PHI 103 Informal Logic

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timer Asked: May 4th, 2017

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Mark as UnreadWeek 2 Discussion 2 Topic for the ClassInstructor Van Horn Email this Author4/22/2017 5:29:50 PM

We have learned this week about deductive reasoning, including what it takes for an argument to be valid. This discussion allows us to get more practice with the concept through making arguments valid. Below you will see a list of arguments. These arguments are not presented in standard form, and each is missing a premise that would be necessary to make it valid. Your tasks will be to put the argument into standard form and add the missing premise that would validly link the premises to the conclusion.

Prepare: To prepare to respond to this prompt, reread the section from Chapter 2 of our book titled “Extracting Arguments in Standard form,” all required portions of Chapters 3 and 4, as well as the guidance and required media for this week. Further assistance in the filling missing premises can be gained from watching the video Constructing Valid Arguments.

Reflect: Look at the list of argument options below. Choose an argument that has not yet been chosen by any of your classmates. Think through the reasoning and determine what premise is (or premises are) missing that would be needed to make the argument valid. You might also consider challenging yourself by choosing from the more difficult examples in the list (at the bottom).

Choose from the following list of argument options.

Flipper is a dolphin, so Flipper is a mammal.

Football is dumb because it is a waste of time.

If he loved you he would have shown up on time with flowers. He must not love you.

All mammals bear live young, so dragons are not mammals.

Abortion kills a human being, therefore abortion is wrong.

He broke the record for rushing yards in a game on that last play. Therefore he holds the record.

He won the election. So he will be the next governor.

He won’t go to the wedding since he doesn’t like mushy stuff and weddings are mushy.

I can’t go to the movies with you – I have a test tomorrow and I have to study.

Mike loves pickles. Pickles come from cucumbers. Therefore Mike loves cucumbers.

You shouldn’t go out with that guy. He rides a motorcycle and goes to bars.

Capital punishment is wrong because it is killing and it doesn’t save anyone’s life.

You shouldn’t use drugs because they are addictive and can ruin people’s lives.

To fix your care you will need money. However, to have money you have to have money. It appears that you need to get a job.

To go to the movie you have to have a ticket. To buy a ticket you must pay money. Thus, to go the movie you must pay money.

If you don’t do your chores then you can’t have any dessert. You really like dessert, so you will certainly do your chores.

You will get an A if you study hard and always come to class. You came to class every time and studied. You are bound to get an A.

Julie is allergic to gluten. So she won’t be having any bread.

Only women can have babies, so women are more important to the survival of the species.

If I wear that cologne then women will love me. I bought that cologne, so women are going to love me.

I can’t go to the party because there will be alcohol there, and I am a Mormon.

You shouldn’t force me to wear a seat belt because that would violate my rights.

In order to buy a car you will need money. But to have money you need to get a job. But to go to a job you will need to be able to get to work. So you will not be able to buy a car.

Capital punishment kills a human being. It is wrong to kill a human being except in self-defense. So capital punishment is wrong.

You shouldn’t tell someone to do something unless you would be willing to do it yourself. You’ve never gone to war. So you shouldn’t vote for others to go to war.

If you talk to Mike about politics then he will yell at you. If he yells at you then you will be hurt and it will damage your friendship. Therefore, you shouldn’t talk to Mike about politics.

Either the maid or the butler did it. For the butler to have done it he would have had to have been at the mansion yesterday. The butler was away all day yesterday. So, the maid did it.

If the maid was guilty then she would have had to been at the scene during the crime. However, she was seen a mile away only minutes before the crime, and she has no car. She must be innocent.

It is always wrong to kill a human being unless it is necessary to save somebody’s life. Abortion kills a human being. So abortion is wrong unless the mother’s life is in danger due to the pregnancy.

Government intervention is justified if it is necessary to protect the welfare of the people and does not violate anyone’s constitutional rights. Therefore, government intervention is justified in this specific case because it is necessary to protect the welfare of the people.

Write: In your original post, be sure to include the entire original argument, in standard form, with your own added premise (or premises) in bold. After you have presented the argument, include a description of how the conclusion logically follows from the premises. Include also a reflection on whether it seems that the missing premise(s) is likely to be true (in the context). Would there be any way to fix the argument so that it is valid and has all true premises?


Guided Response: Read the reflections of your classmates and analyze the arguments that they have presented, paying close attention to how the conclusion follows from the premises. In particular, if you believe that their argument is still technically invalid, explain a way in which it would be possible for the premises to be true and the conclusion false. If you think that their argument is valid, then address the question of whether the premises all seem to be true and how it might be improved. If someone presents such a suggestion for your own argument, then respond by attempting to revise the argument so that it is valid and has all true premises.

example; How to Construct a Valid Main Argument 1. State your (tentative) conclusion. Let’s assume that you have chosen your topic and you have a sense of your position on it (though it can be refined as you develop your argument). Suppose, for example, that your topic is the use of elephants in circuses, and suppose you think that it is wrong. This (or some version of it) will be the conclusion of your argument. We just need the premises to get to it. Here is where our argument stands: P1: ? P2: ? C: It is wrong to use elephants in circuses. 2. Ask yourself why it is true. List that reason as a premise. Next, ask yourself why it is wrong? It would not be a bad idea to do a little research at this point so that your reason is more informed. In our example, it might be that the elephants have to live their lives in confinement. This reason is a premise: P1: Putting elephants in circuses requires them to live their lives in confinement. C: Therefore, putting elephants in circuses is wrong. 3. Find another premise that links the premise to the conclusion. We now need another premise to link the premises to the conclusion. In general, if your conclusion has this form: P1: X is A P2: ? C: X is B Then the simplest premise to add to make it valid is “All As are Bs.” Alternatively, if the argument has the form P1: X is A P2: ? C: X is not B Then the simplest missing premise is “No As are Bs.” 4. Determine if the added premise is true. If it has exceptions then you will need to modify it so that it is true. The simplest missing premise is not always the best one, but it is a good place to start. In our example, the simplest missing premise would be “Anything that requires elephants to live their lives in confinement is wrong.” We now ask: Is this premise true? If so then your argument may be sound. Here it is: P1: Putting elephants in circuses requires them to live their lives in confinement. P2: Anything that requires elephants to live their lives in confinement is wrong. C: Therefore, putting elephants in circuses is wrong. However, in many cases, the universal statement “All As are Bs” is too general, and it has many exceptions. These exceptions may mean that the statement is false, so the argument would be unsound. To fix it, it will not do simply to put in the word “usually.” The reason is that it will make the argument invalid. Suppose you put it in the premise, then we have to put it in the conclusion too: P1: X is A P2: As are usually B C: X is usually B The trouble is that the argument is still invalid. How do we know that the X is not one of the types of As that are not B? Here would be an example to show why it is invalid: P1: People from Hungary are human. P2: Humans do not usually speak Hungarian. C: People from Hungary do not usually speak Hungarian. That shows that the form is not valid. To avoid this problem, we may need something more specific than adding ‘usually.’ We have to figure out a principle that explains those circumstances in which the statement is true. In our example, the premise “Anything that requires elephants to live their lives in confinement is wrong” would imply that zoos are wrong as well. Perhaps you feel that zoos are wrong as well. In that case you can stick with the premise as is and defend it against that potential objection. Another possibility is that you think that zoos are not wrong, but then you will have to come up with a difference between zoos and circuses that makes one acceptable but not the other. One possible difference is that circuses require ‘extreme’ confinement because circus elephants spend the majority of their lives on a tiny chain, whereas good zoos give them more room to roam. In that case, you could change your premise to this one: P1: Putting elephants in circuses requires them to live their lives in extreme confinement. However, if we modify that premise alone, then the argument will be invalid because that premise no longer matches the second premise, which brings us to our next step: 5. Modify the other premises so that the wording matches the modification so that your argument is valid again. In this case, a simple modification of P2, to match the change in P1 will do the trick: P2: Anything that requires elephants to live their lives in extreme confinement is wrong. C: Therefore, putting elephants in circuses is wrong. Notice that the word ‘extreme’ has to be placed in both premises so that they match and lead logically to the conclusion. Premises of valid arguments form links in a chain that lead logically to the conclusion. If you have a premise that says that X is A, B, and C, and you want that X is D, then you need a premise that links the exact wording of A, B, and C to D, as follows: P1: X is A, B, and C P2: Anything that is A, B, and C is D C: Therefore, X is D In this way, the link of the chain is solid, linked by the logical form of the argument. There is yet another way to change the argument so that it is valid. Another possible difference between circuses and zoos is that you may feel that zoos serve an important purpose, whereas circuses do not. If that is the case, then your change to the moral premise might look like this: P1: Putting elephants in circuses requires them to live their lives in confinement. P2: Anything that requires elephants to live their lives in confinement is wrong unless it serves an important purpose. C: Therefore, putting elephants in circuses is wrong. This argument, however, is invalid. Do you see why? 6. Add any premises necessary to get logically to the conclusion in the new version. We need another premise. We don’t know that the conclusion is true unless we know that circuses do not serve an important purpose. Here would be the new argument: P1: Putting elephants in circuses requires them to live their lives in confinement. P2: Anything that requires elephants to live their lives in confinement is wrong unless it serves an important purpose. P3: Putting elephants in circuses do not serve an important purpose. C: Therefore, putting elephants in circuses is wrong. 7. Determine if all of the premises are true and if the argument is valid. Are you satisfied with the argument? Carefully double check its validity and the truth of each premise. If there is a possible way to make the premises true and the conclusion false, then the argument is invalid. Return to step 3 and repeat the process. If there is a premise that is not quite true then the argument, even if valid, is unsound. Return to step 4 and repeat the process. This process can take quite a bit of versions to get an argument just right. 8. Consider possible objections to your argument and possible ways to strengthen it. In our case, for example, the phrase “important purpose” is vague. One might consider the role of elephants in circuses to be an important purpose. This does not mean that our idea was wrong, only that it may need to be revised further. Perhaps what the argument really meant is that the degree of suffering of the severely confined elephants is not justified by the added degree of pleasure to circus goers of seeing elephants there. This insight could be incorporated into the argument. An improved version of the argument then might look like this: P1: Putting elephants in circuses requires them to live their lives in confinement. P2: Anything that requires elephants to live their lives in confinement is wrong unless it serves a purpose that outweighs the suffering involved. P3: Putting elephants in circuses do not serve a purpose that outweighs the suffering involved. C: Therefore, putting elephants in circuses is wrong. One could even go further and wonder why the argument is limited to elephants. Perhaps one could say the same about certain other species of animals as well. If one wanted to strengthen the argument, the premise 2 could be modified to include a broader class of ‘highly intelligent animals’, as follows: P1: Putting elephants in circuses requires them to live their lives in confinement. P2: Anything that requires highly intelligent animals to live their lives in confinement is wrong unless it serves a purpose that outweighs the suffering involved. P3: Putting elephants in circuses do not serve a purpose that outweighs the suffering involved in their lives of confinement. C: Therefore, putting elephants in circuses is wrong. 9. Triple check the soundness of the argument, and repeat the steps as many times as necessary to get it just right. In this case, though premise 2 is stronger (entailing similar conclusions about dolphins, orcas, chimpanzees, and perhaps other types of animals as well), the argument has become technically invalid. Do you see why? To make it valid again, we simply need a new premise to connect the wording “’highly intelligent” to elephants, resulting in: P1: Putting elephants in circuses requires them to live their lives in confinement. P2: Anything that requires highly intelligent animals to live their lives in confinement is wrong unless it serves a purpose that outweighs the suffering involved. P3: Putting elephants in circuses do not serve a purpose that outweighs the suffering involved. P4: Elephants are highly intelligent animals. C: Therefore, putting elephants in circuses is wrong. Perhaps the reader finds this to be an acceptable argument for use in paper. However, there will still be people who disagree. Think about some ways in which people might disagree and see if the argument can be further strengthened (while remaining logically valid). It is a very challenging process, but it is one that at the end can actually make you smarter! Summary of the Steps In summary, here are the steps to follow: 1. State your (tentative) conclusion. 2. Ask yourself why it is true. List that reason as a premise. 3. Find another premise that links the premise to the conclusion. Hint: If your premise is “X is A”, and your conclusion is “X is wrong” then you could use “All As are wrong.” 4. Determine if the added premise is true. If it has exceptions then you will need to modify it so that it is true. Hint: Do not merely add a word like “usually,” but try to determine the principle that makes a difference between the cases that are wrong and that are not wrong (or whatever word your are employing). Add this principle to the premise so that it is true. 5. Modify the other premises so that the wording matches the modification (e.g. adding the word ‘extreme’ in the above example) of the moral premise and so that your argument is valid again. 6. Add any premises necessary to get logically to the conclusion in the new version (e.g. adding the premise that circuses don’t serve an important purpose in the above example). 7. Determine if all of the premises are true and if the argument is valid. If not then return to step four and repeat the process until it is valid and has all true premises (true as far as you can tell). 8. Consider possible objections to your argument and possible ways to strengthen it. If you can make your argument stronger, while remaining sound then go for it. You are done (for now) when you have an argument that says what you want it to say, and has all true premises, and has a logically valid form of reasoning. Great work; you should feel smarter! 9. Triple check the soundness of the argument, and repeat the steps as many times as necessary to get it just right. Note: This is not the only way to create valid arguments, however, this process is very effective for creating valid arguments with normative conclusions. For further instruction, see the supplemental document: Principles of valid arguments. Examples: Finally, here are some other examples of valid arguments that can result from such a process: Any action in which all of the participants are voluntary and that does not violate anyone’s rights is ethically permissible. All of the participants in boxing are voluntary. Boxing does not violate anyone’s rights. Therefore, boxing is ethically permissible It is foolish to do things with one’s money that have a known likelihood of leading to a net financial loss. Gambling is something that people do with their money. Gambling has a known likelihood of leading to a net financial loss. Therefore, it is foolish to gamble. The government should never do things that prevent people from becoming fully informed citizens, unless it is necessary for public security. Banning books prevents people from becoming fully informed citizens. Therefore, the government should never ban books unless it is necessary for public security. Using illegal drugs is addictive and does not have long term benefits that outweigh the risks. Things that are addictive have the potential to ruin one’s life. One should not do things that have the potential to ruin one’s life unless they have long term benefits that outweigh their risks. Therefore, one should not use illegal drugs

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