Logic and Critical Thinking

CCC80012nd Term 2013

INTRODUCTION

Course Particulars

• Instructor: Dr. Michael Johnson• Office: Room HSH219, Ho Sin Hang Building• Office Hours: Mondays 15:00 to 16:00• Email: michael.dracula.johnson@gmail.com• Office Telephone: 2616 7052

Course Website

Go to

http://michaeljohnsonphilosophy.com/logic-and-critical-thinking-2013/

All of the powerpoint slides will be posted there, along with reading assignments and homework assignments.

Meeting Times

Monday 13:30 to 14:50 Leung Kau Kui (LKK) G01

Thursday 13:30 to 14:50LKK 107

Assessment

• Attendance: 10%.• Four homework assignments, each worth 5%

of the grade, for a total of 20%.• One in-class midterm on 11 March, worth

30%.• One cumulative final exam, worth 40%.

Attendance

Attendance is required and accounts for 10% of your final grade.

You cannot get an ‘A’ in this course if you do not attend classes.

Every day you don’t attend, you lose 0.5 points off your final grade, up to a maximum of 10.

Final Exam

The final exam will occur during the scheduled exam period (TBA).

It will consist of multiple choice and short-answer questions.

It is worth 40% of your final grade.

More details will be announced as the date of the final approaches. There will be a review (2/5).

Important Note

Students shall be aware of the University regulations about dishonest practice in course work and the possible consequences as stipulated in the Regulations Governing University Examinations.

What is Critical Thinking?

There are two basic decisions to make in life:

1. Decide what to believe: What do I believe?

2. Decide what to do: What do I do?

Deciding What to Believe

The things you believe (or disbelieve) are claims.

Examples of claims include:• Aliens exist.• 2 + 2 = 4.• Pocari Sweat is better than Aquarius.• You should kill children for fun.

Claims

Claims can be:

General or specificTrue or falsePlausible or implausibleReasonable or unreasonableSupported by evidence or not…

Example: Theories

Scientific theories are claims that are supported by lots of evidence, that integrate lots of our knowledge, and that explain and predict lots of phenomena.

Example: Guesses

Guesses are claims that the guesser only believes might be true, or are probably true.

Example: Lies

A lie is a claim that is known to be false and is made to deceive you into believing something false.

Claims

Scientific theories, guesses, and lies are all claims. There are lots of other types of claims: hypotheses, deductions, considerations…

A claim is something that is presented as true.

Sometimes good reasons are given for accepting it, sometimes no reasons are given, and sometimes misleading reasons are given.

Critical Thinking

Is there any evidence to support the claim?

Is the evidence reliable and trustworthy? How reliable is it? Should you accept it?

Does the evidence actually support the claim?

Is there other evidence you should consider?

Critical Thinking

Critical thinking involves asking these questions at the right times, knowing how to answer them, and knowing how to use those answers to accept or reject a claim.

This is a skills-oriented class. These are the skills we will learn.

You Already Do It

You are already a critical thinker. You use critical thinking skills all the time, even if you don’t know it.

Is there any evidence?

On a lot of airlines, you are required to turn off your cell phones and other electronic devices during takeoff and landing.

Claim: Keeping your devices on poses a danger.

But is there any evidence that this is true? Are there studies? What do scientists say?

Is there any evidence?

Flu season comes and it’s really bad. You should probably get a flu shot.

Or should you go to the traditional Chinese medicine shop? They say their medicine can prevent the flu too.

How reliable is the evidence?

Here’s a common story you’ll hear:

Claim: Oh, you have a cold? You should get the doctor to prescribe antibiotics for you.

Evidence: I got a cold and after a couple days was feeling really bad. I got some antibiotics and two days later, I felt great!

How reliable is the evidence?

But this can’t be true. Colds are caused by viruses, and antibiotics only work on bacteria.

The story you heard is a case of regression to the mean. People go to the doctor when they’re feeling worst. Of course they feel better later, they would feel better later anyway. Colds usually take care of themselves in 6 days.

Does the evidence support the claim?

Companies often pay celebrities and other public figures to endorse their products.

Claim: You should buy/ use this product.Evidence: Celebrity X buys/ uses this product.

But is it any reason to buy something that some other person is paid to say they like it?

Does the evidence support the claim?

But what do those doctors know about the health effects of cigarettes? Have they done studies?

Maybe they smoke Camels because they’re cheaper, or because they’re “cooler” or for some other reason.

Is there other evidence to consider?

Claim: Prayer heals the sick.Evidence: My mother had cancer, but then I prayed for her. Her cancer went into remission.

But how many people were prayed for and not cured? How many people were not prayed for, but still had their cancer go into remission? Does prayer work or was this just an accident?

Critical Thinking

Becoming a better critical thinker involves exercising these skills, asking these questions and finding out the answers, more often and more effectively and in a wider range of circumstances.

Logic

This course is called Logic and Critical Thinking, and we will be learning about logic.

Logic is a helpful tool for verifying the quality of arguments.

Philosophical Arguments

In ordinary English, an argument is where two or more people have different views, and they heatedly or angrily discuss them.

In philosophy, it’s when we present certain claims as evidence for other claims. So critical thinking is about evaluating arguments– are the claims presented as evidence true? Do they support the conclusions?

Validity

An important concept in logic is validity, a particularly strong sort of evidential support.

An argument is valid = if the claims presented as evidence in the argument (the “premises”) are true, then the claim that evidence supports (the “conclusion”) of the argument must be true (cannot be false).

Formally Valid Arguments

Ancient philosophers (both Western and Chinese) discovered that you can tell that some arguments are valid by looking at their form alone.

Example

Here’s an example of a valid argument form:Evidence: If A is true, then B is true.Evidence: A is true.Claim: Therefore, B is true.

Notice that even if you don’t know what the claims A and B are, you know that if the evidence is true, then the claim is true.

Logic

Logic is the study of formal validity. We try to find all the valid logical forms. That way, if we ever find an argument that has one of those forms, we will know for sure that it is valid.

It wasn’t until recently that we (or a German mathematician named Gottlob Frege) found a way to find all the valid logical forms. This is the logic we learn about today.

The Limits of Logic

Logic isn’t the entire story. It doesn’t have anything to say about the good arguments that are not formally valid, and it can’t identify bad arguments.

There’s also another kind of “goodness” for arguments: a sound argument is valid and its premises are true. But logic alone can’t tell us what’s true.

Deciding What to Do

But critical thinking does not end there. Notice that we still do not know what to do.

Should I turn off my cell phone on an airplane?Should I smoke Camels?Should I eat shark fin soup if I want to avoid cancer?What do I do?

Choices

A choice is a decision between two or more actions.

Sometimes choices lead to the outcomes we desire with certainty. Sometimes they only likely lead to the outcome we desire. Sometimes our choices are very unlikely to get us the outcome we desire.

Choices

Choices can be:

Important or unimportantEasy or difficultRational or irrationalSuccessful or unsuccessful…

Critical Thinking

What outcomes can my choice lead to?

Does the outcome of my decision depend on factors other than what I choose to do?

What is the likelihood that deciding to take a specific action will lead to a specific outcome?

Which outcomes do I most prefer?

What outcomes can my choice lead to?

Here’s an example from the United States:

A lot of religious conservatives in the U.S. campaign to make abortion illegal, and elect government officials who say they will try to make it illegal. (Important background: the U.S. Supreme Court ruled that laws against abortion are unconstitutional.)

What outcomes can my choice lead to?

http://www.youtube.com/watch?v=xJh6frpykQk

But if abortion is illegal, presumably women who get abortions will go to jail. So do the campaigners who want to make abortion illegal want these women in jail? In the video, we see a woman who’s quite confused as to what outcome her position leads to.

What do the outcomes depend on?

Sometimes, when we make a choice, the outcome depends not just on what we’ve chosen to do, but also on what others have chosen.

Suppose I have a scholarship that I can offer to exactly one student to come to my school. If they don’t accept it, I cannot offer it to anyone else…

What do the outcomes depend on?

If I offer it to the best student, she is most likely to decline it (she has other scholarships to other schools, she may decide to go somewhere else).

If I offer it to the worst student, she is most likely to accept it (she probably has no other scholarships and no other admittances). But I don’t want to give money to the worst student!

How likely is this choice to effect this outcome?

Sometimes the same action can result in different outcomes with different likelihoods.

If I decide to have unprotected sex, there is some probability that I will get AIDS, some probability I will get syphilis, some probability I will not contract any STI, etc. These facts clearly matter to my decision.

Which outcomes do I most prefer?

Taking different actions (making different decisions) can often lead to different outcomes.

But it’s not always obvious which outcomes to prefer. Obviously $50 is better than $10. But suppose it costs the same to keep someone in jail as to pay for a student to go to college. Do you let criminals out and educate more people?

Framing and the Flu

Suppose a new type of flu is spreading through China and experts predict it will move to Hong Kong soon. If nothing is done, it will kill 600.

The government is deciding which of two plans to implement. They come to the following rigorous, scientifically certain evaluations of the plans:

Version 1

• If Plan A is adopted, 200 people will be saved.• If Plan B is adopted, there is a 1-in-3 chance

that all 600 will be saved, and a 2-in-3 chance that no one will be saved.

Version 2

• If Plan A is adopted, 400 people will die.• If Plan B is adopted, there is a 1-in-3 chance

that no one will die, and a 2-in-3 chance that all 600 will die.

Which outcomes do I prefer?

Version 1 and Version 2 describe exactly the same plans.

Plan A in Version 1 = Plan A in Version 2.Plan B in Version 1 = Plan B in Version 2.

Yet 70% of people go with Plan A in Version 1, while only 41% choose Plan A in Version 2.

For Next Class

Go to the course website: http://michaeljohnsonphilosophy.com/logic-and-critical-thinking-2013/schedule-and-readings/

Read the reading for next time.