Argument Types Flashcards
Deductive arguments
an argument that “is deductively valid or is intended to be deductively valid”.
Non-deductive arguments
any argument that is not deductive
distinction between deductive and non-deductive arguments
both exhaustive and mutually exclusive
two different types of non-deductive
–Inductive arguments
–Abductive arguments
An argument is deductively valid if either
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.
Notes on the deductive validity
- Note that deductive validity, or sometimes just ‘validity’ has nothing to do with whether or not an argument’s premises are in facttrue.
- Validity has to do only with whether the premises would guarantee the truth of the conclusion ifthey were true.
- An assessment of validity is an assessment of the nature of the supportprovided to the conclusion by the premises.
“An argument is invalid if it is not valid.”
- A valid argument cannot have true premises and a false conclusion, while an invalid argument canhave true premises and a false conclusion.
- 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.
“An argument is sound if it is valid and all its premises are true.”
- A deductive argument provides good reason to believe its conclusion only if it is a sound argument.
- Alland onlysound arguments guarantee the truth of their conclusion.
- A deductive argument will be unsound, either if it is invalid or if its premises are untrue.
Non-Deductive Arguments
- However, an argument may be unsound and still be a rationally good argument .
- Very many excellent scientific arguments, including very many excellent arguments in the health sciences, are unsound.
- It is possible for unsound arguments to be good arguments, because some invalid arguments are good arguments.
non-deductively strong
- All good or rational arguments that are deductively invalid are non-deductively strong.
- 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.
- While validity is an all or nothing matter, non-deductive strength is a matter of degree.
cogent non-deductive argument
- Being strong, like being valid, does not make an argument a good or rational argument.
- For a strong argument to give good reason to believe its conclusion it must have true premises.
- A strong argument with true premises is called a cogent argument.
Deductive Arguments vs. Non-Deductive Argument
RELATION OF SUPPORT deductive arguments: valid non-deductive arguments: strong SATISFIESTHE RELATION OF SUPPORT + TRUE PREMISES: deductive arguments: sound non-deductive arguments: cogent
two different types of Non-Deductive Arguments
–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.
Inductive Arguments
- Inductive arguments move from premises that refer to a sample to a conclusion that does not refer to that sample.
- Inductive arguments are generally based on the observation of some sort of frequency in their sample.
- 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).
examples of Inductive Arguments
- “In all trials the drug was effective in treating condition x. So, this drug works well in treating condition x.”
- “80% of cases of disease x are fatal. So, this case of disease x will probably also be fatal.
Abductive Arguments
- Abductive arguments are also referred to as “inference to the best explanation”.
- Unlike inductive arguments, abductive arguments need not appeal to frequencies in a sample.
- Instead, abductive arguments always appeal to explanatory factors.
The logical form of abductive arguments
–Phenomenon Q
–E provides the best explanation for Q
–Therefore, E is probably true
important to distinguish carefully between abductive arguments and explanations
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.
Explanation: “Mary’s husband has lipstick on his collar, because he is cheating.”
•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
Explanation: “You have a runny nose, etc., because you have a cold.”
•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.”
Validity and Strength
- Being either deductively valid or non-deductively strong is necessary but not sufficient for an argument to be a rationally good argument.
- 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.
- Both valid arguments and strong arguments provide good reason to believe their conclusion if their premises are true.
- So, all arguments that are either sound or cogent are rationally convincing and only arguments that are either sound or cogent are rationally convincing.
Conclusion to types of arguments
- Deductive arguments are either valid or intended to be valid.
- A valid argument provides rational grounds to believe its conclusion only if it is sound.
- Inductive and abductive arguments are either strong or intended to be strong.
- Strong arguments provide rational grounds to believe their conclusion only if they are cogent.
- A sound argument guarantees the truth of its conclusion, while a cogent argument significantly raises the probability that its conclusion is true.
- Inductive arguments are based on observed frequencies, while abductive arguments are based on explanatory considerations.