Philosophy 1010 Class #4 Title: Introduction to Philosophy Instructor: Paul Dickey E-mail Address: pdickey2@mccneb.edu Today: Submit your two-page Socratic Dialogue “play.” Submit your Movie Mini-essay. Assignments for 10/2/13: 1 Read Velasquez, Philosophy: A Text With Readings, Chapter 3, Sections 3.1 – 3.5 2. Re-read Logic Appendix. Send me an email and ask specifica questions on what you don’t understand. (I expect an email from everyone.) 2. Exercises at end of Logic Reading Assignment (page 70)

Two Kinds of Good Arguments 1) A good deductive argument is one in which if the premises are true, then the conclusion necessarily (I.e. has to be) true. Such an argument is called “valid” and “proves” the conclusion. For example – Julie lives in the United States because she lives in Nebraska. All men are mortal. Socrates is a man. ____ Socrates is mortal. A sound argument is a valid, deductive argument in which the premises are in fact true.

How Do Premises Support Conclusions? For a Deductive argument, premises prove a conclusion based on the logical form of the statement. Consider the argument: (P1) If it’s raining outside, the grass is wet.         (P2) It’s raining outside.             _________________________         (Conclusion) The grass is wet. In this case, the premises support the conclusion fully simply by what the premises say. It would be a contradiction to suggest that the conclusion is false but the premises are true.

A. Categorical Arguments Deductive Arguments: A. Categorical Arguments Categorical Logic is logic based on the relations of inclusion and exclusion among classes. That is, categorical logic is about things being in and out of groups and what it means to be in or out of one group by being in or out of another group. The following is a categorical syllogism: (Premise 1) All Americans are consumers. (Premise 2) Some consumers are not Democrats. (Conclusion) Some Americans are not Democrats. 4

B. Hypothetical Arguments “If it’s raining outside, the grass is wet. It’s raining outside. Thus, the grass is wet.” We often use variables to represent statements to analyze arguments. In this case, say for example, R = It’s raining outside; W = The grass is wet. and “->” as if/then, 1) Thus we have an argument of the form: R -> W R _____ W This is the rule of modus ponens. 

“If it’s raining outside, the grass is wet. The grass is not wet “If it’s raining outside, the grass is wet. The grass is not wet. Thus, it is not raining.” R -> W ~W _____ ~R This is the rule of Modus Tollens.

C. Disjunctive Arguments “Either it’s raining outside or the grass is dry. The grass is not dry. Thus, It’s raining outside.” A before, we use variables to represent statements to analyze arguments. In this case, say for example, R = It’s raining outside; D = The grass is dry.” and “v” as either/or” and “~” as not. 1) Thus we have an argument of the form: R v D ~D _____ R

D. Chain Arguments “If it’s raining outside, the grass is wet. If the grass is wet, then our toddler will slip and fall. Thus, if it is raining outside, our toddler will slip and fall.” R -> W W -> S _____ R -> S

Ten Minute Break!

Two kinds of good arguments, cont. 2) A good inductive argument is one in which if the premises are true, then the conclusion is probably true, but not always. The truth of the premises do not guarantee the truth of the conclusion. Such an argument is called “strong” and supports the conclusion. For example: Craig lives in Nebraska and he loves football, so he is a Nebraska Cornhusker fan. If offered to me before class today, I would have made a bet with my wife that each of you would sit in the same seat in class that you did last Wednesday. If she would have taken the bet, would I have won more money than I would have lost?

How Do Premises Support Conclusions? For an Inductive argument, premises support (never prove) a conclusion based on how good the premises provide evidence for the conclusion. Consider the argument: (P1) If it’s raining outside, the grass near the house gets wet when the wind is not blowing strongly from the North (which doesn’t often occur). (P2) It’s raining outside. _________________________ The grass near the house is wet. Note: It would not be a contradiction to suggest that the conclusion is false but the premises are true.

How Does Sometimes Our Thinking Crash?

Rhetoric We are often influenced by rhetoric, language that is psychologically persuasive but does not have pertinent logical force. There are many kinds of rhetorical deceptions or “devices”, including: hyperbole, proof surrogates, image rhetoric, and euphemisms

Subjectivism The view that “one opinion is as good as another,” or “whatever is true is only what you think is true” is subjectivism. For some things, this makes sense. Does Miller taste great? To tell if something is subjective, ask yourself: “If Curtis says “A” is true and Alicia says “A” is not true, can they both be right? One cannot give an argument either for or against a subjective position. Now, do you really believe that whether God exists is subjective? What about other philosophical issues? Is what is real dependent on what your friend thinks it is? When you reach out to catch a ball, do you “really” believe whether your friend believes the ball is not real matters?

Logical Fallacies are “Screw-ups” in Reasoning Logical Fallacies can be Formal or Informal. A formal fallacy is something like: All mothers are women. Janice is a woman. Thus, Janice is a mother. This is a formal fallacy because its logical form is invalid. An informal fallacy is something like: Janice believes in God. Janice is not good at algebra. Thus, God does not exist. That is, an informal fallacy are errors in logic usually because the “premises” of the argument either are ambiguous or irrelevant to the claim.

Informal Fallacies often occur when the purported premise is not even relevant. (These are known as “the fallacies of relevance”) They include: Appeal to Emotion/Authority Ad Hominems Argument from Ignorance Begging the Question Wishful Thinking

The Ad Hominem Fallacy Maybe the most common of all logical mistakes. The Ad Hominem Fallacy mistakes the qualities of the argument itself with the qualities of the person making the claim. Most Ad Hominem arguments are negative. In an ad hominem, a person attacks the proponent of an argument rather than analyzing the argument itself. http://www.youtube.com/watch?v=9emz5hpxkrw

Misplacing the Burden / Argument from Ignorance The burden of proof in an argument rests on the person making the claim. It is her responsibility to give the premises and the reasons to believe her claim is true. To try to shift the burden of proof onto the person who is listening to your argument and trying to make him show that you are wrong is called misplacing the burden of proof. A particular example of this logical error is the appeal to ignorance which suggests that we should believe something because no one has proven or shown it to be wrong.

Begging the Question Begging the question is assuming as true the claim that is at issue and is to be supported. For example, God exists because the Bible says so and we should believe what the Bible says because it was written by God. Another example: An old gold miner’s joke: One gold prospector asks the other: Why do you get two pieces of gold for every one I get. The second answers “Because I am the leader.” The first then replies but why are you the leader? The second responds: “Because I have twice the gold you do.”

Wishful Thinking Our hopes, desires and personal needs can delude us and make us vulnerable to the fallacy of wishful thinking. We should always be able to recognize when analyzing an argument what we want to believe and be sure that our desires are not overriding our critical thinking and making us come to conclusions simply because of what “we want to believe.” We may want to believe, for example, that God exists so that we might feel more secure or happy. We must thus separate that wish from the reasons that can serve as premises for our claim that God exists. You probably don’t want to believe this, but it is likely true: http://www.scholarspot.com/video/11916/4415/Media-Multitaskers-Pay-Mental-Price

Composition/Division Informal Fallacies also occur when it is not recognized that the purported premise is ambiguous. (These are known as “fallacies of ambiguity”) These include: Equivocation Amphiboly Composition/Division

1. Equivocation: words or phrases change meaning between premises and conclusion. (semantic confusion) All banks are beside rivers. Therefore, the financial institution where I deposit my money is beside a river. 2. Amphiboly : change of meaning due to grammar (syntactical confusion) One morning, I shot an elephant in my pajamas. Thus, elephants wear pajamas.

3. Composition/Division: The confusion is in attributing the characteristics of part (or whole) to the whole (or part). All the books in this library are good. Thus, this is as a good library. (Composition) This is a good library. Thus, you can be sure that all the books in this library are good. (Division)

Class Discussion – Homework Assignment Be sure you understand the argument. What is the claim? What are the premises for the claim? Determine if the argument is deductive or inductive and apply the appropriate test either for validity or strong support. Identify and weed out any logical fallacies, rhetoric, subjectivity, or irrelevancies. Clarify any vagueness or ambiguity. Examine the truth of the premises. If the argument is inductive, evaluate the evidence.