John McCardell of Middlebury College presents the following premises in his argument: (1) the minimum-21 drinking law has created a culture of dangerous and unsupervised binge-drinking; (2) the minimum-21 drinking law is impossible to enforce; and (3) 18-year-olds in this country are trusted to vote, perform jury duty, and serve in the military. Which of the following represents the conclusion he reaches?
· The drinking age should be lowered to 18.
· Underage drinking should be discouraged before it leads to more deaths.
· There should be no minimum drinking age.
· The drinking age should remain at 21.
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To what extent do you agree with the logic that when laws are too difficult or expensive to enforce, we should dispense with them? Provide at least one example or counter-example to demonstrate why you feel that way.
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The Gordie Foundation speaks of the death of a student who died of alcohol poisoning. What is their conclusion?
· The minimum-21 drinking law is only a first step in the battle against alcohol abuse.
· The minimum-21 drinking law should be left alone.
· The minimum-21 drinking law should be raised even higher.
· The minimum-21 drinking law leads to reckless behavior.
Chuck Hurley, the executive director of MADD, argues that the drinking age should stay at 21. Which of the following does Hurley use to support his conclusion?
· an anecdote about an avoidable tragedy in which an 18-year-old died from binge drinking
· statistics from the Surgeon General indicating how many Americans under the age of 21 die each year of alcohol-related causes
· a video clip of Ronald Reagan demonstrating proof that it was a good idea to raise the drinking age
· statistics showing how driving fatalities go down when the drinking age is increased and up when the drinking age is decreased
Many complex societal issues involve numerous competing arguments rather than a single, straightforward, indisputable answer. How does Leslie Stahl summarize the “conundrum” of the minimum-21 drinking law?
Arguments / 3.3 Deduction Questions: 0 of 5 complete (0%) | 0 of 3 correct (0%)
After you know you’re looking at an argument and understand its parts, the next step is to figure out which type it is. Some arguments conclude that something is definitely true, while other arguments conclude that something is probably true. An argument with a logical structure that offers certainty, provided the premises are true, is called a deductive argument. Conversely, the premises of an inductive argument might provide strong evidence in support of a conclusion, but they do not guarantee the truth of the conclusion with certainty.
|Deductive arguments are those that offer certainty. They usually use general premises to draw a specific and logically necessary conclusion.||Inductive arguments use two or more premises to support a tentative conclusion. They usually start with specific observations that combine to give reasonable certainty to a general conclusion.|
Like any argument, deductive arguments come in a variety of forms when found in everyday speech and writing, but when it comes time to evaluate deductive arguments, they’re usually translated into a standard form. While there are several types of deductive arguments, the examples on this page will be categorical syllogisms, which are deductive arguments that use two premises and a conclusion to make a claim about a whole class or category of items. The following is an example of a categorical syllogism:
Premise: Some ballerinas are not redheads. Premise: All ballerinas are dancers. Conclusion: Therefore, some dancers are not redheads.
A good deductive argument is referred to as sound. To be considered sound, a deductive argument must meet two qualifications:
1. The argument must have a valid structure.
2. All premises must be true.
To evaluate the structural validity, you look at the argument as a whole, not just the premises as individual statements. A valid argument is one in which the conclusion logically follows from the premises. Consider the following example of an invalid argument:
Premise: All chickens are domesticated animals. Premise: All cows are domesticated animals. Conclusion: Therefore, all cows are chickens.
When you see an argument like this one where the premises are obviously true while the conclusion is obviously false, it generally means that they don’t support the conclusion that is being made. In this case, because the argument doesn’t make a claim about domesticated animals as a whole category, it doesn’t necessarily follow that all cows are chickens. In other words, it’s possible to be a domesticated animal without being a chicken, and it’s possible to be a domesticated animal without being a cow. In fact, it’s possible to be a domesticated animal without being a chicken or a cow.
To reach the conclusion that all cows are chickens, you would first have to provide a premise about all domesticated animals, such as, “All domesticated animals are cows.” However, at that point, though you would have a valid structure, one of the premises would be untrue, so it would still be an unsound argument.
Because determining validity in your head is often so difficult, logicians have developed rules to systematically evaluate syllogisms. Learning these syllogistic rules can help you evaluate syllogisms more readily.
In addition to evaluating the structural validity of a deductive argument, you must also investigate the truth of the premises before you can pronounce it sound.
When evaluating deductive arguments, it is important to look at each individual premise and ask yourself if the statement is accurate, doing research if necessary. No matter how logical the argument sounds, if one or more of the premises is false, the entire argument is unsound.
Premise: All presidents of the United States are people with tattoos. Premise: Benjamin Franklin was a president of the United States. Conclusion: Therefore, Benjamin Franklin was a person with a tattoo.
In the syllogism above, the reasoning is solid, but since both the first and second premises are false, the argument is not sound. Even if just one of the premises were false, the argument would still be unsound.
Since the whole point of deductive reasoning is to find certain truth, it’s important to ask yourself if the premises in a deductive argument are completely true, all the time. This need for your audience to accept the truth of your premises before they can be asked to accept your conclusion as certain truth is why making sound deductive arguments about controversial issues is often so difficult.
Premise: Any practice in the United States that violates the rights guaranteed in the U.S. Constitution should be illegal. Premise: The death penalty violates the rights guaranteed in the U.S. Constitution. Conclusion: Therefore, the death penalty should be illegal.
Since the premises logically support the conclusion, it is likely that people on both sides of the death penalty debate would agree that this is a valid argument.
However, not everyone would accept that it is a sound argument, because some would find the truth of the second premise to be contentious. In fact, some would argue with the truth of the first premise as well.