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What makes a Good Argument?

What makes a Good Argument?. Two Characteristics of Good Arguments. 1. The premises are true 2. The argument has proper form. True Premises. The premises are true when what they say about the world is accurate. Proper Form.

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What makes a Good Argument?

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  1. What makes a Good Argument?

  2. Two Characteristics of Good Arguments • 1. The premises are true • 2. The argument has proper form

  3. True Premises • The premises are true when what they say about the world is accurate

  4. Proper Form There is a relationship or connection between the premises and conclusion that make you believe the conclusion is true

  5. Deductive Argument You go from a general principle to a specific example It gives necessity

  6. All men are mortal • Socrates is a man Therefore (3) Socrates is mortal

  7. If all the members of the class of things called MEN have a particular characteristic called MORTALITY And Socrates is a member of that class called MEN Then Socrates MUST have that characteristic called MORTALITY

  8. Why? Because we have established a necessary / logical connection between the premises and the conclusion Such that if the premises are true then the conclusion must be true

  9. Examples • All men are mortal (1) All A has B • Socrates is a man (2) C is A There: Therefore (3) Socrates is mortal (3) C has B

  10. Valid Deductive Argument • The conclusion follows necessarily from the premises

  11. Example • All men have brown hair • Socrates is a man Therefore (3) Socrates has brown hair Is this Valid? YES!

  12. Proper Form Test Book says that if we assume the premises are true This will help us determine if the argument passes the proper form test This true only for Valid Deductive Arguments Not true for Sound Deductive Argument

  13. Sound Deductive Argument • Valid argument with true premises

  14. All roses are plants (1) All A’s are B’s • All roses have thorns (2) All A’s are C’s Therefore Therefore (3) All plants have thorns (3) All B’s are C’s

  15. Improper Form If all the members of the class of things called ROSES have the characteristic of being PLANTS And if all the members of the class of things called ROSES have the characteristic of having THORNS Then is it necessary that all plants have thorns?

  16. No! Why? Because the premises only establish a necessary connection between Roses and Plants Roses and Thorns But not between Plants and Thorns

  17. Proper Form Must establish a necessary connection between the premises and the conclusion

  18. Exercises 2.1 • Break up into groups • A 1-10

  19. 2.1A #1 • Oxygen is an element essential for life on Earth as we know it, Therefore, (2) If oxygen were to vanish from the Earth’s atmosphere, life as we know it would cease.

  20. 2.1A #1 I. Passes both tests.

  21. 2.1A #2 • All birds can fly. • Penguins are birds. Therefore, (3) Penguins can fly.

  22. 2.1A #2 Premise 1 is false, so argument does not pass TP test. If both premises were true, the conclusion would follow, so the argument does pass the PF test. It’s a valid argument.

  23. 2.1A #3 • All cars are blue. • All pigs have wings. Therefore, (3) All buses have three wheels.

  24. 2.1A #3 Fails both tests. Premises are false and irrelevant to conclusion.

  25. 2.1A #4 • Elephants are mammals. • Dogs are mammals. Therefore, (3) Elephants are dogs.

  26. 2.1A #4 Passes TP test This is an invalid deductive argument so it fails the PF test.

  27. Elephants are mammals. (1) E = M • Dogs are mammals. (2) D = M Therefore, (3) Elephants are dogs. (3) E = D

  28. 2.1A #5 (l) Many types of plastic can be recycled. (2) Many types of glass can be recycled. Therefore, (3) Many types of paper can be recycled.

  29. 2.1A #5 Argument passes TP test because both premises are true. But it does not pass the PF Inductive argument because of “many” not “all”

  30. 2.1A #6 • Julia Roberts is either a man or a woman. • Julia Roberts is a man. Therefore (3) Julia Roberts isn’t a woman.

  31. 2.1A #6 Fails the TP test because premise 2 is false. Passes the PF Test Disjunctive syllogism

  32. 2.1A #7 • Everyone likes pizza. • Everyone who likes pizza buys it regularly. Therefore, (3) Pizza sales will rise over the next six months

  33. 2.1A #7 Don’t know about TP (empirical question) Fails PF because if everyone was already buying pizza regularly. Why should sales increase? Wouldn’t they stay the same?

  34. 2.1A #8 (1) If you drop wood into water, it floats unless it’s held underwater by a heavy object. (2)Trees are made of wood. Therefore, (3) When trees fall into water, they float unless they’re held underwater by a heavy object.

  35. 2.1A #8 Passes both tests.

  36. 2.1A #9 • The discovery of antibiotics increased life expectancy. • Antibiotics have no effect on viruses, Therefore, (3) There must be some causes of reduced life expectancy besides viruses.

  37. 2.1A #9 The argument passes the TP test, but the argument does not pass PF test, as stated. Hidden Premises? (viruses reduce life expectancy)

  38. 2.1A #10 • All cars have three wheels. • Everything with three wheels is blue Therefore, (3) All cars are blue.

  39. 2.1A #10 The argument fails the TP test because both premises are false. IF they were true, they would prove the conclusion, so this argument passes the PF test. It is a valid (unsound) deductive argument.

  40. Audience • The audience of the argument is the group that the person making the argument wants to convince

  41. Exercises 2.2 • Do as class

  42. The Problem of Ignorance • The problem of ignorance is that we don’t know everything

  43. Proper Form • If the premises were true, they would provide support for the conclusion • It expresses a relationship between the premises and the conclusion

  44. Logical Relationships • In proper form arguments • We are looking for logical relationships • Based upon the premises • What can we determine about the conclusion?

  45. All men are mortal • Socrates is a man Therefore (3) Socrates is mortal (TP and PF: Sound) Relationship: If all members of the class of men have a certain characteristic: mortality Then all the members of that class MUST also have that characteristic: mortality

  46. Valid, but not Sound • All men have brown hair • Socrates is a man Therefore (3) Socrates has brown hair (FP and PF: Valid) Conclusion follows necessarily from the premises, but premises are NOT TRUE

  47. Groups (Fails PT Test) • All G1 are G2 (1) All roses are plants • All G1 are G3 (2) All rose have thorns Therefore (3) All G2 are G3 Therefore (3) All plants have thorns

  48. Exercise 2.4 • Break up into groups • A1-5

  49. 2.4A #1 • All dogs are mammals • All mammals are things with hair Therefore, (3) All dogs are things with hair Form B

  50. 2.4A #2 • If that’s a car, then I’m a donkey. (2) I’m a donkey. Therefore, (3) That’s a car. Form D Invalid Modus Ponens

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