Critical Reasoning Important & Useful Tool

1. Critical ReasoningImportant & Useful Tool Why? Because we’re believers We are Hard-Wired Believers Our very existence depends upon belief You don’t get through a moment of your day without it On what are we grounding what we claim to know or believe? Does it stand up?

2. Arguments: a series of propositions (statements) put forward to support another proposition Propositions (Statements): a state of affairs that is either true or false Sentences: linguistic entities or vehicles used to express propositions Premises: propositions that off support for the conclusion of an argument Conclusions: the proposition that is inferred based on one or more other propositions in an argument Inferences: a proposition that is made (or inferred) based on one or more other propositions *can be either a premise or a conclusion

3. What do these have in common? No one was present when life first appeared on earth. Therefore, any statement about life’s origins should be considered as theory, not fact. Every law is an evil, for every law is an infraction of liberty. Since it turns out that all humans are descended from a small number of African ancestors in our recent evolutionary past, believing in profound differences between the races is as ridiculous as believing in a flat earth. The Food and Drug Administration should stop all cigarette sales. After all, cigarette smoking is the leading preventable cause of death. The reason we start a war is to fight a war, win a war, thereby causing no more war!

4. ArgumentsThe Bread & Butter The Ingredients • Propositions • Inferences

5. Propositions Proposition (Statement): an assertion that something is or is not the case (true or false) A sentence is neither true or false Proposition: the cat is on the mat • English: The cat is on the mat • Spanish: El gato está en la estera • French: Le chat est sur le tapis • Italian: Il gatto è sulla stuoia • Symbolic: ∃x (xC  xM)

6. Inferences • Inference: affirming one proposition on the basis of another (or others) • Conclusion: inference (All conclusions are inferences) • But not every inference is a conclusion

7. Inference 1. If I am a free creature than I must have free will. 2. Free creatures decide for themselves what they will do. 3. I am a free creature. 4. So I decide for myself what I will do. [inference, premise] C: Thus I must have free will. [inference, conclusion]

8. Premise(s) & Conclusion • Argument: consists of at least one premise and at most one conclusion • Premise: a reason for maintaining the conclusion, support for the conclusion • Conclusion: the inference made from the premise(s) • *Note: there can be more than one inference but only one conclusion

9. Conclusion Indicators • Therefore: for these reasons • Hence: it follows that • So: I conclude that • Accordingly: which shows that • In Consequence: which means that • Consequently: which entails that • Proves that: which implies that • As a result: which allows us to infer that • For this reason: which points to the conclusion that • Thus: we may infer

10. Premise Indicatorsusually (but not always) • Since: as indicated by • Because: the reason is that • For: for the reason that • As: may be inferred from • Follows from: may be derived from • As shown by: may be deduced from • Inasmuch as: in view of the fact that

11. No one was present when life first appeared on earth. Therefore, any statement about life’s origins should be considered as theory, not fact. • Premise: No one was present when life first appeared on earth. • Conclusion: Any statement about life’s origins should be considered as theory, not fact.

12. Every law is an evil, for every law is an infraction of liberty. • Premise: Every law is an infraction of liberty. • Conclusion: Every law is an evil.

13. Since it turns out that all humans are descended from a small number of African ancestors in our recent evolutionary past, believing in profound differences, between the races is as ridiculous as believing in a flat earth. • Premise: All humans are descended from a small number of African ancestors in our recent evolutionary past. • Conclusion: The belief in profound differences, between the races is as ridiculous as believing in a flat earth

14. The Food and Drug Administration should stop all cigarette sales. After all, cigarette smoking is the leading preventable cause of death. • Premise: Cigarette smoking is the leading preventable cause of death. • Conclusion: The Food and Drug Administration should stop all cigarette sales

15. The reason we start a war is to fight a war, win a war, therebycausing no more war! • Premise: We start a war in order to fight a war. • Premise: We fight a war in order to win a war. • Premise: As a result of winning a war, we end/stop war. • Conclusion: We start wars to end/stop wars.

16. Practice • A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed. (2nd Amendment of the Constitution) • Premise? • Conclusion?

17. Practice • Of all our passions and appetites the love of power is of the most imperious and unsociable nature, since the pride of one man requires the submission of the multitude. (Edward Gibbon, The Decline and Fall of the Roman Empire) • Premise? • Conclusion?

18. Practice • Sir Edmund Hillary is a hero not because he was the first to climb Mount Everest but because he never forgot the Sherpas who helped him achieve this impossible feat. He dedicated his life to helping build schools and hospitals for them. • Premise? • Conclusion?

19. Practice • He that loveth not knoweth not God; for God is love. (1 John 4.8) • Premise? • Conclusion?

20. Practice • Because light moves at a finite speed, looking at objects that are millions of miles away is actually looking at light that was emitted many years ago. • Premise? • Conclusion?

21. Every argument is a series of propositions but not every series of propositions is an argument.

22. Is there a Conclusion? Is it Clearly Stated? • Leonardo understood, described, and illustrated the principles of hydrodynamics, gross anatomy, physics and astronomy. He invented the helicopter, the armored tank, and the submarine. He painted like an angel and despite being phobic about deadlines wrote often and well. In addition, according to Vasari, he was drop-dead gorgeous. And he generated all this near-magical accomplishment from behind a curtain of personal discretion so dense and insulating that no historian or psychologist has been able to pull it aside to reveal the person behind the personage.

23. 1st Trick: recognizing when we’ve got an argument • 2nd Trick: determining whether it’s a good or bad one

24. Conditions for Good Reasoning The premises are believable (warranted, justified). Consider all relevant information. The premises provide good grounds for accepting the conclusion.

25. When Claims Conflict • Conflict: When a claim conflicts with other claims (including background beliefs) we have good reason to accept, we have good grounds for doubting it.

26. This is gin, I’m drinking right now.

27. Conflicting Claim: TBackground Beliefs: F

28. Background Beliefs vs. Worldviews

29. Evidence/Relevant Info. • We should proportion our belief to the evidence.

30. Expertise Relying on Expertise * If a claim conflicts with expert opinion, we have good reason to doubt it * When experts disagree, we have reason to doubt

31. Personal Experience • It’s reasonable to accept evidence provided by personal experience only if there’s no good reason to doubt it. 1. Impairment * Perception/Memory: Constructive

32. 2. Expectation

33. 3. Innumeracy

34. Resisting Contrary Evidence: Galileo’s crystal mountains & valleys Fallacy: Argument from Ignorance/Appeal to Ignorance

35. 5. Looking for Confirming Evidence

36. 6. Preferring Available Evidence