Enthymemes

In general, no one actually uses formal syllogisms when making arguments. However, deductive reasoning is something you encounter everyday—you just might not recognize deductive arguments when you hear them.

Suppose you ask your instructor why your grade is so low, and your instructor tells you, “You didn’t do your webtext homework—that’s why you’re failing my course.” What your instructor is using is something called an enthymeme, or an abbreviated deductive syllogism that contains an implied premise.

Premise: All students who don’t do their webtext homework are students who fail my course. (Implied) Premise: You are a person who didn’t do his webtext homework. Conclusion: Therefore, you are a student who will fail my course.

When people talk in enthymemes, they often leave out the implied premise because they think it’s so obvious that it doesn’t need to be stated. But it’s often important to figure out the assumed premise, because the assumption may not be as plainly true as the speaker thinks. Once you tease out the syllogism buried within an enthymeme, you may decide that the assumption the speaker is making needs a closer look.

Consider the following enthymeme:

“Fritz’s grandfather won’t know how to use Twitter—he’s eighty-eight!”

Premise: Fritz’s grandfather is an eighty-eight-year-old. (Implied) Premise: No eighty-eight-year-olds are people who know how to use Twitter. Conclusion: Fritz’s grandfather is not a person who knows how to use Twitter.

Even though the speaker never states that no eighty-eight-year-olds are people who know how to use Twitter, he implies it when he makes the leap from Fritz’s grandfather being eighty-eight to Fritz’s grandfather definitely not knowing how to use Twitter.

Arguments with enthymemes appear everywhere from casual conversations to discussions about controversial issues. The assumptions hidden in enthymemes often carry some truth to them, but they may or may not earn the guaranteed certainty of truth that comes with deductive arguments.

Answer the following questions about the material above.

Which of the following is the BEST definition of a deductive argument?

· an argument that contains the words “all,” “no,” or “some”

· an argument with premises that suggest that the conclusion is probably true

· an argument with a necessarily true conclusion, provided the premises are true

· an argument with true premises

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Consider the following syllogism:

Premise: All men are skillful drivers. Premise: Gus is a man. Conclusion: Therefore, Gus is a skillful driver.

How does it hold up in terms of truth, validity, and soundness?

· The premises aren’t true, and the argument is invalid, so the argument is unsound.

· The argument is valid, but not all of the premises are true, so the argument is unsound.

· The premises are all true, but the argument is invalid, so the argument is unsound.

· The premises are all true, and the argument is valid, so the argument is sound.

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Why is it hard to settle a debate on a controversial issue with a simple deductive argument?

 

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Isabelle says, “Since felons in this country are Americans just like the rest of us, they should be allowed to vote.” Which of the following represents the hidden assumption of her enthymeme?

· Felons from other countries are allowed to vote.

· Felons should sue for discrimination when they are not allowed to vote.

· In previous elections, felons have not been allowed to vote.

· All Americans are people with the right to vote.

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When Pedro is making his book pitch to a publisher, he says, “All the books in my series are about how to get rich fast. Trust me, they’ll sell like hotcakes.” What is the hidden assumption in Pedro’s enthymeme?

 

 

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Practice: Deduction

Deductive Arguments and Enthymemes in the Wild

In the exercises below, you will examine pieces of deductive reasoning from a variety of articles.

The following passage is an excerpt from an article titled “The Problem with Special Ed” by Jay P. Greene, originally published in the National Review Online on September 14, 2009, which questions the increase in special-education enrollments in recent years.

Use the passage below to answer the next question.

One of the reasons we know that reported disability rates lack credibility is that they vary dramatically from state to state. In New Jersey, for example, 18 percent of all students are classified as disabled, but in California the rate is only 10.5 percent. 7

The first sentence in the passage forms an enthymeme. What is the hidden assumption of that enthymeme?

· Focusing on “reported” disability rates ignores possible unreported disabilities.

· There are more students classified as disabled in eastern states than western states.

· All disability rates that vary from state to state lack credibility.

· If disability rates were the same from state to state, they would definitely be credible.

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The following passage is an excerpt from the article “Animal Rights Uncompromised: Zoos” from the “Uncompromising Stands on Animal Rights” series on the PETA (People for the Ethical Treatment of Animals) website.

Use the quoted enthymeme below to answer the next two questions.

PETA opposes zoos because cages and cramped enclosures at zoos deprive animals of the opportunity to satisfy their most basic needs. 8

Which of the following is the hidden assumption in the enthymeme above?

· PETA’s policy is to be against all zoos.

· PETA believes that zoos often lead to abnormal, neurotic, and even self-destructive behavior in animals.

· PETA opposes institutions that deprive animals of the opportunity to satisfy their most basic needs.

· PETA would approve of zoos if they didn’t keep animals in cages and cramped enclosures.

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The following passage is an excerpt from an op-ed in the Connecticut Mirror criticizing the Common Core standards implemented in Connecticut schools.

Use the quoted enthymeme below to answer the next two questions.

This standardized test of “college and career readiness” is particularly inappropriate and unreliable because not one teacher was involved in setting the learning goals.9

What is the hidden assumption in the enthymeme above?

 

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The following passage is an excerpt from an op-ed in the Los Angeles Times titled “Where are the Supreme Court Justices Hiding?” about the lack of transparency in the U.S. Supreme Court.

Use the quoted enthymeme below to answer the next two questions.

Supreme Court justices are government officials whose salaries are paid by the taxpayers, and their records, like those of the president, should be deemed public property and available for review after taking into account reasonable privacy concerns. 10

What is the hidden assumption in the enthymeme above?

 

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7 Jay P. Greene, “The Problems with Special Ed,” National Review Online, September 14, 2009.

8 People for the Ethical Treatment of Animals (PETA), “Animal Rights Uncompromised: Zoos”

9 Ann Policelli Cronin, “Buyers Beware (Of Common Core)”, Connecticut Mirror, April 9, 2014.

10 Eric J. Segall, “What are the Supreme Court Justices Hiding?”, LA Times, May 5, 2014.

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