EVALUATION Part 2

Last Class Good, true, knowledge, belief, opinion Acceptability Evaluating claims Types of statements Unconvincing arguments Good premises and good reasoning Good premises and bad reasoning Bad premises and good reasoning Bad premises and bad reasoning

Today Two types of reasoning/arguments Deductive Non-Deductive Validity and Soundness Evaluating arguments

Deductive Arguments Premises guarantee the conclusion (100%) Example: All woman are mortal Kate is a woman Therefore, Kate is mortal. A matter of degree? Can be either valid or invalid

Validity An argument is valid if it is impossible for the conclusion to be false if all of the premises are true. Its about the form and structure and the relationship of support among the premises and conclusion. Invalid: T, T, F Example… The heart is in the chest and the chest is a part of the body. So the heart is a part of the body.

Validity Cont’d Question: Does a valid argument require that the premises be all true? Yes or no. Example… All winged animals can fly and pigs have wings, so pigs can fly.

Valid or Invalid: Exercises Recall: Deductive Args, 100% guarantee of Conclusion 1. All of Alex’s students are bored and you’re Alex’s student. So you are bored. 2. Some Athletes use PEDs and Steve is an athlete. So he uses PEDs. 3. Winters in Canada are cold and Montreal is Canada. Montreal has cold winters. 4. If the Red Sox win the AL East, then the Blue Jays won’t make it to the postseason. But the Red Sox didn’t win the AL East. So the Jays won’t make the postseason. 5. Laura is Donna’s daughter, so Donna is Laura’s mother.

Sound / unsound For our purposes as good logicians, an argument is sound if it is has a valid form and all true claims (P and C) Practice exercises… 1. Montreal is in Quebec and Quebec is part of Canada. So Montreal is a part of Canada. 2. Quebec is a francophone province and Quebec is part of Canada. So Canada is composed of at least one francophone province. What about this one The earth is flat. Flat things are biscuits. The earth is a biscuit.

How to check for validity We will learn formal strategies for determining an argument’s validity after the first midterm. Ask yourself? Is it possible for the premises to be true and the conclusion false? If yes, then it is invalid. Use your best strategies for evaluation.

Four Possibilities Valid: False premises and a false conclusion Valid: False premises and a true conclusion Valid and Sound: True premises and a true conclusion Invalid: True premises and a false conclusion

False premises and a false conclusion The moon is a made of refined sugar and refined sugar is a healthy food. The moon is a healthy food.

False premises and a true conclusion My dog is a chicken. Chickens don’t lay eggs. So my dog doesn’t lay eggs.

True premises and a true conclusion Pepsi is a soda and sodas are bad for your teeth. So Pepsi is bad for your teeth.

True premises and a false conclusion Sharks are apex predators. Many apex predators live on land. Sharks live on land.

On your own time… Try to come up with your own arguments that fit each of the possibilities we’ve discussed here today: Valid: False premises and a false conclusion Valid: False premises and a true conclusion Valid and Sound: True premises and a true conclusion Invalid: True premises and a false conclusion

Non-deductive Arguments The idea here is to make a convincing case of the likelihood of the conclusion. Probability; Matter of degree > 50% Can be either successful or unsuccessful

Examples For the following: (1) state whether it is successful or unsuccessful and (2) provide a brief explanation for why it is, or is not, successful. Kristina is a student a uOttawa and a recent, random survey of 1000 students on campus revealed that 75% of students think the University needs to build and new, bigger library complex. So Kristina probably thinks the University needs a new library.

Examples For the following: (1) state whether it is successful or unsuccessful and (2) provide a brief explanation for why it is, or is not, successful. 1)I’ve met sixteen major league pitchers and each of them have either had shoulder problems or needed shoulder surgery at least once in their career. Marvin wants to pitch in the majors, so, if he makes it, he’ll likely have troubles with his shoulder. 2) I’ve owned two HP computers, and both broke. I am convinced that all HP computers are garbage.

Examples For the following: (1) state whether it is successful or unsuccessful and (2) provide a brief explanation for why it is, or is not, successful. A recent poll by a national newspaper discovered that more than 65% of Canadians believe that a wall needs to be erected along the Canadian border with the United States. However, only half of those polled who were in favor of building the wall also agreed that the reason was the circus that is the current U.S. Election. Since my friend Emily is a Canadian, she probably thinks Canada needs to build a wall along the border with the U.S. because the current U.S. election is a circus.

Next Class Why the world does not exist! Exam Review Exam is one week from today