# Strengthen the Argument

The Assumption Family is the biggest of the three Critical Reasoning Families.

Two other question types that come within the purview of this family are “Strengthen the Argument” and “Weaken the Argument.

We will be covering the “Strengthen the Argument” question type here.

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Reiterating:

1. Assumptions are something an author must believe to be true in order to draw his or her conclusion. These assumptions are never really stated explicitly in the argument.
2. All assumption arguments will contain a “core”; i.e. a conclusion and one or more premises that lead to it.
3. All assumption arguments will include at least one (and probably more than one) unstated assumption.

Much like the “Find the Assumption” question type, “Strengthen the Argument” questions are very popular on the GMAT.

The “Strengthen the Argument” question type demands that you find a new piece of information that, if added to the existing argument, will make the conclusion more likely to be true.

So, how is the Strengthen the Argument variety of question any different from the Find the Assumption variety?

Well, on a Strengthen question, you will be asked to look into a new piece of information that does not have to be true at all (unlike the Find the Assumption questions). But, if this information is true, then it will accentuate the conclusion and make it more logically valid.

Most often, the question stem of all Strengthen questions will contain some form of the words “strengthen” or “support”, as well as the phrase “if true”. These questions may occasionally lack the exact phrase “if true”, but some other wording will provide a similar meaning; wording that indicates that the answer can be “effectively achieved” or” successfully accomplished.

Let’s have a look at an example:

Astronomer: Most stars are born in groups of thousands, each star in a group forming from the same parent cloud of gas. Each cloud has a unique, homogeneous chemical composition. Therefore, whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.

Which of the following, if true, would most strengthen the astronomer’s argument?

(A) In some groups of stars, not every star originated from the same parent cloud of gas.

(B) Clouds of gas of similar or identical chemical composition may be remote from each other.

(C) Whenever a star forms, it inherits the chemical composition of its parent cloud of gas.

(D) Many stars in vastly different parts of the universe are quite similar in their chemical compositions.

(E) Astronomers can at least sometimes precisely determine whether a star has the same chemical composition as its parent cloud of gas.

Let’s break it down:

Conclusion: “Therefore, whenever two stars have the same chemical composition as each other, they must have originated from the same cloud of gas.”

Premise: “Most stars are born in groups of thousands, each star in a group forming from the same parent cloud of gas. Each cloud has a unique, homogeneous chemical composition.”

We can understand the following from the above argument:

The given conclusion considers the implication of two stars having similar chemical composition, whilst assuming on a basic level that if he/she were to compare the chemical composition of the stars and the gas cloud they seem to have originated from, then they would be exactly the same.

Any answer choice that supports the author’s assumption, will strengthen the argument.

Before you consider each answer choice in turn, remember that your focus should lie with the chemical composition of the stars, and how if they’re similar to each other and to the origin gas cloud, they’re likely to have originated in the same cluster.

Option A cannot clearly portray a significant relevance between where stars are born (different clouds of gas) and whether they have the same chemical composition. The ambiguity of this option is in fact rather likely to weaken the argument, than strengthen it.

Option B focuses on how far apart clouds of gases are from each other; something that has no relevance to the chemical composition.

Option D also deviated from the main focus of the argument by talking about stars in different parts of the universe.

In the case of option E, any findings on the astronomers’ part could strengthen or weaken the argument. Merely their ability to somewhat precisely determine whether a star has the same chemical composition as its parent cloud of gas, does little to support the author’s conclusion.

Option C is pretty clearly the winner, because it very explicitly states that “Whenever a star forms, it inherits the chemical composition of its parent cloud of gas.”. Hence, C is the answer.

Another example:

One summer, floods covered low-lying garlic fields situated in a region with a large mosquito population. Since mosquitoes lay their eggs in standing water, flooded fields would normally attract mosquitoes, yet no mosquitoes were found in the fields. Diallyl sulfide, a major component of garlic, is known to repel several species of insects, including mosquitoes, so it is likely that diallyl sulfide from the garlic repelled the mosquitoes.

Which of the following, if true, most strengthens the argument?

(A) Diallyl sulfide is also found in onions but at concentrations lower than in garlic.

(B) The mosquito population of the region as a whole was significantly smaller during the year in which the flooding took place than it had been in previous years.

(C) By the end of the summer, most of the garlic plants in the flooded fields had been killed by waterborne fungi.

(D) Many insect species not repelled by diallyl sulfide were found in the flooded garlic fields throughout the summer.

(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.

Breaking it down:

Conclusion: “…so it is likely that diallyl sulfide from the garlic repelled the mosquitoes.

Premise(s): “mosquitoes lay their eggs in standing water, flooded fields would normally attract mosquitoes, yet no mosquitoes were found in the fields. Diallyl sulfide, a major component of garlic, is known to repel several species of insects, including mosquitoes.”

We can understand the following from the above argument:

If we are to go by the assumption stated above, any information that further solidifies the notion that no other independent factor in those fields could have contributed to the warding off of the mosquitoes, will strengthen the author’s argument.

From the given answer choices, options B and E actually weaken the argument because B suggests that the mosquito population took a hit that year, dismissing the significance of garlic and E highlights the mosquitoes’ susceptibility to toxins in plants rather than garlic. Option A would only be relevant if the author had been speaking of onion fields in his argument. Though option C talks of the garlic directly, it does not clearly indicate how the diminishing of the garlic plants would affect the amount of diallyl sulfide in the flooded fields.

Hence, the answer is option D, because it clearly provides evidence that there was no factor other than diallyl sulfide that reduced insect populations in the flooded garlic fields.

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