Silencing The Doubters: Negative Assumptions On GMAT Critical Reasoning

by on September 5th, 2009

Arguments on the Critical Reasoning section of the GMAT have three elements—a handful of pieces of evidence, a conclusion, and assumptions. The first two elements are quantifiable— they’re written right there in the argument. However, assumptions are… a bit difficult to count. In fact, they’re impossible to count; technically, there are an infinite number of assumptions behind any argument. How can this be?

Any unstated—but necessary—premise in an argument is an assumption. “Unstated” is the easy part: It makes sense that there are an infinite number of unstated premises in any argument. The “necessary” quality is a little trickier: How can there be infinite necessary premises behind one little argument?

Let’s look at an example:

You: “I have plane tickets to Peru next week. I’ve gone to Peru every year of my life, and always loved it. Therefore, I’m sure I’ll have a great time next week.”

Your annoying little brother: “What if you get run over by a bus tomorrow?”

Your mind: “What if your plane crashes?”

Your mother: “What if you get a tropical disease?”

News article: “What if Peru has totally changed in the last year?”

Chicken Little: “What if the sky falls?”

Your revised argument: “OK, if I don’t get run over by a bus, and my plane doesn’t crash, and I don’t get a tropical disease, and Peru has not changed significantly in the last year, and the sky doesn’t fall, then I’ll have a great time.”

Note that your revised argument has added five new conditional statements, each one bringing what was once an unstated assumption into the light. Perhaps more importantly, these assumptions are all framed as negative: (“If I don’t get a tropical disease”). This is one of the ways in which infinite assumptions fit into an argument; because the arguer must assume that millions of things don’t happen.

Now, to be clear; there are also many positive assumptions in this argument (That I will actually get on the plane, that the plane will actually arrive in Peru, etc.). However, the lion’s share of the assumptions come from the negative side; in essence, these assumptions are about silencing the doubters and negating the weakeners; when your mother warns about a tropical disease, you must reassure her that you’re assuming that her fears will not come true, which is why your conclusion still works. Remember, there are an infinite number of such doubters, all trying to poke holes in the argument.

Let’s make this argument into a GMAT question and see how this same logic works:

The city council of Northwood has decided to reward several of Northwood’s most prominent and active community leaders with an all-expense paid vacation to Peru next month. The city council members claim that this vacation is an appropriate reward for the community leaders, citing that all of the community leaders have been to Peru in the past and enjoyed themselves; thus, claim the city council members, they will clearly enjoy themselves on this all-expense paid vacation.

All of the following provide an assumption upon which the city council members’ argument relies EXCEPT?

a)      The community leaders will not suffer any local accidents in the next month that prevent them from embarking on the vacation

b)      The mode of transportation upon which the community leaders will travel to Peru will not suffer any mechanical difficulties that impede its safe arrival

c)       The vacationing community leaders will not contract a debilitating disease endemic to Peru

d)      Peru has not significantly changed in the period since the community leaders’ last visit

e)      The price of vacationing in Peru has not risen significantly since the community leaders’ last visit, making many of the activities they enjoyed significantly more expensive

Answers A through D are all assumptions that quell the doubters, and they’re all framed negatively. ONLY if none of those things happen will the city council member’s conclusion (that the community leaders will enjoy themselves) be true.

Answer E, by the way, although it is framed negatively, is not an assumption, and is the correct answer. This is because the trip is “all-expense paid,” so the rising price should not affect the vacationing community members’ enjoyment.

If this is unclear, you always want to remember to use the assumption denial test. As with any other assumptions, denying negative assumptions will break the conclusion. Let’s test this with answer choice A:

Negation of (a): “The community leaders will suffer local accidents in the next month that prevent them from embarking on the vacation”

Well, if that’s true, than the conclusion will certainly not remain true. Community leaders that do not go on a vacation cannot enjoy that vacation.

1 comment

  • Shouldn't option E, read like " The price of vacationing in Peru 'has' (and not has not) risen significantly since the community leaders’ last visit, making many of the activities they enjoyed significantly more expensive", for it to be the correct option?

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