Skill in logic, reasoning and critical thinking can help protect a teenager against manipulative advertising, high-pressure sales tactics and dishonest political messages. Few U.S. public schools teach formal logic, but parents can help their teens learn how to distinguish a strong logical argument from a weak one through the use of logical exercises.
U.S. high schools used to teach formal logic as part of the standard curriculum, but in recent decades the study of logic has largely been replaced with less formal approaches to critical thinking. According to an essay by Sherri N. McCarthy-Tucker at Northern Arizona University, a study of 190 high school students found that those who had been taught formal logic did better on a test of reasoning skills than those who were taught critical thinking without formal logic. This indicates that traditional logic exercises are more effective at teaching teenagers how to reason effectively.
Syllogisms are logical arguments made up of a major premise, a minor premise and a conclusion. For example, "All teenagers hate homework. Jim is a teenager. Therefore, Jim hates homework." The first sentence is the major premise, the second sentence is the minor premise and the third sentence is the conclusion. If a syllogism is correctly constructed, it is considered logically valid even if the premises are not true. In this example, it's not actually true that all teenagers hate homework. However, if it was true that all teenagers hated homework and if it was also true that Jim was a teenager, then obviously it would have to be true that Jim hated homework. To introduce a teen to formal logic, explain how syllogisms work and encourage him to compose some of his own.
When a syllogism is poorly constructed, it is logically invalid. For instance, "All high school students want to graduate. Jim wants to graduate. Therefore, Jim is a high-school student." The major and minor premises might not be true, but that's not what makes the argument invalid. The argument is invalid because Jim might be a college student rather than a high school student. This syllogism is an example of a logical fallacy called the "undistributed middle term." Learning how to spot logical fallacies is a fun way to learn about logical reasoning.
Logical fallacies are invalid arguments. People who know how to spot the most common logical fallacies are much harder to manipulate because they can quickly see what is wrong with a particular argument. For example, "you should buy these shoes because your favorite movie star wears them" is an example of a fallacy called "the appeal to improper authority." Movie stars have no particular expertise about shoes, so the opinion of a movie star is irrelevant when buying shoes.
Spot the Fallacy
You can compose your own set of logically invalid arguments and ask your teen to name which fallacy each argument relies on, using a list of the standard fallacies. For example, "you should have a drink at the party because everyone else is doing it" is the fallacy of "appeal to popularity." The argument "Jim's political opinions must be false because Jim is a bad kid" is an example of the "ad hominem" fallacy. By using relevant examples drawn from real life, you can help your teen gain valuable critical thinking skills.