GMAT Critical Reasoning: How to Strengthen an Argument

Written by Kelly Granson. Posted in GMAT Study Guide

images1If you are already familiar with GMAT Critical Reasoning questions of the Assumption or Weaken type, mastering Strengthen problems will not present much of a challenge. This question type, usually straightforward, asks you to support a conclusion or a plan presented in the argument. Like its Weaken and Assumption counterparts, this question requires a clear analysis of the argument and a systematic critical evaluation of the answer choices.

How to recognize a strengthen question

You can be absolutely certain that you are dealing with a Strengthen problem if you see a question stem similar to one of the following:

Which of the following, if true, most strongly supports the conclusion above?

Which of the following, if true, does most to justify the researchers' prediction?

Which of the following, if true, provides the best reason for believing that the new strategy will be successful?

Although easily recognizable, Strengthen questions can be confused with those that ask you to draw a conclusion or make an inference, which sometimes also use the word support (as in the argument above best supports which of the following statements?) However, they ask you to support one of the answers with the information IN the argument, whereas Strengthen questions require doing the reverse: instead of an answer choice supported BY the argument, you must find an answer choice that supports the argument.

How to analyze a strengthen argument

Like Assumption and Weaken problems, a Strengthen argument typically will consist of a premise or two plus a conclusion based on the information in the premises. Occasionally, the conclusion might be found in a question stem rather than in the argument itself, but this does not affect the logic of solving the problem.

The first step in effectively strengthening an argument is to identify its conclusion. Even though some questions might ask you to support the whole argument, not specifically its conclusion, remember that it is still the author's opinion that we want to strengthen.

After you have separated the premises from the conclusion, look for a weakness in the reasoning. If you spot a potential flaw or a gap in the argument, you can strengthen its conclusion by selecting an answer choice with new information that at least partially closes this gap. Sometimes it helps to think of what assumptions the author makes and see whether any of them is unsupported. In those cases, you can strengthen the argument by proving that an assumption is actually valid.

Look at the following simple example:

Dietician: A kiwi contains twice as much vitamin C as an orange does. Nevertheless, those seeking to get their daily dose of Vitamin C from fruits do not need to replace oranges with kiwis in their diet.

Which of the following, if true, would lend the most support to the dietician's conclusion?

A premise here is that a kiwi has more Vitamin C than an orange does. The dietician concludes, however, that people don't need to replace oranges with kiwis. Is it clear from this argument why replacement isn't necessary even though kiwis can supply more Vitamin C? No, so your goal is to find some additional information explaining why people may stick to oranges after all.

Another useful thing to know is that many arguments use information from analogies and surveys in their premises. In this case, answer choices that support the validity or soundness of such data are usually correct. For example, if the author makes a general conclusion based on information about a certain group of people, there's always a possibility to attack this argument by claiming that the given group of people does not represent the majority. By contradicting that claim, you'll strengthen the argument and protect it from such attacks.

How to pick the right choice

A correct answer choice will rarely make the conclusion one hundred percent true. Therefore, it is essential that you compare answer choices and pick the one that does the best job of strengthening the argument, even if it makes the conclusion only a little more likely to be true.

Look at the answer choices for the Kiwi versus Orange question:

A. Oranges also contain several other vitamins that are beneficial to human health.

B. In certain regions, kiwis might be harder to obtain than oranges.

C. Unlike that derived from oranges, Vitamin C from kiwis is easier for a human body to process.

D. An orange contains a necessary daily dose of Vitamin C.

E. Neither a kiwi nor an orange provides a sufficient daily dose of vitamin C.

Here the best choice is D because it explains why people need not necessarily switch from oranges to kiwis: a dose of Vitamin C from an orange is already enough and there is no need for more Vitamin C daily.

How to avoid the wrong choices

Typically wrong answers for Strengthen questions are like those for the Weaken type. They may have no tie to the conclusion, repeat the information presented in the premises, or attempt to explain why else a plan might work, but they fail to fix the weakness of the conclusion or validate the assumptions of the argument. Choices A and B in the kiwi/orange argument belong to this category; they explain why oranges are better than kiwis but without reference to Vitamin C.

Other wrong choices might go in the opposite direction and weaken the conclusion instead of strengthening it. Choices C and E above give reasons why kiwis may be preferred to oranges and therefore SHOULD replace oranges. Be careful with such options. Because of their seeming relevance to the conclusion, they can be very tempting, especially when you are under stress and pressed for time.

The last category of wrong answers includes those that appeal to your real-life experience. Remember, you are not assessing the plausibility of answer choices, or their real-life truthfulness; all that matters is the argument's structure and the soundness of its reasoning.

In summary, you strengthen an argument in three simple steps:

1) Identify the argument's conclusion.

2) Find the argument's weakness or an unsupported assumption.

3) Pick the choice that best fixes the weakness or supports the assumption, avoiding those that contain irrelevant information or go in the wrong direction, and keeping in mind that you don't have to prove the argument, just strengthen it.

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