L2. Logic and Reasoning

Transcription

1 L2. Logic and Reasoning Alice E. Fischer September 4, 2018 L2. Logic and Reasoning... 1/23

2 Critical Thinking Valid Reasoning Bad Arguments Case Studies The Harvard Dean The Birther Community L2. Logic and Reasoning... 2/23

3 Valid Reasoning Critical Thinking Definition Valid Reasoning Common Errors in Reasoning Case Study: The Harvard Dean L2. Logic and Reasoning... 3/23

4 Valid Reasoning Definition Critical thinking is the process of evaluating a claim for the purpose of deciding whether to accept, reject, or suspend judgment about it 1. It involves both the ability and the desire to ask the right questions 2. It also requires us to use valid logical principles to assess the arguments and evidence presented. 1 1T.E.Damer in Attacking Faulty Reasoning. 2 Browne and Keeley, Asking the right questions: A guide to critical thinking L2. Logic and Reasoning... 4/23

5 Valid Reasoning A Good Argument It has been said that a proof is an argument that convinces another mathematician. What makes an argument convincing? All of the premises are true and you believe that they are true. Each premise is relevant to the issue. The collection of premises is sufficient; nothing important is missing. Valid steps of reasoning lead from the premises to the conclusion. L2. Logic and Reasoning... 5/23

6 Valid Reasoning Questions to Ask Yourself When you read an article, whether it is political or technical, think: What are the issues and the conclusions? What reasons and evidence are given? Is the evidence valid? What significant information is omitted? Is there ambiguity in the statement of the issue? Are there rival explanations and conclusions 3? Are there errors in reasoning? Do the writer s values distort his logic? 3 Occam s razor: The simplest explanation tends to be the right one. L2. Logic and Reasoning... 6/23

7 Bad Arguments An Error from Ambiguity Argument: My Mac CPU runs at a clock speed of 3.4 GHz. Your Intel CPU runs at 2.6GHz So my Mac will run Java faster than your Mac Mini. Fallacy: L2. Logic and Reasoning... 7/23

8 Bad Arguments An Error from Ambiguity Argument: My Mac CPU runs at a clock speed of 3.4 GHz. Your Intel CPU runs at 2.6GHz So my Mac will run Java faster than your Mac Mini. Fallacy: The words speed and fast are not measuring the same thing in the conclusion as in the premises. There is no direct connection between clock speed of the CPU and the speed at which a program executes. Many factors are involved in determining execution speed, including the architecture of the CPU, the number of cores, the memory speed, and the nature of the operating system. L2. Logic and Reasoning... 7/23

9 Bad Arguments Unwarranted Assumptions Argument: We tested this new software application for two weeks and in many ways. The testing did not reveal any remaining bugs. Therefore, there are no bugs in this software. Fallacy: L2. Logic and Reasoning... 8/23

10 Bad Arguments Unwarranted Assumptions Argument: We tested this new software application for two weeks and in many ways. The testing did not reveal any remaining bugs. Therefore, there are no bugs in this software. Fallacy: Not true. The absence of evidence of an error does not mean that no errors exist. L2. Logic and Reasoning... 8/23

11 Bad Arguments Missing Data Argument: The warplanes returned with gunshot damage to much of the body and tail, but none on the engines or cockpit. We should add armor to the worst-hit areas, but do not need to worry about the engines and cockpit. They must just be hard to hit. Fallacy: L2. Logic and Reasoning... 9/23

12 Bad Arguments Missing Data Argument: The warplanes returned with gunshot damage to much of the body and tail, but none on the engines or cockpit. We should add armor to the worst-hit areas, but do not need to worry about the engines and cockpit. They must just be hard to hit. Fallacy: Planes hit in the engines and/or cockpit went down and did not return. We should armor those areas. L2. Logic and Reasoning... 9/23

13 Bad Arguments Missing Data Argument: John is an excellent programmer. Rani is an excellent programmer. Chi-Fu is an excellent programmer. John, Rani, and Chi-Fu will make an excellent programming team. L2. Logic and Reasoning... 10/23

14 Bad Arguments Missing Data Argument: John is an excellent programmer. Rani is an excellent programmer. Chi-Fu is an excellent programmer. John, Rani, and Chi-Fu will make an excellent programming team. Fallacy: It is a large jump of faith to say that three good programmers will make a good team. Does one of these people have team-leadership skills? Are the others able and willing to take a follower role? Do all three work well in a group? Do their skills and knowledge complement each other? L2. Logic and Reasoning... 10/23

15 Bad Arguments Causation Argument: Tesla s Model 3 production is over a year behind schedule. The company had problems with the batteries. When they solve the battery problem, production will get back on schedule. Fallacy: L2. Logic and Reasoning... 11/23

16 Bad Arguments Causation Argument: Tesla s Model 3 production is over a year behind schedule. The company had problems with the batteries. When they solve the battery problem, production will get back on schedule. Fallacy: The delay was actually caused by highly complex manufacturing robots that could not quite do their jobs properly. The machines have now been replaced by hundreds of workers and production is beginning again. L2. Logic and Reasoning... 11/23

17 Bad Arguments Red Herrings Does the argument wander and distract you with irrelevant facts? John did not turn in the term project. He is a gifted young man. He is one of the kindest people I know. Last summer, he volunteered at a clinic in Guatemala. The flu has been going around school. I should not give him a failing grade. Fallacy: L2. Logic and Reasoning... 12/23

18 Bad Arguments Red Herrings Does the argument wander and distract you with irrelevant facts? John did not turn in the term project. He is a gifted young man. He is one of the kindest people I know. Last summer, he volunteered at a clinic in Guatemala. The flu has been going around school. I should not give him a failing grade. Fallacy: Is there a relevant good reason why the term project is not in? Would another week help? If not, this is a failing performance. L2. Logic and Reasoning... 12/23

19 Bad Arguments An Appeal to Belief Argument: A phone report said there is a hostage situation at this 81 Baker St. Our SWAT team is here to end the situation and arrest the guilty party. This man will not let us in the door and is getting physical. He must be holding the woman hostage. Save her! Shoot him. Fallacy: L2. Logic and Reasoning... 13/23

20 Bad Arguments An Appeal to Belief Argument: A phone report said there is a hostage situation at this 81 Baker St. Our SWAT team is here to end the situation and arrest the guilty party. This man will not let us in the door and is getting physical. He must be holding the woman hostage. Save her! Shoot him. Fallacy: That SWAT team killed an innocent man. An online gamer phoned in a fraudulent report because the dead guy was getting too close to #1 standing in the game. L2. Logic and Reasoning... 13/23

21 Bad Arguments Appeal to Emotion or Loyalty Argument: You are Hispanic and your car was totaled by an unlicensed driver. The attorneys in our law firm are Hispanic. Hispanics should stick together. Therefore, you should hire us to handle your case. Fallacy: Belonging to the same group or club is not a sufficient qualification here. The track record of the Hispanic law firm is much more relevant, but is not supplied. L2. Logic and Reasoning... 14/23

22 Bad Arguments Appeal to Emotion: e-mobs (group-think) July 2, 2018: As mob lynchings fueled by WhatsApp messages sweep India, authorities struggle to combat fake news. Five people were killed by a mob in India on Sunday after rumors spread on social media that they were child traffickers. The fake social media messages have left officials stunned and grappling with ways to control the rising violence. More than a dozen people have been killed across India since May in violence fueled mainly by messages on the WhatsApp service. The cases largely feature villagers, some of whom may be using smartphones for the first time. Inflamed by fake warnings of child trafficking rings or organ harvesters, they have attacked innocent bystanders and beaten them to death. L2. Logic and Reasoning... 15/23

23 The Harvard Dean Case Studies The Harvard Dean of Divinity The Birther Community L2. Logic and Reasoning... 16/23

24 The Harvard Dean The Harvard Dean of Divinity The Dean had a home office with a computer on which he stored thousands porn images. The Dean asked the Divinity School s computer technician to service his machine. The technician discovered the images. They were tasteless but not explicitly illegal. The technician reported the images to his boss, who reported to the administration. The Dean was asked to resign his leadership position but remained at Harvard as a tenured faculty member. Privacy is a right guaranteed by our constitution. So was the technician right or wrong to report the images? L2. Logic and Reasoning... 17/23

25 The Harvard Dean About the Dean and the Computer What data is missing? L2. Logic and Reasoning... 18/23

26 The Harvard Dean About the Dean and the Computer What data is missing? Who owned the home and the computer? Harvard. Harvard policy restricts the use of university computers to job-related purposes. L2. Logic and Reasoning... 18/23

27 The Harvard Dean About the Dean and the Computer What data is missing? Who owned the home and the computer? Harvard. Harvard policy restricts the use of university computers to job-related purposes. The Harvard Divinity School handbook explicitly prohibits storing inappropriate, obscene, bigoted, or abusive material. By law, an employee has no right to privacy when using a machine owned by his employer. L2. Logic and Reasoning... 18/23

28 The Harvard Dean About the Technician and the Visit Every employee has a responsibility to his or her employer. The technician was called because of a disk problem: Out of space to store files. The Dean asked for a new, larger, faster disk. L2. Logic and Reasoning... 19/23

29 The Harvard Dean About the Technician and the Visit Every employee has a responsibility to his or her employer. The technician was called because of a disk problem: Out of space to store files. The Dean asked for a new, larger, faster disk. The existence of the porn files was discovered in the normal course of doing the upgrade. L2. Logic and Reasoning... 19/23

30 The Harvard Dean About the Technician and the Visit Every employee has a responsibility to his or her employer. The technician was called because of a disk problem: Out of space to store files. The Dean asked for a new, larger, faster disk. The existence of the porn files was discovered in the normal course of doing the upgrade. The technician s supervisor asked him why it was taking so long to upgrade the Dean s disk. L2. Logic and Reasoning... 19/23

31 The Harvard Dean Your Conclusion? Now that you have more evidence: Did the technician behave ethically? Why or why not? L2. Logic and Reasoning... 20/23

32 The Birther Community Barack Obama s Birthplace: Authorities Spoke From 2008 to 2016, a number of conspiracy theories falsely asserted Obama was ineligible to be President of the United States because he was not a natural-born citizen Dec. 2009, Palin: I think the public rightfully is still making it an issue. April 7, 2011, Trump: [I am] not satisfied that Obama had proved his citizenship. 2012, Breitbart.com misidentified Obama s birthplace and stated that Obama was born in Kenya and raised in Indonesia and Hawaii. L2. Logic and Reasoning... 21/23

33 The Birther Community Obama s Birthplace: Wearing Blinders The actual facts were plain to see. 2008: The official Hawaiian birth certificate was released and confirmed by the Hawaii Dept of Health. April 2011: A certified version of the long form of the certificate was released. But the conspiracy theories flourished anyway: 2008 document: It was asserted that the certificate had been digitally forged with Adobe Photoshop and lacked a stamped seal of the state. L2. Logic and Reasoning... 22/23

34 The Birther Community Obama s Birthplace: Missing Data Many people misunderstood the constitutional requirements for eligibility and other simple facts. For them, there was missing information. Only one parent has to be a U.S. citizen for citizenship to carry over to a child. Living for a while in another country does not cause one to lose U.S. citizenship. Hawaii is one of our 50 states, not a foreign country. Birth certificates are not normally notarized. L2. Logic and Reasoning... 23/23

35 The Birther Community Appeal to Emotion and GroupThink; No Razor Here Conspiracy is never the simplest explanation, and Occam s razor tells us to reject it. In this case, the truth was inconvenient to many people. They simply did not like the truth, so they invented conspiracy theories that justified their anger and hatred. This faulty belief was strengthened by countless social media posts and conservative talk shows. A Harris Poll of adult Americans, March 2010: 25% of the respondents said they believed that Obama was not born in the United States. L2. Logic and Reasoning... 24/23