Argument Evaluation: The Basics ***Part 1 (50%): State whether the following arguments are: a) deductive or inductive, b) valid, invalid, strong, or weak, c) sound, unsound, cogent, uncogent; and...

Argument Evaluation: The Basics

***Part 1 (50%): State whether the following arguments are: a) deductive or inductive, b) valid, invalid, strong, or weak, c) sound, unsound, cogent, uncogent; and d) indicate the truth values (true or false) of their premises and conclusions.***

1. Constructing the great pyramid at Giza required lifting massive stone blocks to great heights. Probably, the ancient Egyptians had some antigravity device to accomplish this feat.

2. If George Washington was beheaded, then he died. He did die, therefore he was beheaded.

3. Something is morally permissible only if Tim says that it is. Tim says that cheating on homework is wrong. Therefore, cheating on homework is wrong.

4. Americans have been listening to Kanye West for over 200 years now. Probably some people will still be listening to Kanye next week.

5. Since Cedar City is north of St. George and south of Beaver, it follows that Beaver is north of St. George.

6. North Korea’s news agency reported that their paleontologists had unearthed the fossilized remains of unicorns, thus proving that unicorns once roamed earth. [Note: the premise is true.]

7. Since Moby Dick was written by Shakespeare, and Moby Dick is a science fiction novel, it follows that Shakespeare wrote a science fiction novel.

***Part 2 (50%): Answer each of these in a short paragraph.***

8. Imagine that you gave me an argument, and in response I say, “I agree that this is a sound argument. However, I don’t accept its conclusion.” Explain what is wrong with what I just said.

9. Imagine one of your confused classmates asked you, “Can a false argument have a true conclusion?” Help straighten them out and explain what is wrong with the question.

10. Explain whether you think the following argument is invalid, valid, or sound: all physical events are predetermined. If all physical events are predetermined, then there is no free will; and if there is no free will, then we are not responsible for our actions. Therefore, we are not responsible for our actions.

Asked on by koinekid

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pohnpei397 | College Teacher | (Level 3) Distinguished Educator

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In order to answer this question, you must first divide your statements into deductive and inductive statements.  Deductive statements start with premises and then give conclusions based on those premises.  The argument is based on the premises and nothing else.  Inductive statements start with the presentation of some data and go on to try to infer truths that are based on those data.  With those definitions in mind, we can say that #s 2, 3, 5, and 7 are deductive and the others are inductive.  This is because the numbers listed give premises (If Washington was beheaded, he died.  Washington did die) and make conclusions (Washington was beheaded) based on those premises.

Deductive arguments can be valid or invalid.  They are valid if the conclusion must be true so long as the premises are true.  An argument can be valid and still be untrue.  #2 is not valid.  Even if all people who are beheaded die and Washington did die, it does not follow that Washington must have been beheaded.  This is because the first premise does not tell us that people can only die if they are beheaded.  Therefore, this argument is invalid.  The other deductive arguments are all valid.

If a deductive argument is valid, it might be sound.  Any invalid argument is automatically unsound.  An argument is sound if the premises are actually true.  Therefore, #3 is probably not sound because Tim is probably not the sole arbiter of morality.  #7 is clearly not sound because Shakespeare did not write Moby Dick.  #5 may be sound and you would have to consult a map of Utah to determine if it is.

Turning now to the inductive arguments, we can say that they are strong or weak.  This is a little hard to determine at times because we have to determine whether the data given probably lead to the conclusion.  There can be disagreement on this point.  For example, I say that #1 is weak because there is no such thing as an antigravity device.  However, you could argue that the most likely explanation is that aliens gave them the devices, which are now lost to us.  This seems to be stretching things, but it is a matter of opinion.  I would say that #4 is a strong argument but #6 is not because I do not take the North Korean news service as a reliable source of information.

Now we have to find out if these inductive arguments are cogent.  That is, are the premises likely to be true?  Number 1 is cogent in that the construction of the pyramid did require lifting rocks.  Number 4 is not cogent because people have not been listening to Kanye West for 200 years.

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