Argument Types

Question 1

Deductive arguments

Answer 1

an argument that “is deductively valid or is intended to be deductively valid”.

Question 2

Non-deductive arguments

Answer 2

any argument that is not deductive

Question 3

distinction between deductive and non-deductive arguments

Answer 3

both exhaustive and mutually exclusive

Question 4

two different types of non-deductive

Answer 4

–Inductive arguments

–Abductive arguments

Question 5

An argument is deductively valid if either

Answer 5

1.If its premises were all true then its conclusion would have to be true.
Or (equivalently):
2.It is not logically possible for all its premises to be true and its conclusion false.

Question 6

Notes on the deductive validity

Answer 6

1. Note that deductive validity, or sometimes just ‘validity’ has nothing to do with whether or not an argument’s premises are in facttrue.
2. Validity has to do only with whether the premises would guarantee the truth of the conclusion ifthey were true.
3. An assessment of validity is an assessment of the nature of the supportprovided to the conclusion by the premises.

Question 7

“An argument is invalid if it is not valid.”

Answer 7

1. A valid argument cannot have true premises and a false conclusion, while an invalid argument canhave true premises and a false conclusion.
2. Giving a logically possible counterexample in which an argument’s premise(s) are true and the conclusion false is sufficient to show that the argument is invalid.

Question 8

“An argument is sound if it is valid and all its premises are true.”

Answer 8

1. A deductive argument provides good reason to believe its conclusion only if it is a sound argument.
2. Alland onlysound arguments guarantee the truth of their conclusion.
3. A deductive argument will be unsound, either if it is invalid or if its premises are untrue.

Question 9

Non-Deductive Arguments

Answer 9

1. However, an argument may be unsound and still be a rationally good argument .
2. Very many excellent scientific arguments, including very many excellent arguments in the health sciences, are unsound.
3. It is possible for unsound arguments to be good arguments, because some invalid arguments are good arguments.

Question 10

non-deductively strong

Answer 10

1. All good or rational arguments that are deductively invalid are non-deductively strong.
2. If the premises of a strong argument are true, then they significantly increase the likelihood that the conclusion is true without guaranteeing that the conclusion is true.
3. While validity is an all or nothing matter, non-deductive strength is a matter of degree.

Question 11

cogent non-deductive argument

Answer 11

1. Being strong, like being valid, does not make an argument a good or rational argument.
2. For a strong argument to give good reason to believe its conclusion it must have true premises.
3. A strong argument with true premises is called a cogent argument.

Question 12

Deductive Arguments vs. Non-Deductive Argument

Answer 12

RELATION OF SUPPORT
deductive arguments: valid 
non-deductive arguments: strong 
SATISFIESTHE RELATION OF SUPPORT + TRUE PREMISES:
deductive arguments: sound 
non-deductive arguments: cogent

Question 13

two different types of Non-Deductive Arguments

Answer 13

–Inductive Arguments
–Abductive Arguments (sometimes called “Inference to the best explanation”)
•Both abductive and inductive arguments are either strong arguments or are intended to be strong.

Question 14

Inductive Arguments

Answer 14

1. Inductive arguments move from premises that refer to a sample to a conclusion that does not refer to that sample.
2. Inductive arguments are generally based on the observation of some sort of frequency in their sample.
3. The conclusion can be about the future (based on the past), the characteristics of a population (based on a sample), the characteristics of an individual (based on a sample of other individuals) or a causal connection (based on samples of correlation).

Question 15

examples of Inductive Arguments

Answer 15

1. “In all trials the drug was effective in treating condition x. So, this drug works well in treating condition x.”
2. “80% of cases of disease x are fatal. So, this case of disease x will probably also be fatal.

Question 16

Abductive Arguments

Answer 16

1. Abductive arguments are also referred to as “inference to the best explanation”.
2. Unlike inductive arguments, abductive arguments need not appeal to frequencies in a sample.
3. Instead, abductive arguments always appeal to explanatory factors.

Question 17

The logical form of abductive arguments

Answer 17

–Phenomenon Q
–E provides the best explanation for Q
–Therefore, E is probably true

Question 18

important to distinguish carefully between abductive arguments and explanations

Answer 18

Abductive arguments are arguments because they are intended to show that something (the argument’s conclusion) is the case rather than why something (an explanandum) is the case.

Question 19

Explanation: “Mary’s husband has lipstick on his collar, because he is cheating.”

Answer 19

•Abductive Argument: “Mary’s husband has lipstick on his collar. The best explanation for this is that he is cheating. Therefore, Mary’s husband is probably cheating

Question 20

Explanation: “You have a runny nose, etc., because you have a cold.”

Answer 20

•Abductive Argument: “A patient has a runny nose, sore throat, sneezing. The best explanation of these symptoms is that she has a cold. She probably has a cold.”

Question 21

Validity and Strength

Answer 21

1. Being either deductively valid or non-deductively strong is necessary but not sufficient for an argument to be a rationally good argument.
2. Only arguments that are either valid or strong provide good reason to believe their conclusion but not all arguments that are either valid or strong provide good reason to believe their conclusion.
3. Both valid arguments and strong arguments provide good reason to believe their conclusion if their premises are true.
4. So, all arguments that are either sound or cogent are rationally convincing and only arguments that are either sound or cogent are rationally convincing.

Question 22

Conclusion to types of arguments

Answer 22

1. Deductive arguments are either valid or intended to be valid.
2. A valid argument provides rational grounds to believe its conclusion only if it is sound.
3. Inductive and abductive arguments are either strong or intended to be strong.
4. Strong arguments provide rational grounds to believe their conclusion only if they are cogent.
5. A sound argument guarantees the truth of its conclusion, while a cogent argument significantly raises the probability that its conclusion is true.
6. Inductive arguments are based on observed frequencies, while abductive arguments are based on explanatory considerations.