Logic and
Critical Thinking

Philosophy 4

Gale Justin

The objective of today’s class is to learn how:

To evaluate the strength of an argument

Evaluating an Argument:

An argument offers reasons to believe that some statement is true.

When you evaluate an argument, you are trying to decide whether someone should be persuaded of the truth of the conclusion on the basis of the reasons being offered. That is, you are deciding whether the reasons being given show or do not show that the conclusion is true. And you must state a reason to support your decision on the issue.

Consider the following argument:

uCapital punishment is justified in this one case: against terrorism in the form of hostage taking. Jailing convicted terrorists only incites co-conspirators to take further hostages to bargain for a jailed terrorist’s release. If death is the only penalty for terrorism in the form of hostage taking, further escalation of that problem will stop.

To evaluate this argument,

uYou should not focus on the question of whether or not the conclusion is true or false. This is because the conclusion could be true even if the reasons being given in the argument do not show that the conclusion is true.

uAlso you should not focus on whether you are for or against the death penalty.

uRather you should focus on the question of whether there are any objections that can be raised about the reason being given for the conclusion.

To put the point in a slightly different way:

To criticize an argument, you need first to identify the reason that the author is offering for the conclusion and then give your own reason why the author’s reason is not as strong as it would need to be for the argument to be entirely persuasive.

Consider the reasons given to persuade you of the fact that capital punishment should be used on terrorists and hostage takers:

P1: Jailing a terrorist will incite the co-conspirators to take more hostages.

P2: Putting the terrorist to death will stop the hostage taking.

Can objections be raised to either or both of these reasons?

With respect to the just mentioned argument, one might criticize it as follows:

Neither of the reasons given for the conclusion that terrorists who take hostages ought to get the death penalty are good reasons. There is no clear evidence to support the first premiss: that jailing a terrorist is actually a cause of terrorist activity.

The second premiss seems to be false, since Israel has adopted the policy of killing terrorists and it experiences continued terrorist attacks.

Here is another argument:

Students ought to decide on the requirements of a college curriculum because they are paying for the courses that they take.

Consider the reason being given for the conclusion that students should decide college course requirements.

P1: Students are paying for the courses that they take.

What assumption is being made about the connection between “paying for something” and “having a choice about the product.”

Are there any problems with this assumption?

With respect to the argument about student choice, one might criticize it as follows:

The reason given to support the conclusion assumes that if you pay for something, you should have the right to choose the product that you are paying for. In very general terms this is correct. A person has a right to spend his/her money as he/she sees fit. But in specific cases the assumption is flawed. Deciding to spend money on a doctor does not give a patient the right to make decisions about treatment.

To criticize an argument, you must:

uIdentify the conclusion of the argument.

uIdentify the reasons given for the conclusion (i.e. the premisses of the argument).

uState a reason (or reasons) why the reason supporting the conclusion is not a strong reason.

It is very important to remember that:

In criticizing an argument you are not arguing that the conclusion is false. You are simply showing that the reason given for the conclusion is not a strong reason.

To criticize an argument you need not believe that the conclusion is false. In fact, you should adopt an impartial attitude towards the conclusion and focus on how much evidential weight the reason provides the conclusion.

When you evaluate an argument, you can make two kinds of criticisms of the argument.

uThe content of the premisses of the argument can be criticized. This kind of evaluation is called a content criticism.

uThe relationship between the premisses and the conclusion can be criticized. This kind of criticism is called a formal criticism.

To make a content criticism:

uYou give some reason for thinking that one or more of the premisses of the argument is false.

uFor example, “The oldest rule in my rule book, which is rule number 41, states that anyone over 5 feet tall should leave the courtroom immediately. You Alice, are over 5 feet tall. Therefore, the oldest rule in my rule book implies that you (Alice) should leave the courtroom immediately.” What reason is there for thinking that one of the premisses of this argument is false?

To make a formal criticism:

uYou give some reason for thinking that the relationship between the premisses and the conclusion does not show that the conclusion is true.

uThe premiss-conclusion relationship can be criticized for the following reasons.

Reasons for making a formal criticism:

uThe cases mentioned in the premisses are relevantly different from the case mentioned in the conclusion.

uThe cases mentioned in the premisses are about the past and the conclusion is about the future.

uThe case mentioned in the premiss is a single case (or an unusual case) the conclusion is about the majority (or all) cases (or usual cases).

Examples:

uWe do not allow the sale of drugs on campus. So we should not allow the sale of soft drinks on campus.

uWe have never had a female president. So it is unlikely that we will ever have a female president.

uGrant was an alcoholic and a great general. So any general who is an alcoholic is a great general.