PHIL 105 Lesson 7 UPDATED ACTUAL
Exam Questions and CORRECT Answers
Deductive arguments are always valid. - CORRECT ANSWER - False. Deductive
arguments aim at validity, or are supposed to be valid, or are intended to be valid, but that does
not ensure that deductive arguments always succeed in being valid. Some arguers try to make
their arguments valid, but they fail, and then their arguments are deductive but invalid.
Deductive validity comes in degrees. - CORRECT ANSWER - False. Deductive validity
depends on what is possible or impossible. If it is possible for the premises of an argument to be
true when the conclusion is false, then the argument is invalid. If that combination of truth values
is impossible, then the argument is valid. This combination cannot be partly possible or a little
possible, so an argument cannot be partly valid or a little valid.
Inductive strength comes in degrees. - CORRECT ANSWER - True.
An inductive argument is stronger when its premises provide more and better reason for its
conclusion. The premises can provide a very strong reason or a moderately strong reason or only
a weak reason. The argument is strong to the degree that it provides strong reason for its
conclusion. More technically, inductive strength is a matter of probability—specifically, how
probable the conclusion is, given the premises. Probability does come in degrees. It varies from 0
to 1. This will be explained in two weeks. The point for now is just that, unlike possibility,
probability does come in degrees, so inductive strength also comes in degrees.
Deductive validity is defeasible. - CORRECT ANSWER - False. An argument is valid if it
is not possible for the premises of that argument to be true when its conclusion is false. If that
combination of truth values really is impossible, then adding more premises cannot make that
combination possible. Thus, adding more premises cannot turn a valid argument into an invalid
argument. That is what it means to call validity indefeasible. (Notice, in contrast, that invalidity
is defeasible. If you add more premises to an invalid argument, then you can turn an invalid
argument into a valid argument. One simple way to do this is to add the conclusion as a premise.
Then the argument is circular, but it is valid nonetheless.)
Inductive strength is defeasible. - CORRECT ANSWER - True. To say that inductive
strength is defeasible is to say that adding new premises can turn a strong inductive argument
into a weak inductive argument. That is possible when the argument is not valid. The classic
example is that many people observed thousands of swans throughout six continents and
,concluded that all swans are white. That was a decently strong inductive argument, because their
sample was very large and diverse. But then they learned about black swans in Australia. As soon
as they had that new information in their premises, they ceased to have any reason at all to
believe that all swans are white.
Inductive arguments always have general conclusions. - CORRECT ANSWER - False.
Here's an inductive argument with a particular conclusion: "Most birds can fly, and this owl is a
bird, so probably this owl can fly." Here's another: "The best explanation of the evidence at the
crime scene is that Richard killed the victim, so Richard probably did kill the victim." Each of
these arguments is invalid and defeasible, so they are inductive, even though they do not have
general conclusions.
Deductive arguments always provide more reason for their conclusions than inductive arguments
do. - CORRECT ANSWER - False. Some inductive arguments (such as "The sun has risen
every day for thousands of years, so it will probably rise tomorrow") provide very strong reasons
for their conclusions. Some deductive arguments (such as "There is life on Mars, so there is life
on either Mars or Saturn") provide very little reason for their conclusions, because there is very
little reason for their premises. The former arguments provide more reason for their conclusions
than the latter. Hence, some inductive arguments provide more reason for their conclusions than
some deductive arguments do.
Indicate whether the argument is deductive or inductive. Assume a standard context as described.
Nothing tricky!
Context: You and I want to go for a walk, but it is raining, and we do not want to walk in the
rain. You ask me when I think it will stop raining. Then I say this sentence:
"The sun is coming out, so the rain will probably stop soon." - CORRECT ANSWER -
Inductive.
The word "probably" suggests that this argument is not intended as a valid proof of its
conclusion. When an argument is valid, it is necessary—not just probable—that the conclusion is
true if the premises are true. Thus, if an arguer says only that the conclusion is probably true
given the premises, then that person does not intend the argument to be valid. This makes the
argument inductive.
Indicate whether the following argument is deductive or inductive. Assume a standard context as
described. Nothing tricky!
, Context: Harold is accused of a burglary, but we know him and thought he was a nice person, so
we do not know whether to believe that he is guilty. Then you give this argument.
"If Harold were innocent, then he would not go into hiding. Since he is hiding, he must not be
innocent." - CORRECT ANSWER - Deductive. This argument is valid because its
conclusion can never be false while both of its premises are true. To see this, just try to tell a
coherent story where the premises are all true and the conclusion is false. You can't, so the
argument is valid. Almost all arguments that are valid were intended to be valid. Hence, this
argument was probably intended to be valid. That makes it deductive.
Indicate whether the following argument is deductive or inductive. Assume a standard context as
described. Nothing tricky!
Context: Harold is accused of a burglary. We think that he is not guilty, but we worry that he
might be punished anyway. Then I give this argument.
"If Harold is not innocent, then he will be punished. But he is innocent, so he will not be
punished." - CORRECT ANSWER - Deductive. This argument is not valid, because its
conclusion can be false even if both of its premises are true. Some people are punished by
mistake when they are innocent. Nonetheless, this argument looks like another argument that is
valid (such as this different argument: "If Harold is innocent, then he will not be punished. But
he is innocent, so he will not be punished."). This similarity to a valid argument might make the
argument in our example appear valid. That appearance suggests that the person who gave the
argument in our example intended the argument to be valid. That intention makes the argument
deductive even if it fails to be valid.
Indicate whether the following argument is deductive or inductive. Assume a standard context as
described. Nothing tricky!
Context: I order a cola drink at midnight. You comment that you never drink cola that late at
night, because the caffeine in cola keeps you from sleeping well. I respond with this argument:
"Cola drinks never keep me awake at night. I know because I drank a cola drink just last night
without any problems." - CORRECT ANSWER - Inductive. This argument is not valid and
Exam Questions and CORRECT Answers
Deductive arguments are always valid. - CORRECT ANSWER - False. Deductive
arguments aim at validity, or are supposed to be valid, or are intended to be valid, but that does
not ensure that deductive arguments always succeed in being valid. Some arguers try to make
their arguments valid, but they fail, and then their arguments are deductive but invalid.
Deductive validity comes in degrees. - CORRECT ANSWER - False. Deductive validity
depends on what is possible or impossible. If it is possible for the premises of an argument to be
true when the conclusion is false, then the argument is invalid. If that combination of truth values
is impossible, then the argument is valid. This combination cannot be partly possible or a little
possible, so an argument cannot be partly valid or a little valid.
Inductive strength comes in degrees. - CORRECT ANSWER - True.
An inductive argument is stronger when its premises provide more and better reason for its
conclusion. The premises can provide a very strong reason or a moderately strong reason or only
a weak reason. The argument is strong to the degree that it provides strong reason for its
conclusion. More technically, inductive strength is a matter of probability—specifically, how
probable the conclusion is, given the premises. Probability does come in degrees. It varies from 0
to 1. This will be explained in two weeks. The point for now is just that, unlike possibility,
probability does come in degrees, so inductive strength also comes in degrees.
Deductive validity is defeasible. - CORRECT ANSWER - False. An argument is valid if it
is not possible for the premises of that argument to be true when its conclusion is false. If that
combination of truth values really is impossible, then adding more premises cannot make that
combination possible. Thus, adding more premises cannot turn a valid argument into an invalid
argument. That is what it means to call validity indefeasible. (Notice, in contrast, that invalidity
is defeasible. If you add more premises to an invalid argument, then you can turn an invalid
argument into a valid argument. One simple way to do this is to add the conclusion as a premise.
Then the argument is circular, but it is valid nonetheless.)
Inductive strength is defeasible. - CORRECT ANSWER - True. To say that inductive
strength is defeasible is to say that adding new premises can turn a strong inductive argument
into a weak inductive argument. That is possible when the argument is not valid. The classic
example is that many people observed thousands of swans throughout six continents and
,concluded that all swans are white. That was a decently strong inductive argument, because their
sample was very large and diverse. But then they learned about black swans in Australia. As soon
as they had that new information in their premises, they ceased to have any reason at all to
believe that all swans are white.
Inductive arguments always have general conclusions. - CORRECT ANSWER - False.
Here's an inductive argument with a particular conclusion: "Most birds can fly, and this owl is a
bird, so probably this owl can fly." Here's another: "The best explanation of the evidence at the
crime scene is that Richard killed the victim, so Richard probably did kill the victim." Each of
these arguments is invalid and defeasible, so they are inductive, even though they do not have
general conclusions.
Deductive arguments always provide more reason for their conclusions than inductive arguments
do. - CORRECT ANSWER - False. Some inductive arguments (such as "The sun has risen
every day for thousands of years, so it will probably rise tomorrow") provide very strong reasons
for their conclusions. Some deductive arguments (such as "There is life on Mars, so there is life
on either Mars or Saturn") provide very little reason for their conclusions, because there is very
little reason for their premises. The former arguments provide more reason for their conclusions
than the latter. Hence, some inductive arguments provide more reason for their conclusions than
some deductive arguments do.
Indicate whether the argument is deductive or inductive. Assume a standard context as described.
Nothing tricky!
Context: You and I want to go for a walk, but it is raining, and we do not want to walk in the
rain. You ask me when I think it will stop raining. Then I say this sentence:
"The sun is coming out, so the rain will probably stop soon." - CORRECT ANSWER -
Inductive.
The word "probably" suggests that this argument is not intended as a valid proof of its
conclusion. When an argument is valid, it is necessary—not just probable—that the conclusion is
true if the premises are true. Thus, if an arguer says only that the conclusion is probably true
given the premises, then that person does not intend the argument to be valid. This makes the
argument inductive.
Indicate whether the following argument is deductive or inductive. Assume a standard context as
described. Nothing tricky!
, Context: Harold is accused of a burglary, but we know him and thought he was a nice person, so
we do not know whether to believe that he is guilty. Then you give this argument.
"If Harold were innocent, then he would not go into hiding. Since he is hiding, he must not be
innocent." - CORRECT ANSWER - Deductive. This argument is valid because its
conclusion can never be false while both of its premises are true. To see this, just try to tell a
coherent story where the premises are all true and the conclusion is false. You can't, so the
argument is valid. Almost all arguments that are valid were intended to be valid. Hence, this
argument was probably intended to be valid. That makes it deductive.
Indicate whether the following argument is deductive or inductive. Assume a standard context as
described. Nothing tricky!
Context: Harold is accused of a burglary. We think that he is not guilty, but we worry that he
might be punished anyway. Then I give this argument.
"If Harold is not innocent, then he will be punished. But he is innocent, so he will not be
punished." - CORRECT ANSWER - Deductive. This argument is not valid, because its
conclusion can be false even if both of its premises are true. Some people are punished by
mistake when they are innocent. Nonetheless, this argument looks like another argument that is
valid (such as this different argument: "If Harold is innocent, then he will not be punished. But
he is innocent, so he will not be punished."). This similarity to a valid argument might make the
argument in our example appear valid. That appearance suggests that the person who gave the
argument in our example intended the argument to be valid. That intention makes the argument
deductive even if it fails to be valid.
Indicate whether the following argument is deductive or inductive. Assume a standard context as
described. Nothing tricky!
Context: I order a cola drink at midnight. You comment that you never drink cola that late at
night, because the caffeine in cola keeps you from sleeping well. I respond with this argument:
"Cola drinks never keep me awake at night. I know because I drank a cola drink just last night
without any problems." - CORRECT ANSWER - Inductive. This argument is not valid and
