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Moore−Parker: Critical Thinking, Eighth Edition

7. The Anatomy and Varieties of Arguments


© The McGraw−Hill Companies, 2007



When a premise is unstated, try to supply a reasonable assumption that would make the argument valid or strong. I If you have trouble tracking the parts of an argument that appears in a written passage, try diagramming the passage. I

Exercise 7-1
Indicate which blanks would ordinarily contain premises and which would ordinarily contain conclusions.



1. a , and b . Therefore, c 2. a . So, since b , c . 3. a , because b . 4. Since a and b , c . 5. a . Consequently, b , since





Exercise 7-2
Identify the premises and conclusions in each of the following arguments.

L 1. Since all Communists are Marxists, all Marxists are Communists. 2. The Lakers almost didn’t beat the Kings. They’ll never get past Dallas. 3. If the butler had done it, he could not have locked the screen door. Therefore, since the door was locked, we know that the butler is in the clear. L 4. That cat is used to dogs. Probably she won’t be upset if you bring home a new dog for a pet. 5. Hey, he can’t be older than his mother’s daughter’s brother. His mother’s daughter has only one brother. 6. Moscone will never make it into the state police. They have a weight limit, and he’s over it. L 7. Presbyterians are not fundamentalists, but all born-again Christians are. So no born-again Christians are Presbyterians. 8. I guess he doesn’t have a thing to do. Why else would he waste his time watching daytime TV? 9. “There are more injuries in professional football today than there were twenty years ago,” he reasoned. “And if there are more injuries, then today’s players suffer higher risks. And if they suffer higher risks, then they should be paid more. Consequently, I think today’s players should be paid more,” he concluded. L 10. Let’s see . . . If we’ve got juice at the distributor, the coil isn’t defective, and if the coil isn’t defective, then the problem is in the ignition switch. So the problem is in the ignition switch.

Moore−Parker: Critical Thinking, Eighth Edition

7. The Anatomy and Varieties of Arguments


© The McGraw−Hill Companies, 2007




Exercise 7-3
Identify the premises and the conclusions in the following arguments.

L 1. The darned engine pings every time we use the regular unleaded gasoline, 2. 3. but it doesn’t do it with super. I’d bet that there is a difference in the octane ratings between the two in spite of what my mechanic says. Kera, Sherry, and Bobby were all carded at JJ’s, and they all look as though they’re about thirty. Chances are I’ll be carded too. Seventy percent of freshmen at Wharfton College come from wealthy families; therefore, probably about the same percentage of all Wharfton College students come from wealthy families. When blue jays are breeding, they become very aggressive. Consequently, scrub jays, which are very similar to blue jays, can also be expected to be aggressive when they’re breeding. A cut in the capital gains tax will benefit wealthy people. Marietta says her family would be much better off if capital gains taxes were cut, so I’m sure her family is wealthy. According to Nature, today’s thoroughbred racehorses do not run any faster than their grandparents did. But human Olympic runners are at least 20 percent faster than their counterparts of fifty years ago. Most likely, racehorses have reached their physical limits but humans have not. It’s easier to train dogs than cats. That means they’re smarter than cats. “Let me demonstrate the principle by means of logic,” the teacher said, holding up a bucket. “If this bucket has a hole in it, then it will leak. But it doesn’t leak. Therefore, obviously it doesn’t have a hole in it.” I know there’s a chance this guy might be different, but the last person we hired...
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