<em>This post was written by Sean Murphy, one of Knewton's expert <a href="http://www.knewton.com/gmat">GMAT prep</a> teachers. For more expert GMAT help, check out the Knewton <a href="http://www.knewton.com/blog/gmat/">GMAT blog</a>. </em>
Critical Reasoning Assumption questions ask you to identify an unspoken assumption made by the argument’s author. On these types of questions, one of the most powerful techniques you have at your disposal is the denial test. Before we go into the details of the test, let’s take a look at some sample Assumption question stems:
“The commentator’s argument relies on which of the following assumptions?”
“The official’s conclusion logically depends on which of the following assumptions?”
“Which of the following is an assumption made in drawing the conclusion above?”
Again, all of these questions are asking you to find an answer choice that contains a missing assumption of the argument.
The denial test allows you to confirm that you’ve chosen the right answer choice. The test is very simple: just negate the answer choice you’ve chosen. The negation of the correct answer must weaken the argument. While it certainly isn’t efficient to negate every answer choice, the denial test can be extremely useful when debating between two tempting answer choices.
Let’s consider the following argument:
Joe is an American. Therefore, Joe probably likes country music.
Let's say we want to find the missing assumption in this argument. We can use the denial test to evaluate the following two competing assumptions:
a) Some Americans like country music.
b) All Americans like country music.
Both of these choices connect the evidence (“Joe is an American”) to the conclusion (“Joe probably likes country music.”) But only one of them is a necessary condition, i.e., an assumption, of the conclusion.
Let’s negate statement A first. Be careful: “Some Americans do NOT like country music” is NOT an actual negation of the original statement. Negations must contradict the original statement. The statement “Some Americans do NOT like country music” does not contradict the statement “Some Americans like country music”; in fact, the two statements are compatible. The negation of “some” is “none”, so the negation of Statement A should actually be, “No Americans like country music.” This negation clearly destroys the argument. If not a single American likes country music, then it is definitely flawed to conclude that Joe probably does. Looks like this Statement A is our answer -- but let’s check Statement B with the denial test just to be sure.
Again, be careful: the negation of “all” is NOT “none.” Clearly, “none” contradicts “all”, but when doing negations, we want the weakest possible statement that contradicts the original. If I wanted to disprove the second statement, I would not need to learn about the musical tastes of every American. All I would need would be one American who did not like country music, and I would have proved the claim false. So the negation of “All” is “Not all Americans like country music” or “Some Americans do not like country music.” These statements do not destroy the argument, because they still allow for the possibility that a majority of Americans like country music and that the conclusion about Joe is a reasonable one. Therefore, statement B isn’t a correct assumption.
Thanks to the denial test, we can confidently choose statement A as our correct assumption.
Next time, I’ll blog about negating some actual GMAT answer choices. But for now I hope I’ve given you a little bit of insight to an often overlooked part of mastering the Verbal section.