SSH 105 TEST #2 QUESTIONS & ANSWERS
What are the two questions we should ask when evaluating an argument? - Answers -
1. Are its premises true?
2. Is the argument valid?
These questions are INDEPENDENT of each other.
What are the two features an argument should have? - Answers -Ideally, an argument
should have two features. It should have true premises and its premises should support
its conclusion. Whether the premises in an argument are true has NOTHING to do with
whether they support its conclusion.
What makes an argument valid? - Answers -An argument is valid if and only if it is not
possible for the premises to be true and the conclusion false.
- if all the premises were true, the conclusion would have to be true too.
- the conclusion logically follows from the premises.
Two things that are really nice about validity from a critical thinking point of view: -
Answers -- Every argument is either valid or not valid. There's no in between.
- We can figure out whether an argument is valid or not mostly just by thinking about it
Validity Test - Answers -To test an argument for validity, first suppose that the premises
were true. (imagine a world where the premises are true)
Then ask: could the conclusion still be false? (could the conclusion be false in that
imagined world?)
- If YES, then the argument is not valid.
(The truth of the premises WOULD NOT be sufficient for that of the conclusion)
- If NO, then the argument is valid.
(The truth of premises WOULD be sufficient for that of the conclusion)
Example using validity test - Answers -"Justin Trudeau is Prime Minister of Canada and
every Prime Minister of Canada is Canadian. So, Justin Trudeau is a Canadian."
- Premise 1 is true (Justin Trudeau is prime minister of Canada)
- Premise 2 is true (every prime minister of Canada is Canadian)
- Conclusion is true as well (Justin Trudeau is a Canadian)
- This argument is VALID, if the premises are true the conclusion would have to turn out
to be true too
- there is no universe where Trudeau is prime minister and all prime ministers are
Canadian, but he is not a Canadian. (it doesn't make any sense)
Invalid with true premises and a true conclusion - Answers -- If I'm hungry, then I'll eat
pasta. I am about to eat pasta. So, I'm hungry.
- I studied all night. I understood the material. So, I passed the test.
, Valid with true premises and a false conclusion - Answers -IMPOSSIBLE!!! It's the
exact opposite of the definition of validity.
- If all the premises were true, the conclusion would have to be true too.
Valid with false premises and a true conclusion - Answers -- Jon Stewart is a Martian
and every Martian hosts a TV show, so Jon Stewart hosts a TV show.
- Earth is flat. All planets are flat. So earth is a planet!
Valid with true premises and a true conclusion - Answers -- Ed Sheeran is human and
all humans have parents, so Ed Sheeran has parents.
- Justin Trudeau is prime minister of Canada, and all prime ministers of Canada are
Canadian, so Justin Trudeau is Canadian.
Valid with false premises and a false conclusion - Answers -- Shawn Mendes is a
Martian, and all Martians are prime ministers. So, Shawn Mendes is prime minister.
- All humans are blue, all blue things smell like apples, therefore all humans smell like
apples.
Invalid with true premises and false conclusion - Answers -- Shawn Mendes is a man,
and all men are humans, so Shawn Mendes is the Prime Minister of Canada.
Invalid with false premises and true conclusion - Answers -- Planets are flat. Planets do
not spin. So, earth is a planet.
Missing premises - Answers -If an argument is not valid, then it is not a good argument.
But sometimes, a person will give an argument but leave out a crucial premise. The
argument, as they wrote it, is not valid. But, by adding a premise, it can be turned into a
valid argument. We can call it a missing premise.
Examples:
- Miranda really wants her plants to thrive, so it will probably rain today.
- It has not rained in many days; so it will probably rain today.
- The bridge is too expensive. We should not build it.
How to turn invalid argument to valid one - Answers -Simply add to the argument as a
new premise a conditional whose antecedent is the existing premise and whose
consequent is the conclusion.
Example:
- Miranda really wants her plants to thrive, and {if she really wants her plants to thrive,
then it will rain today}, so it will rain today.
- It has not rained in many days, and {if it has not rained in many days, then it will rain
today}, so it will rain today.
- The bridge is too expensive, and {if it is too expensive, then we should not build it}; so,
we should not build the bridge.
Principle of Charity - Answers -When evaluating someone's argument, try to turn it into
a valid argument. That way, you can focus on whether the premises (including the one
What are the two questions we should ask when evaluating an argument? - Answers -
1. Are its premises true?
2. Is the argument valid?
These questions are INDEPENDENT of each other.
What are the two features an argument should have? - Answers -Ideally, an argument
should have two features. It should have true premises and its premises should support
its conclusion. Whether the premises in an argument are true has NOTHING to do with
whether they support its conclusion.
What makes an argument valid? - Answers -An argument is valid if and only if it is not
possible for the premises to be true and the conclusion false.
- if all the premises were true, the conclusion would have to be true too.
- the conclusion logically follows from the premises.
Two things that are really nice about validity from a critical thinking point of view: -
Answers -- Every argument is either valid or not valid. There's no in between.
- We can figure out whether an argument is valid or not mostly just by thinking about it
Validity Test - Answers -To test an argument for validity, first suppose that the premises
were true. (imagine a world where the premises are true)
Then ask: could the conclusion still be false? (could the conclusion be false in that
imagined world?)
- If YES, then the argument is not valid.
(The truth of the premises WOULD NOT be sufficient for that of the conclusion)
- If NO, then the argument is valid.
(The truth of premises WOULD be sufficient for that of the conclusion)
Example using validity test - Answers -"Justin Trudeau is Prime Minister of Canada and
every Prime Minister of Canada is Canadian. So, Justin Trudeau is a Canadian."
- Premise 1 is true (Justin Trudeau is prime minister of Canada)
- Premise 2 is true (every prime minister of Canada is Canadian)
- Conclusion is true as well (Justin Trudeau is a Canadian)
- This argument is VALID, if the premises are true the conclusion would have to turn out
to be true too
- there is no universe where Trudeau is prime minister and all prime ministers are
Canadian, but he is not a Canadian. (it doesn't make any sense)
Invalid with true premises and a true conclusion - Answers -- If I'm hungry, then I'll eat
pasta. I am about to eat pasta. So, I'm hungry.
- I studied all night. I understood the material. So, I passed the test.
, Valid with true premises and a false conclusion - Answers -IMPOSSIBLE!!! It's the
exact opposite of the definition of validity.
- If all the premises were true, the conclusion would have to be true too.
Valid with false premises and a true conclusion - Answers -- Jon Stewart is a Martian
and every Martian hosts a TV show, so Jon Stewart hosts a TV show.
- Earth is flat. All planets are flat. So earth is a planet!
Valid with true premises and a true conclusion - Answers -- Ed Sheeran is human and
all humans have parents, so Ed Sheeran has parents.
- Justin Trudeau is prime minister of Canada, and all prime ministers of Canada are
Canadian, so Justin Trudeau is Canadian.
Valid with false premises and a false conclusion - Answers -- Shawn Mendes is a
Martian, and all Martians are prime ministers. So, Shawn Mendes is prime minister.
- All humans are blue, all blue things smell like apples, therefore all humans smell like
apples.
Invalid with true premises and false conclusion - Answers -- Shawn Mendes is a man,
and all men are humans, so Shawn Mendes is the Prime Minister of Canada.
Invalid with false premises and true conclusion - Answers -- Planets are flat. Planets do
not spin. So, earth is a planet.
Missing premises - Answers -If an argument is not valid, then it is not a good argument.
But sometimes, a person will give an argument but leave out a crucial premise. The
argument, as they wrote it, is not valid. But, by adding a premise, it can be turned into a
valid argument. We can call it a missing premise.
Examples:
- Miranda really wants her plants to thrive, so it will probably rain today.
- It has not rained in many days; so it will probably rain today.
- The bridge is too expensive. We should not build it.
How to turn invalid argument to valid one - Answers -Simply add to the argument as a
new premise a conditional whose antecedent is the existing premise and whose
consequent is the conclusion.
Example:
- Miranda really wants her plants to thrive, and {if she really wants her plants to thrive,
then it will rain today}, so it will rain today.
- It has not rained in many days, and {if it has not rained in many days, then it will rain
today}, so it will rain today.
- The bridge is too expensive, and {if it is too expensive, then we should not build it}; so,
we should not build the bridge.
Principle of Charity - Answers -When evaluating someone's argument, try to turn it into
a valid argument. That way, you can focus on whether the premises (including the one
