Read Chapter 4 of Epstein's Critical Thinking.

This chapter is divided into five sections.   We will discuss three of these sections only briefly, while we will spend more time on two of the sections. 

A.  The Need to Repair Arguments

In our normal daily conversations, we very seldom state all of the premises that are needed to make an argument valid or strong.   Often, our listener or reader will share our assumptions and background knowledge, and it is not necessary to state all of the premises.  Consider the following example.

We should put some gasoline in the car.  I noticed that the tank is almost empty.

This very simple argument that concludes, "We should put some gasoline in the car," relies on several unstated premises, such as, "The car will not operate without gasoline.  And we want the car to operate properly."

It would seem very strange to state assumptions that are so evident to most people.  

Yet sometimes, the unstated premise is not so obvious, or the unstated premise is clearly false.  In such cases, it is necessary to reveal the unstated premise to evaluate the argument.

We can say, then, that to repair an argument is to improve it by adding a premise or conclusion that is unstated in the original argument.  We will discuss further examples of repairing arguments later in this lesson.

B.  The Principle of Rational Discussion - The need to repair arguments arises from our everyday discourse in which arguments often are incomplete.  To repair a person's argument is to clarify what he or she means so that it can be evaluated. 

To repair a person's argument is to assume the following:

1. That the person knows about the subject under discussion.

2. That the person is able and willing to reason well.

3. That the person is not lying.

The first principle points out that effective critical thinking requires an individual to have knowledge about a variety of subjects, and to be willing to learn new things.   One textbook on critical thinking says that the most important need for good critical thinking is knowledge.  Criticial thinking skills in isolation from developing knowledge of a variety of subjects will not be very helpful.  Critical thinking provides rules about the way to think, but it will be impossible to apply those rules correctly and meaningfully if you do not know about the subject under discussion.   The need to have a breadth of knowledge is one of the reasons why colleges and universities require students to take a general education foundation for all degree programs.  The general education program (the University College Core Curriculum at FSU) is designed to give you that breadth of knowledge.

The second principle speaks to the ability and willingness to reason well.  I am convinced 100% that every human being has the ability to reason well.  Critical reasoning is a natural ability of all people, I believe, though some are better than others because they have practiced it more.  This course is designed to increase your practice.

While we all have the ability to think critically, all too often, however, we do not have the will to do so.  Critical thinking can be hard work.   Sometimes in life it is easier to follow one's emotions or to do what others expect than to reason about topics.

The third principles indicates that it is impossible to enter into a rational discussion with another person if that person is lying.

If a person does not meet any of the above principles, then you should probably not waste your time trying to repair the individual's arguments.

C. Relevance - This is an extremely important concept in repairing arguments.  If a person gives premises that are irrelevant to the conclusion, then we need not try to repair it.  What does "relevance" mean?  In evaluating an argument, we say that a premise is irrelevant if there is no apparent connection between the premise and the conclusion it supposedly supports; an irrelevant premise, as your book states it (p. 71), can be deleted and it doesn't weaken the argument. 

Consider the following argument:

Mr. Smith's proposal regarding taxes will be bad for economy.  The increased taxes will reduce consumer spending, which will lead to unemployment.  Besides, Mr. Smith's father was a card carrying member of the Socialist party.

The premise about increased taxes reducing consumer spending is evidently related to the conclusion and, if true, would provide a good reason to support the conclusion. 

It is difficult to see the connection between the premise about Mr. Smith's father and his proposals; It is difficult to imagine what premise would link the premise with the conclusion. (The only one I can think of would be something like: "No proposal from the son of a card-carrying member of the Socialist Party will be good,"  but this premise is obviously false.)  We can delete it without weakening the argument.    Another way of saying that a premise is irrelevant is to say that even if it's true, it gives us no good reason to accept the conclusion.

An argument with premises that are all irrelevant is beyond repair.

The person making the argument would need to show us how the premise is linked to the conclusion before we accepted it.

D. Implying and Inferring

In this chapter we are discussing the way we often present arguments in everyday conversation and discussion.  Often, we leave our conclusions unstated, because we assume they are obvious.  Often they are.  If a parent tells a child that his or her behavior was unacceptable, it should be obvious that the parent intends for the child not to repeat that behavior.

When you, as a speaker or writer, leave your conclusion unstated, then we can say that you are implying that conclusion.  When I, as a listener or reader, state what I believe your conclusion to be, then I am inferrring the conclusion. 

An implied conclusion, then, is an unstated conclusion.  If a speaker leaves a conclusion unstated, then he or she is implying that conclusion.  When the listener decides that an unstated claim is the conclusion, he or she is inferring it.

The difference between implying and inferring can lead to many miscommunications and misunderstandings.

Consider the following example:  I remind you that we are having an exam during the next class period, and then I tell you to be sure to bring your textbooks.  You infer from what I say that the test will be an open-book test, which means you will probably not study as much as you would otherwise.  When you come to class for the exam and I say put away your books, you are upset.  When you say that I told the class the test would be an open-book test, I deny this, to which you reply that I implied it.   I say that I didn't imply it, but that you inferred it, and that you inferred incorrectly, since I planned to begin the discussion of the next chapter after the test and that's why I asked you to bring your textbooks.

The lesson here is that it's probably wise to be careful about leaving your conclusions implied, since someone may misunderstand your conclusion.  At the same time, be careful to make sure that what you infer is what the other person meant.

Consider each of the following. What do you think the speaker is implying?

1. She:  We need to buy a new car.  He:  We can barely pay our bills now, and our current car is not so bad.

What has he implied?  What could she reasonably infer?

2. Father to son:  One of us needs to cut the grass and trim the hedges.  And I have to go to the office.

What has the father implied?  What should the son infer?

3. He:  So where should we go on vacation this year? Myrtle Beach or Mexico?   She:  We've never been to Mexico, though we've been to Myrtle Beach many times.

What has she implied?  What could he reasonably infer from her comments?

4.  Teacher to student:  You must either study very hard and do well on this next test, or withdraw from the class. Student:  I don't have the time to study for the next test.

What has the student implied?  What could the teacher reasonably infer?

5. Sales Manager to Sales Personnel:  Our sales have declined for the past four months.  If we don't see an imporvement this month the company will have no choice but to reduce its sales staff.

What has the Sales Manager implied? What could the sales personnel reasonably infer?

6. Student to Roommate:  When I left the room two hours ago, my Critical Thinking homework was on the desk and now it is gone.  You were the only person here during the past two hours.

What has the student implied?  What could the roommate reasonably infer?

7. Young man to girlfriend:  I'm sorry I was late for your party, but I had to wash my car, and then I got really interested in the Jerry Springer show.

8. Young woman to boyfriend:  I'm sorry that all could afford for your birthday present was a pocket knife.

9. Man speaking about a woman's argument about a political issue:  "That's pretty good.  For a woman."

What has the man implied?  What could the woman reasonably infer?

10.  Student to teacher:  "I'll do anything for an A."   Teacher:  "What are you doing tonight?"

What has the teacher implied?  What could the student reasonably infer?


With some of these, the implication and inference are reasonably clear.  In other, there is much more room for misunderstanding.

E. Repairing Arguments - Guidelines and Examples

Imagine a garage that says on the top of it "Jon's (or your name) Argument Repair Shop."  People come in at all time of the day with all sorts of arguments.   They know something is wrong with their arguments; they sense that something is missing, that their arguments are incomplete, but they don't know how to fix them.   As an "Argument Repair Specialist" you must try to fix their arguments.   How do you do this?

It is important here to remember the criteria for a good argument.  A good argument must be valid or strong, have true premises, and the premises must be more plausible than the conclusion.  We should keep these criteria in mind when repairing arguments.  If someone gives an argument that is incomplete, something is missing, then if we can make an argument that meets these criteria, then we can repair it.   Otherwise, we have to say it is unrepairable.

Consider the following example.

"This banana is not green.  So it must not be ripe."

This simple example shows that you must pay close attention to the words people use in their arguments, because these will give you a clue as to what they intend.  Two words that are especially important in this argument are "so" and "must." 

"So" is a conclusion indicatorUsually (and it is important to see that there are exceptions to this) "so" precedes a person's conclusion.  Other such conclusion indicators are "therefore," "hence," "thus," "consequently," "we can then derive," "it follows that." 

Other words, such as "since," "because," "for," "in as much as," "given that," "suppose that,"  "it follows from," usually (again note that it is not always the case) precedes a premise.  We call them premise indicators. 

"So " lets us know the person's conclusion. 

"Must" lets us know that the person intends for the conclusion to follow absolutely from the premise, that is, if the premise is true the conclusion must be true.  In other words, the speaker intends the argument to be valid.  To repair the argument, we must be able to supply a premise to make the argument valid.

If we say "All green bananas are not ripe," this makes the argument valid, for if it is true that All green bananas are not ripe, and that this banana is green, then it MUST be true that this banana is not ripe.   You have made the argument valid, but are the premises true?  As far as I know, green bananas are unripe, and so if the person is telling the truth about the banana being green, the argument is a good one.

Another example: 

Since you are not rich, you can't be smart.

The premise follows "since."  The conclusion is "you can't be smart." 

Note the use of "can't" in the conclusion.  The speaker evidently intends this as a valid argument.  What do you need to add to make this a valid argument?  It would have to be "All smart people are rich." 

(If you were tempted to add the premise, "All rich people are smart," please note why that will not make the argument valid.  To say "All rich people are smart" still leaves open the possibility that some smart people are poor.  And, hence, the two premises could be true, "All rich people are smart.  You are not rich," and the conlusion, "You are not rich" still be false.)

Our repaired argument is:  "All smart people are rich.  You are not rich.  So, you can't be smart."

We have repaired the argument to make it valid.  But, what about the premise we have added?  Is it true that all smart people are rich?  Obviously not.   Many of us know people who are smart, but not rich. 

If an argument is intended as a valid argument, but the only premise we can give to make it valid is false, then the argument is unrepairable.

These are very simple examples.  Let me give you one from real life.  Just the other day, on a radio show, the question listeners were asked to respond to was, "Should Pete Rose be allowed to be inducted into the Baseball Hall of Fame."  

(For those of you who may not know, Pete Rose was a great baseball player for the Cinncinnati Reds, who was convicted of gambling and as a result banned from baseball.   There is no question that he was a truly great player deserving of election to the Hall of Fame, but unless his ban is lifted, he cannot be inducted into it.)

One caller responded to the question with something like this. "Yes, I think that Pete Rose should be inducted into the Hall of Fame, because after all, President Clinton lied under oath and is still sitting in the White House.  If he can get by with that, then the ban on Pete Rose should be lifted."

At first, one might be tempted to question the relevance of the comment about the president.  But there is an argument here, though much (much!) has been left unspoken.  Can we repair it?  Can we add the missing premises to make it a good argument?

The person's argument rests on an analogy between Pete Rose's gambling and the President's legal troubles.  How can we articulate this in a premise? Perhaps something like, "If the president was unpunished for a crime, then Pete Rose should be forgiven for his crime."  Note that if this premise is true, then the argument is valid.  But, what about the truth of the premise?  There are many problems here.  First, the president underwent impeachment hearings, but was not removed from office.  Pete Rose was tried and found guilty of his offenses.   This difference makes comparions difficult.  Second, if we say the President should have been punished but was not, does that mean that no-one should ever be punished?

We have to say that this argument is unrepairable.  The individual needs to develop it a little more fully.  Please note, however, that just because we say the argument is unrepairable, we are NOT saying the conclusion is false.  We are simply saying that the argument as presented does not give good reason to accept the conclusion.

Can the following two arguments be repaired?  If so, show what must be added to repair them. If not, why not?

Meet Ralph

Ralph barks. 

Ralph must not be a cat.

Can you repair this argument?

What is the missing premise?  Is it true?

All students who come to class regularly are liked by their teachers.

Camille is liked by her teachers.

Can you repair this argument?