Reading Comprehension Challenge: Deconstruct the Argument

Argument passages in GRE Reading Comp vary in complexity. If you’re asked to weaken or strengthen an argument, then the passage probably contains just one conclusion. But if you’re asked to identify the roles that parts of the passage play in an argument, then the text may include a main conclusion and an intermediate conclusion. See whether you can spot the conclusion(s) in this passage.

Reading Comprehension: Analyzing Argument Structure
Difficulty Level: 3 (Medium)

In The Practice Book for the Paper-based GRE, a fairly difficult question asks you to classify the parts of an argument that’s about soil moisture and melon crop sweetness. (See §3, 14.) Just 40% of test takers got the question right when it was on a real exam. Here’s the same question (and answer choices) applied to an argument passage that has the same structure but different subject matter.

The Explanation

You know the passage contains an argument. As you read the text, you get the sense that it’s trying to convince you of something. An often-used conclusion indicator—”therefore”—cements this impression. Even if you finished the passage and didn’t realize you’d just read an argument, the question leaves no doubt: “In the argument given…”

What’s more, you can tell the question is about the argument’s structure. It asks you the “roles” played by the bolded parts of the passage. Scanning the answer choices, you see that each option mentions either an “intermediate conclusion” or the “conclusion of the argument as a whole,” so the passage very likely contains a linked argument—that is, two or more arguments linked together.

In the simplest case, and the case you’re most likely to see on the GRE, a linked argument includes one subargument plus the main argument. The subargument supports an intermediate conclusion, and this intermediate conclusion serves as a premise in the main argument, the final defender of the main conclusion. Combined, the subargument and the main argument make up “the argument as a whole,” and “the conclusion of the argument as a whole” is the main conclusion.

So, given the wording of the question, you know you need to deconstruct an argument and, based on the wording of the answer choices (if not your sense of the passage), you know it’s probably two-arguments-in-one.

Step 1: Find the main argument. Start by finding the main conclusion. It may be marked by an indicator word. In the passage, the last sentence uses the word “therefore,” a common conclusion indicator.

Therefore, levels of atmospheric CO² should fall at least slightly as glacial melting in Antarctica continues.

But there’s another conclusion indicator present. The second bolded sentence opens with the phrase “It follows that…” and, by definition, an argument’s conclusion is supposed to ‘follow from’ its premises.

It follows that the warm ocean waters around Antarctica host growing populations of phytoplankton.

Each of these claims is very likely a conclusion. But which one is the main conclusion? Take the claim about phytoplankton. Does the argument as a whole intend to convince you that phytoplankton are thriving in the Antarctic Ocean? No, the conclusion about phytoplankton is an intermediate step toward the main conclusion that glacial melting in Antarctic will reduce atmospheric CO². Here’s a simple paraphrase of the main argument.

• Premise: Warm waters in the Antarctic Ocean breed phytoplankton.
• Premise: Phytoplankton consume atmospheric CO².
• Main Conclusion: Melting Antarctic glaciers reduce atmospheric CO².

With this argument in view, you can eliminate (A), (B), and (D). Option (A) claims that the main conclusion is the first bolded sentence—”Ice is slowly sliding off the continent…” Options (B) and (D) imply that the second bolded sentence—”It follow that the warm ocean waters…”—opposes, rather than supports, the main conclusion.

There’s something missing from this reconstruction of the main argument—namely, about half the passage, including the first bolded sentence. That’s okay. You just need to figure out what the rest of the text is doing. Perhaps it’s a subargument after all?

Step 2: Find the subargument (if any). Start by looking for an intermediate conclusion. You already a have a clear candidate.

It follows that the warm ocean waters around Antarctica host growing populations of phytoplankton.

Call this statement PG, as in ‘phytoplankton growth’. For PG to be an intermediate conclusion, two things must be true:

1. PG is offered as support for the main conclusion. ✓
2. PG is based on its own set of premises. ?

The first condition has been met: PG is a premise in the main argument. What about the second condition? Check the passage for statements that could lead you to believe that phytoplankton are flourishing around Antarctica. The opening three sentences do the job. Here’s a quick summary of the subargument.

• Premise: Warm waters in the Antarctic Ocean melt Antarctic glaciers.
• Premise: Melting Antarctic glaciers deposit iron in the Antarctic Ocean.
• Premise: Iron helps phytoplankton grow.
• Intermediate Conclusion: Warm waters in the Antarctic Ocean breed phytoplankton.

The second premise—”Melting Antarctic glaciers deposit iron…”—is a paraphrase of the first boldface portion of the passage—”Ice is slowly sliding off the continent…” Thus, the correct answer is (C): the first bolded part about glacial ice and iron supports an intermediate conclusion, and the intermediate conclusion is the second bolded part about growing populations of phytoplankton.

When a Reading Comp question is solely about an argument’s structure, expect that structure to be complex. A linked argument is a good bet, so make sure you’re ready for longer chains of reasoning.

In the meantime, how about you try deconstructing some shorter, simpler arguments? The catch is you’ll also have to evaluate them. Check out these posts:

• GRE Reading Comp Challenge: Weaken an Argument
• GRE Reading Comp: Strengthen an Argument.

Photo: “Thwaits Glacier” by NASA – http://www.jpl.nasa.gov/news/news.php?release=2014-148 JPL. Licensed under Public Domain via Commons.