CHAPTER 9

CONSTRUCTING ARGUMENTS

CONSTRUCTING ARGUMENTS

• When we offer reasons to support a conclusions we are considered to be presenting an arguments.

• Argument: A form of thinking in which certain statements (reasons) are offered in support of another statement (a conclusion).

• Reasons: Statements that support another statement (known as a conclusion) justify it or make it more probable.

• Conclusion: A statements that explain, asserts or predicts on the basis of statements (known as reasons) that are offered as evidence for it.

Cue words for arguments

• Our language provides guidance in our efforts to identify reasons and conclusions.

• Certain keywords known as cue word, signal that a reason is being offered in support of a conclusion or that a conclusion is being announced on the basis of certain reasons.

List of the most commonly used cue words for reasons and conclusions:

Cue words signaling reasonsSince In view ofFor first, secondBecause in the first (second) placeAs shown by may be inferred fromAs indicated by may be deduced fromGiven that may be derived fromAssuming that for the reason that

Cue words signaling conclusions

Therefore thenThus in follows thatHence thereby showingSo demonstrates that(which) show that allows us to infer that(which) proves that suggest very strongly thatImplies that you see thatPoints to leads me to believe thatAs a result allows us to deduce thatconsequently

ARGUMENTS ARE INFERENCES

• When we construct arguments, we are composing and relating the world by means of our ability to infer.

• Inferring is a thinking process that we use to reason from what we already know.

• We can also construct arguments for different purpose – we construct arguments to decide, explain, predict and persuade.

1. We construct arguments to decide

• Example:• Reason: Throughout my life, I’ve always been

interested in all different kinds of electricity.

• Reason: There are many attractive job opportunities in the field of electrical engineering.

• Conclusion: I will work toward becoming an electrical engineering.

2. We construct arguments to explain

• Example:• Reason: I was delayed leaving my house because my

dog needed an emergency walking.

• Reason: There was an unexpected traffic jam caused by motorist slowing down to view an overturned chicken truck.

• Conclusion: Therefore, I was late for our appointment.

3. We construct arguments to predict

• Example:• Reason: Some people will always drive faster than

the speed limit allows no matter whether the limit is 55 or 65 mph.

• Reason: Car accidents are more likely at higher speeds.

• Conclusion: It follows that the newly reinstated 65 mph limit will result in more accidents.

4. We construct arguments to persuade

• Example:• Reason: Chewing tobacco can lead to cancer of the

mouth and throat.

• Reason: Boys sometimes are led to begin chewing tobacco by ads for the product that feature sports heroes they admire.

• Conclusion: Therefore, ads for chewing tobacco should be banned.

EVALUATING ARGUMENTS

• In order to construct arguments, we must be skilled in evaluating the effectiveness of arguments already constructed.

• Two aspects each arguments must be investigated independently to determine the effectiveness of the arguments as a whole:1. How true are the reasons being offered to support the

conclusion?2. To what extent do the reasons support the conclusion or

to what extent does the conclusion follow from the reasons offered?

1. How true are the supporting reasons?

• The first aspect if evaluating arguments deals with trying to determine the truth of the reasons that are being used to support a conclusion.

a. Does the reason make sense?b. What evidence is being offered as part of the reason?c. Do I know the reason to be true based on my

experience?d. Is the reason based on a source that can be trusted?

2. Do the reason support the conclusion?

• In addition to determine whether the reason are true, evaluating arguments involves investigating the relationship between the reasons and the conclusion.

• When the reasons support the conclusion so that the conclusion follows from the reason being offered, the argument is valid.

• However, if the reason do no support the conclusion does not follow from the reasons offered, the argument is invalid.

• Valid arguments:– Argument in which the reasons support the

conclusion so that the conclusion follows from the reason offered.

– Example:– Reason: anything that is a threat to our health should

not be legal.– Reason: Drug is a threat to our health.– Conclusion: Therefore, drug should not be legal.

– This is a valid argument because we can assume that the reasons are true then the conclusion necessarily follows.

• Invalid arguments– Arguments in which the reasons do not support the

conclusion so that the conclusion does not follow from the reason offered.

– Example: – Reason: Ronald Reagan believes that the strategic defense

initiative Star Wars should be built to protect the American people from Russian nuclear attack.

– Reason: Ronald Reagan is the president of the United State.

– Conclusion: Therefore, the Star Wars should be built.

– This argument is not valid because even if we assume that the reasons is true, the conclusion does not follow.

FORMS OF ARGUMENTS

• There are two major types of argument forms which are deductive arguments and inductive arguments.

1. Deductive arguments.– Argument form in which one reasons from premises that

are known or assumed to be true to a conclusion that follows logically from these premises.

• The deductive argument is the one most commonly associated with the study of logic.

– Example:– Reason/Premise: All men are mortal.– Reason/Premise: Socrates is a man.– Conclusion: Therefore, Socrates is mortal.

Common valid deductive forms:Applying a general rule:1. Socrates syllogism• Whenever we reason by using the form illustrated by

the valid Socrates syllogism, we are using the following arguments structure:– Premise: All A (men) are B (mortal)– Premise: S is an A (Socrates is a man)– Conclusion: Therefore, S is B. (Socrates is mortal)

2. Modus Ponens• “Affirming the antecedent” – Premise: I prepared thoroughly for the exam.– Conclusion: Therefore, I will do well in the exam.

• When we reason like this, we are using the following arguments structure:– Premise: If A (I have prepared thoroughly), then B (I will do

well).– Premise: A (I have prepared thoroughly)– Conclusion: Therefore, B (I will do well).

3. Disjunctive syllogism• The term disjunctive means presenting several

alternatives.

– Premise: Either I left my wallet on my dresser or I have lost it.

– Premise: The wallet is not on my dresser.