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# Tutorial deductive and inductive arguments

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### Tutorial deductive and inductive arguments

1. 1. Deductive and Inductive Arguments In this tutorial you will learn to distinguish deductive arguments from inductive arguments.
2. 2. Tess : Are there any good Italian restaurants in town? Don : Yeah, Luigi's is pretty good. I've had their Neapolitan rigatoni, their lasagne col pesto, and their mushroom ravioli. I don't think you can go wrong with any of their pasta dishes. Based on what you've learned in Chapter 3, is this argument deductive or inductive? How can you tell?
3. 3. Tess : Are there any good Italian restaurants in town? Don : Yeah, Luigi's is pretty good. I've had their Neapolitan rigatoni, their lasagne col pesto, and their mushroom ravioli. I don't think you can go wrong with any of their pasta dishes. Inductive. The argument is an inductive generalization, which is a common pattern of inductive reasoning. Also, the conclusion does not follow with strict necessity from the premises.
4. 4. I wonder if I have enough cash to buy my psychology textbook as well as my biology and history textbooks. Let's see, I have \$200. My biology textbook costs \$65 and my history textbook costs \$52. My psychology textbook costs \$60. With taxes, that should come to about \$190. Yep, I have enough. Is this argument deductive or inductive? How can you tell?
5. 5. I wonder if I have enough cash to buy my psychology textbook as well as my biology and history textbooks. Let's see, I have \$200. My biology textbook costs \$65 and my history textbook costs \$52. My psychology textbook costs \$60. With taxes, that should come to about \$190. Yep, I have enough. <ul><li>Deductive. </li></ul><ul><li>This argument is an argument based on mathematics, </li></ul><ul><li>which is a common pattern of deductive reasoning. Plus, </li></ul><ul><li>the conclusion follows necessarily from the premises. </li></ul>
6. 6. Mother : Don't give Billy that brownie. It contains walnuts, and I think Billy is allergic to walnuts. Last week he ate some oatmeal cookies with walnuts, and he broke out in a severe rash. Father : Billy isn't allergic to walnuts. Don't you remember he ate some walnut fudge ice cream at Melissa's birthday party last spring? He didn't have any allergic reaction then. <ul><li>Is the father's argument deductive or inductive? How can </li></ul><ul><li>you tell? </li></ul>
7. 7. Mother : Don't give Billy that brownie. It contains walnuts, and I think Billy is allergic to walnuts. Last week he ate some oatmeal cookies with walnuts, and he broke out in a severe rash. Father : Billy isn't allergic to walnuts. Don't you remember he ate some walnut fudge ice cream at Melissa's birthday party last spring? He didn't have any allergic reaction then. <ul><li>Inductive. </li></ul><ul><li>The father's argument is a causal argument, which is a </li></ul><ul><li>common pattern of inductive reasoning. Also, the </li></ul><ul><li>conclusion does not follow necessarily from the </li></ul><ul><li>premises. (Billy might have developed an allergic reaction </li></ul><ul><li>to walnuts since last spring.) </li></ul>
8. 8. John is an agnostic. It necessarily follows that he doesn't believe in God. <ul><li>Is this argument deductive or inductive? How can you tell? </li></ul>
9. 9. John is an agnostic. It necessarily follows that he doesn't believe in God. <ul><li>Deductive. </li></ul><ul><li>This argument is an argument by definition, which is a </li></ul><ul><li>common pattern of deductive inference. Also, the phrase </li></ul><ul><li>&quot;it necessarily follows that&quot; is a deduction indicator </li></ul><ul><li>phrase. Also, the conclusion follows from the premises. </li></ul>
10. 10. Larry : Do you think Representative Porkmeister will be re-elected? Norman : I doubt it. Porkmeister's district has become more conservative in recent years. Porkmeister is a liberal Democrat, and 63% of the registered voters in his district are now Republicans. <ul><li>Is this argument deductive or inductive? How can you tell? </li></ul>
11. 11. Larry : Do you think Representative Porkmeister will be re-elected? Norman : I doubt it. Porkmeister's district has become more conservative in recent years. Porkmeister is a liberal Democrat, and 63% of the registered voters in his district are now Republicans. <ul><li>Inductive. </li></ul><ul><li>This argument is both a statistical argument and a </li></ul><ul><li>predictive argument, which are two common patterns of </li></ul><ul><li>inductive reasoning. Also, the conclusion does not follow </li></ul><ul><li>necessarily from the premises. </li></ul>
12. 12. If Buster walked to the game, then he didn't drive to the game. Buster didn't drive to the game. Therefore, Buster walked to the game. Is this argument deductive or inductive? How can you tell?
13. 13. If Buster walked to the game, then he didn't drive to the game. Buster didn't drive to the game. Therefore, Buster walked to the game. <ul><li>[This is the end of the tutorial] </li></ul>X Deductive. This argument is a hypothetical syllogism, which is a common pattern of deductive reasoning. Note, however, that the conclusion does not follow logically from the premises. (Maybe Buster rode his bike to the game, for example.) The argument commits the fallacy of &quot;affirming the consequent.&quot;
14. 14. Causal, Generalisation or Analogy? <ul><li>“ Introducing thick, fuzzy wool mittens for your immune system. Shield yourself…during the cold season and throughout the year. (Advertisement for throat lozenges) </li></ul>
15. 15. Causal, Generalisation or Analogy? <ul><li>“ I switched from European cars to American cars in 2000 and I had to endure two poor cars. Next time, I’ll give a Japanese car a try.” </li></ul>
16. 16. Causal, Generalisation or Analogy? <ul><li>“ I checked out the air pressure in the tires and even had the tires balanced and aligned. Yet the front end shimmy remains. One of the my tires must be out of round.” </li></ul>
17. 17. Causal, Generalisation or Analogy? <ul><li>I read with dismay your article about the use of pesticides in Third World countries. This is another example that makes plain the need to monitor and regular the activities of the business community, which has shown once again that profits are more important than the well-being of the planet. </li></ul>
18. 18. Causal, Generalisation or Analogy? <ul><li>Diadoras: They’re like Ferraris for your feet. Like the famous racing car, Diadora shoes are very quick, precisely engineered, responsive and good to look at…If you are as serious about winning as I am, to take a lesser shoe on court would be like driving the family sedan at LeMans. </li></ul>
19. 19. Causal, Generalisation or Analogy? <ul><li>How typical of Americans! They cannot appreciate any exquisite foreign food without vulgarizing and prostituting it. Look what has happened to pizza, to crepes and to Chinese and Japanese food – and now it’s happening to French delight, le croissant . Instead of elevating their taste to the food, they debase the food to their taste! </li></ul>