Brief Guide To Logic And Argumentation Essay 4

When a philosopher tackles a question, her aim is not just to answer it. Her aim is to provide an argument for her answer and so to present her audience with reasons for believing what she believes. When you read a philosophical text, your main job is to identify and assess the author’s arguments. When you write a philosophy paper, your main job is to offer arguments of your own. And because philosophy is an especially reflective discipline—every question about philosophy is a philosophical question—philosophers have turned their attention to this phenomenon. What is an argument? What is a good argument? How can we tell whether an argument is a good one? The aim of this brief guide is to introduce some of the tools that philosophers have developed for answering these questions. But be warned: some of what follows is controversial, and many of the most important questions in this area remain wide open. It may be unsettling to discover that even at this elementary stage, philosophy raises questions that centuries of reflection have not resolved. But that is the nature of the subject, and you might as well get used to it.

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1. WHAT IS AN ARGUMENT?
An argument is a sequence of statements. The last claim in the sequence is the conclusion. This is the claim that the argument seeks to establish or support. An argument will usually include one or more premises: statements that are simply asserted without proof in the context of the present argument but which may be supported by arguments given elsewhere. Consider, for example, the following argument for the existence of God:

ARGUMENT A
1. The Bible says that God exists.

2. Whatever the Bible says is true.

3. Therefore, God exists. Here the premises are (1) and (2), and statement (3) is the conclusion. Brief Guide To Logic And Argumentation Essay 4

Now, anyone who propounds this argument will probably realize that his prem ises are controversial, so he may seek to defend them by independent arguments. In defense of (2) he may argue:

ARGUMENT B
4. The Bible has predicted many historical events that have come to pass.

5. Therefore, whatever the Bible says is true.

These two arguments may be combined:

ARGUMENT C
6. The Bible has predicted many historical events that have come to pass.

7. Therefore, whatever the Bible says is true.

8. The Bible says that God exists.

9. Therefore, God exists. Here the premises are (6) and (8). Statement (7) is now an intermediate conclusion, supported by premise (6), and the conclusion of the argument as a whole is (9), which is in turn supported by (7) and (8). It can be useful to make all of this explicit by writing the argument out as follows: ARGUMENT C, annotated

10. The Bible has predicted many historical events that have come to pass.

· [premise]

11. Therefore, whatever the Bible says is true.

· [from (6)]

12. The Bible says that God exists.

· [premise]

13. Therefore, God exists.

· [from (7), (8)]

14. when you are reading a philosophical text with an eye toward identifying the author’s argument, it is extraordinarily important (and often quite difficult) to distinguish the author’s premises—the propositions she takes for granted as a starting point—from her conclusions. Why is this important? If a statement is meant as a conclusion, then it is fair to criticize the author if she has failed to give a reason for accepting it. If, however, a statement is a premise, then this sort

15. f criticism would not be fair. Every argument must start somewhere. So you should not object to an argument simply on the ground that the author has not proved her premises. Of course, you can object in other ways. As we will see, it is perfectly fair to reject an argument when its premises are false, implausible,

16. r defective in some other way. The point is rather simply this: since every argu- ment must have premises, it is not a flaw in an argument that the author has not argued for her premises.

· All of this is trivial when the arguments are simple and neatly packaged. But

Rules of thumb: If a sentence begins with “hence” or “therefore” or “so,” that is a clue that it functions as a conclusion. If a sentence begins with “Let us assume that . . .” or “It seems perfectly obvious that . . .” or “Only a fool would deny that . . . ,” this is a clue that it functions as a premise.

Exercise: Consider the following passage. What are the premises? What is the main conclusion?

Everyone knows that people are usually responsible for what they do. But you’re only responsible for an action if your choice to perform it was a free choice, and a choice is only free if it was not determined in advance. So we must have free will, and that means that some of our choices are not determined in advance.

2. VALIDITY
An argument is valid if and only if it is absolutely impossible for its premises to be true and its conclusion false. In our examples, argument a is clearly valid. If the premises are true—if the Bible is infallible, and if the Bible says that God exists—then God must certainly exist. There is no possible situation—no possible world—in which the premises of the argument are true and the conclusion false. Argument b, by contrast, is clearly invalid. It is easy to imagine a circumstance in which the Bible makes many correct predictions about historical events while remaining fallible on other matters. When an argument is valid, we say that the premises entail or imply the conclusion, or, equivalently, that the conclusion follows from the premises. Brief Guide To Logic And Argumentation Essay 4

This concept of validity is a technical one, and some of its applications may strike you as odd. Consider:

ARGUMENT D
All philosophers are criminals. All criminals are short. Therefore, all philosophers are short.

ARGUMENT E
God exists. Therefore, God exists.

ARGUMENT F
The moon is green. The moon is not green. Therefore, God exists.

It is easy to see that argument d is valid. The premises are false, but that is ir relevant. They could have been true, and any possible circumstance in which they are true is one in which the conclusion is also true. Argument e is also valid. Since the premise and the conclusion are identical, it is clearly impossible for the one to be true and the other false. To see that argument f is valid, note that it is obviously impossible for its premises to be true together—the moon cannot be both green and not green! But this means that it is impossible for the premises to be true and the conclusion false, and that is exactly our definition of validity.

As the examples show, a valid argument can be a lousy argument. Still, validity is an important property of arguments. Some disciplines—notably, mathematics— insist on valid arguments at every stage. In these areas, a good argument must be a proof, and a proof is a valid argument from premises known to be true. Philoso phy, like most disciplines, does not insist on proof. Yet philosophers often aspire to produce valid arguments for their conclusions, and there is a good reason for this. Begin by noting that it is always possible to turn an invalid argument, or an argument whose validity is uncertain, into a valid argument by adding premises. Suppose a philosopher offers the following argument:

ARGUMENT G
I can imagine existing without my body. (I can imagine my feet slowly and painlessly disappearing, then my knees, then my legs. . . . As my body disap pears, I lose all sensation. As my head disappears, everything goes black and silent because my eyes and ears have disappeared, but still I’m thinking about these strange events, and because I’m thinking, I must exist.)

Therefore, I am not my body.

It may be hard to say whether this is a valid argument, but we can easily turn it into an argument whose validity is beyond dispute:

ARGUMENT H
I can imagine existing without my body. If I can imagine X existing without Y, then X is not Y. Therefore, I am not my body.

A philosopher who offers argument g as a proof that human beings are not identical to their bodies probably has argument h in mind. She is probably tacitly assuming the premise that is missing in argument g but that h makes explicit. For philosophical purposes, it is often important to make these tacit assumptions explicit so that we can subject them to the bright light of scrutiny. Brief Guide To Logic And Argumentation Essay 4

When you reconstruct the argument implicit in a philosophical text, you should set yourself the task of producing a valid argument for the author’s conclusion from the author’s stated premises, supplying any missing premises that might be necessary for this purpose, so long as they are premises that the author might

have accepted. If there are many ways to do this, you will find yourself with several competing interpretations of the argument. If there is only one sensible way of doing this (as with argument g), you will have identified the author’s tacit assumptions. This is often a valuable step in your effort to assess the argument.

Exercise: Spot the valid argument(s):

(i) If abortion is permissible, infanticide is permissible.

Infanticide is not permissible. Therefore, abortion is not permissible.

(ii) It is wrong to experiment on a human subject without consent. Brief Guide To Logic And Argumentation Essay 4

· X experimented on Mr. Z.

· Z consented to this experiment. Therefore, it was not wrong for Dr. X to experiment on Mr. Z.

iii. I will not survive my death. My body will survive my death. Therefore, I am not my body.

(iv) Geoffrey is a giraffe.

If X is a giraffe, then X’s parents were giraffes. Therefore, all of Geoffrey’s ancestors were giraffes.

Exercise: The following arguments are not valid as they stand. Supply missing premises to make them valid.

(v) Every event has a cause. No event causes itself. Therefore, the universe has no beginning in time.

(vi) It is illegal to keep a tiger as a pet in New York City.

Jones lives in New York City. Therefore, it would be wrong for Jones to keep a tiger as a pet.

(vii) The sun has risen every day for the past 4 billion years. Therefore, the sun will rise tomorrow.

Check your understanding. Some statements express necessary truths: truths that could not possibly have been false under any circumstances. The truths of pure mathematics are the best examples. There is no possible circumstance in which 2 + 3 ≠ 5, so “2 + 3 = 5” is a necessary truth. With this in mind, show that an ar gument whose conclusion is a necessary truth is automatically a valid argument.