Answer two critical thinking questions
HERE IS BACKGROUND ON INFORMATION;
WHY DO PREMISES IN AN ARGUMENT NEED TO BE TRUE?
A fundamental principle in critical thinking is that the premises of an acceptable argument must be true. If the premises of an argument are false, you can reject the argument. Everyone accepts this principle—you will never find a critical thinking text in which the principle is denied. But WHY is it true? WHY do the premises of an argument need to be true? Can’t an argument be acceptable if the premises are false? (Define an acceptable argument to be one in which you are rational to believe the conclusion of the argument.) NO!
Although this fundamental principle is universally accepted, virtually no critical thinking text explains why it is true—why premises must be true. You will learn that acceptable arguments require two things: the premises are true and the premises adequately support the conclusion. If premises are true, that is a necessary but not sufficient condition for the acceptability of the argument. Similarly, if the premises provide good support for the conclusion, that is a necessary, but not sufficient condition for the acceptability of the argument.
Further, the truth of the premises has nothing to do with how good the premises support the conclusion—with how good the premises are as reasons to believe the conclusion. Just because a premise is true does not make it a good reason to believe the conclusion. You have already seen why this is so in the slides and in the first chapter of the text.
Now let’s see why premises in an argument need to be true. Consider the following argument:
Argument A
Premise: The test for the disease is positive.
Conclusion: You have the disease.
Let’s not worry about how well that premise supports the conclusion—let’s not worry about whether the premise is a good reason (or not ) to believe the conclusion. SUPPOSE THE PREMISE IS FALSE? What, then? Well, if the premise is false, then you do not have the information expressed by the sentence ‘The test for the disease is positive.’ Instead, you have the information expressed by the sentence ‘The test for the disease is negative.’ These are two different sentences. Consider the following argument:
Argument B
Premise: The test for the disease is negative.
Conclusion: You have the disease.
Argument B is different from argument A. They are two different arguments. Although you may think you have argument A, if the premise is false, you really have argument B. Only if the premise is true do you have argument A.
However, even if you know that the premise is false, you are still looking at the words ‘The test for the disease is positive.’ Thus, you mistakenly think you still have argument A, when, in fact, you do not. If the premise is false you DO NOT have argument A. You have argument B.
That is why you need the premises in your argument to be true. If they are not true, you have a rather different argument. It is easy to see why the premises being true is a necessary condition for a good—or acceptable—argument. If the premises are not true, you have a different argument. You need your premises to be true to ensure that you have the argument you think that you have, and not another argument.
The truth of premises only tells you what information you have–what information is contained in your premises. It tells you nothing else. In particular, it tells you nothing about how well those premises support (are evidence for) the conclusion of the argument.
1. Thought question: Can you think of a sentence which, when negated, says the same thing as the original, unnegated sentence? Or is that impossible? Discuss. Either find such a sentence, or explain why it is impossible to find such a sentence.
2. Test your understanding. In the textbook I say that the truth of the premsies of an argument has nothing to do with how well those premises support the argument’s conclusion. Put another way: the truth of the premises has nothing to do with how good those premises are as reasons to believe the conclusion (the claim the argument makes). The truth of premises only tells you what information you have in your premises, and nothing else. In a few paragraphs, explain WHY this is so.
