Student Question
Are the following arguments deductive or inductive, valid, invalid, strong, weak, sound, unsound, cogent, uncogent; and indicate the truth values of their premises and conclusions?
Quick answer:
Arguments 2, 3, 5, and 7 are deductive; the rest are inductive. Deductive arguments are valid if conclusions necessarily follow from true premises. Argument 2 is invalid; 3, 5, and 7 are valid but unsound due to false premises. Inductive arguments are strong if conclusions are likely based on premises. Argument 1 is weak but cogent; 4 is strong but uncogent due to a false premise; 6 is weak and uncogent. Validity and soundness depend on factual premises.
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...
Unlock
This Answer NowStart your 48-hour free trial and get ahead in class. Boost your grades with access to expert answers and top-tier study guides. Thousands of students are already mastering their assignments—don't miss out. Cancel anytime.
Already a member? Log in here.
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.
References