Understanding Arguments: Identifying Conclusions, Premises, and Validity - Prof. Mikhail V, Study notes of Introduction to Philosophy

Download Understanding Arguments: Identifying Conclusions, Premises, and Validity - Prof. Mikhail V and more Study notes Introduction to Philosophy in PDF only on Docsity! Arguments An argument is a statement or a series of statements intended to establish a conclusion. Or, as previously explained, an argument is a piece of reasoning wherein some claims (the premises) are presented in support of some other claim (the conclusion). An argument’s conclusion is that which the argument seeks to prove. The statements presented in support of the conclusion are called premises. When presented with an argument, always begin by determining its conclusion. Sometimes this is very easy, like in the following case: “We need to move to a government run health care system. We have too many people without health insurance and medical costs are spiraling out of control.” Sometimes not enough information is given to determine the conclusion, such as here: “Jim is a jerk. He never returns my phone calls.” Sometimes the conclusion is not explicitly stated but is nevertheless evident: “The Petro Pick-Me-Up is the most powerful vacuum on the market. It never breaks. And, if you act now, you can get one for just half its retail price. But wait! If you order one in the next 10 minutes we’ll even throw in a framed photograph of the Petro in action at no additional cost! This photograph is not available in stores, and it can be had only through this exclusive one-time offer.” As we saw last time, it’s not always clear whether some passage is an argument, and even if it is an argument it is not always clear what it is saying. This is due in part to vagueness in the language (especially the written language) and to the fact that people often don’t realize that their words can be interpreted in different ways. When philosophers confront unclear passages, they employ a principle of charity, which says that we should interpret arguments in a way that makes our opponent’s views as plausible and defensible as possible. Consider: Senator A: “I support free speech rights, and that’s why I’m against laws that would criminalize pornography.” Senator B: “Well, if you’re such a big fan of free speech, then I suppose you see nothing wrong with falsely accusing your enemies of being child rapists, of encouraging people to assassinate political leaders, or of yelling “fire” in a crowded theater!” Here B is both misrepresenting A’s argument and he is being deeply uncharitable in his interpretation of A’s views on free speech. Indeed, here B has set up a straw man. Analyzing Arguments Good arguments have good reasoning and true premises. These two features are independent of each other. Arguments can have good reasoning but false premises and they can have true premises but bad reasoning. Here is an argument with true premises but bad reasoning: (1) All dogs are mammals (2) All cats are mammals. (3) Therefore, all dogs are cats. The reasoning is bad here not because the conclusion is false, but because the premises don’t support the conclusion. If an argument is a bad one, it can be bad for only two reasons: either it has one or more false premises, or it has bad reasoning (or both).* Assessing reasoning To test the quality of an argument’s reasoning, ask yourself whether the truth of its premises would guarantee the truth of its conclusion. When an argument’s premises, if true, would guarantee the truth of its conclusion, we say that the argument is valid. When an argument is both valid and has true premises, we say that it is sound. A valid argument is such that were its premises to be true, its conclusion would have to be true. Technical definition of validity: an argument is valid if it is impossible for its premises to be true and its conclusion to be false. The following argument is valid but not sound: (1) All tigers can sing show tunes. (2) Anything that can sing a show tune can stand on its head. (3) Therefore, all tigers can stand on their heads. (a) Water boils at 100 degrees Celsius. (b) The Vietnam war ended in 1975. (c) Our government spends less than one percent of its budget on foreign aid. (d) George Bush is the tallest president the U.S. has ever had. The following are normative claims: (a) You should drink water every day. (b) The Vietnam war should have ended in 1968. (c) Our government needs to spend more money on foreign aid. (d) George Bush is a bad president. (e) Fred ought to get a college education. The following are both descriptive and normative claims: (a) Bill is a generous person. (b) Fresh spinach is so nutritious. (c) Sally isn’t the sharpest tool in the shed. (d) Drinking eight cups of water a day is good for your health. Bearing in mind the normative/descriptive distinction, try to figure out the conclusions of the following arguments: Jill, the hike you’ve planned for us is 25 miles long over some very hilly terrain. It’ll be 100 degrees for most of the day and there is little tree cover to protect us. There is no cell phone reception, and, if anything should happen, there won’t be anyone within reach who could help us. Why can’t I borrow your car? You’re not using it, and you know that if anything happens to it I will take full responsibility. Why shouldn’t I cheat on my wife? Nobody takes wedding vows seriously anymore, and she’d probably never find out anyway. Assumptions Most arguments contain assumptions. An assumption is an unstated premise that is needed to make the argument valid. When you reconstruct an argument (i.e. clearly label its premises and conclusions), you should make these assumptions explicit. Consider: Of course he’s a Republican. After all, he’s from Texas. It looks like Stacy put on some weight. And did you notice how, at dinner, she refused wine and ate only bread? I bet she’s pregnant. Pornography communicates a message, so it is a form of speech, so it shouldn’t be illegal. In a valid argument, the conclusion is just the premises put together. There can’t be anything in the conclusion that isn’t already in the premises. This means that you’ll often have to add premises to an argument in order to make it valid, where these added premises “link up” the other premises with the conclusion. Reconstructing Arguments Try to reconstruct the following arguments, making note of any assumptions. “I’m disgusted by the thought of homosexual sex. It’s simply unnatural. Nature intended for men to sleep with women and women with men, not for women to sleep with women or men to sleep with men!” (Hint: this argument contains a hidden premise) (1) Homosexuality is unnatural. (2) (Assumption) Everything that’s unnatural is wrong. (C) Therefore, homosexuality is wrong. Child: Will the sun rise in the east tomorrow? Father: Of course it will. It rose in the east today, yesterday, and the day before. In fact, there has never been a day when the sun didn’t rise in the east. (1) The sun has always risen in the east. (2) The future will resemble the past – things that always happened in the past will also happen in the future, in exactly the same way. (C) Therefore, the sun will rise in the east tomorrow. Argument Forms Consider the following argument: (1) Bill is older than Nancy. (2) Nancy is older than Joe. (3) Therefore, Bill is older than Joe. Notice that this argument’s validity doesn’t depend on the content of its premises. We could switch all of the names around and the argument would still be valid. This means that an argument’s validity stems not from what its premises say but how they say it. It stems not from their content but from their form or structure. To find an argument’s form, just substitute letters (i.e. variables) for the particular claims contained in the premises, leaving undisturbed the quantifiers (e.g. all, some, none) and the logical operators (e.g. and, if..then, not, or). Make sure to use to same letters for the same statements. The form of the above argument is: (1) X is older than Y. (2) Y is older than Z. (3) Therefore, X is older than Z. This is a valid argument form. No matter what statements you insert for X, Y, and Z, the argument will be valid. Validity is a feature of an argument’s form rather than its content. When determining whether an argument is valid, we ignore its content and just look at its form. We ask whether its “parts” logically entail the conclusion. Consider another example: (1) If Bill thinks that Heather is beautiful, then he should get his vision checked. (2) Bill thinks that Heather is beautiful. (3) Therefore, Bill should get his vision checked. This argument has the following form: (1) if P then Q (2) P (3) Therefore, Q This too is a valid argument form. You can tell whether an argument form is valid by seeing if it is possible to find a “counterexample” to it. A counterexample involves showing that that form allows you to move from true premises to a false conclusion. For instance, consider this argument form: (1) If P then Q (2) Not P (3) Therefore, not Q The counterexample: (1) If Bill Jones is a student in this class, then he is a VCU student. (2) Bill Jones is not a student in this class. (3) Therefore, Bill Jones is not a VCU student. Worksheet Answers (1) Harvard was the best college in 1970. (2) Harvard is much better today than it was in 1970. (C) Therefore, Harvard is still the best college. (C2) Therefore, the shepherd is damned. (1) Senator: Yes, I accepted campaign contributions from Halliburton, and yes, they had a contract pending before my committee. But there is nothing illegal about that, so I did nothing wrong. (1) I did nothing illegal. (A) One can do something wrong only if one does something illegal. (C) Therefore, I did nothing wrong. (2) Student: Why shouldn’t I buy a term paper? I’m an English major assigned a paper on physics, which I know nothing about and don’t want to know anything about. (1) If a non-major is assigned a term paper about which he has no interest, it isn’t wrong for him to buy it. (2) I am an English major who has been assigned a term paper in physics, about which I have no interest. (C) Therefore, it isn’t wrong for me to buy this term paper. (3) Louisiana State Rep. Carl Gunter: I fully support the new bill which would criminalize abortion in cases of incest. After all, inbreeding is how we get championship racehorses. (1) Incest produces good results with horses. (A) Whatever produces good results with horses should produce good results with people. (C1) Therefore, incest should produce good results with people. (4) If incest produces good results with people, then people shouldn’t be permitted to have abortions in cases of incest. (C2) Therefore, abortion should not be permitted in cases of incest. (4) People cannot be motivated by their beliefs alone – only desires can motivate. However, people can be motivated by their moral judgments. For instance, the other day, I decided that giving money to the homeless is the right thing to do, and I did it. So it follows that moral judgments cannot be beliefs. (1) Beliefs alone can never motivate. (2) Moral judgments can motivate. (3) Therefore, moral judgments are not beliefs.