that the premises are true?
can inductively strong arguments have false premises?
yes, an inductively strong argument needn’t have true premises
what does inductively strong mean ?
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
what are the two sets of notion for inductive and deductive arguments ?
- Inductively strong argument Valid argument (have to do with the strength of the connection between an argument’s premises and conclusion)…
- Inductive/Deductive argument … is a matter of what an argument is “trying” to do
what is a deductive argument ?
is an argument that is intended to be valid. One whose conclusion is supposed to be guaranteed by the truth of its premises
what is an inductive argument ?
an inductive argument is an argument that is intended to be inductively strong
when is an argument 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 start
what is an inductively strong argument ?
is an invalid argument whose conclusion is very likely to be true given that its premises are true
what are the three points of valid arguments (that are opposite with inductively strong arguments)?
- it is logically impossible for the premises to be true while the conclusion is false
- being valid is all or nothing
- validity is not defeasible
what are the three points of inductively strong arguments (that are opposite with valid arguments) ?
- it is logically possible to be true while the conclusion is false
- being inductively strong is a matter of degree
- inductive strength is defeasible
difference between an argument and validity :
An argument can be more or less inductively strong, but validity is all or nothing
Inductively strength is defeasible but validity is not …
- An inductively strong argument can be made weaker by adding premises
- But a valid argument cannot be made invalid by adding premises
can an inductively strong argument also be made stronger by adding premises ?
yes
Why is inductive strength defeasible while validity is not?
- 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
what is a “good” argument the same as?
- valid argument
- sound argument
- an inductively strong argument
when is an argument sound ?
an argument is sound when it is valid and all its premises are true
example of an argument that is valid but not good :
(P1) the moon is made of cheese
(P2) if the moon is made of cheese, then pigs can fly
(C) therefore, pigs fly
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
valid but not good
example of an arguments that is inductively strong but not good…
(P1) 90% of dogs are made of cheese
(P2) spot is a dog
(C) therefore, Spot is made of cheese
what are features of a good argument ?
- Have true premises
- Be valid or inductively strong
- Not beg the question
- Have plausible premises
- Have relevant premises
why must a good argument have true premises ?
- 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
why must a good argument be valid or inductively strong ?
- 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
why must a good argument not beg the question ?
An argument begs the question when its premises presuppose its conclusion
E.g. a circular argument begs the question
why must a good argument have plausible premises ?
- 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
what does plausible mean ?
(of an argument or statement) seeming reasonable or probable
