GMAT Critical Reasoning Question Types

GMAT Critical Reasoning Question Types

Assumption Questions: Part 1 – Identifying and Checking Assumptions

These two posts will provide the most important information and practice you need to deal effectively with assumption questions in the Critical Reasoning section. This first post will introduce you to the notion of assumption as applied in the GMAT and will teach you find and double-check correct answers to assumption questions.

Assumption questions are often considered some of the hardest among GMAT Critical Reasoning questions, and this comes as no surprise because these questions can be tricky indeed. In GMAT Critical Reasoning problems, an assumption is information not stated in the argument that has to be true in order for the argument's logic to hold. Simply put, an assumption is something the argument takes for granted in reaching its conclusion. Look at this very simple argument to demonstrate what we have just said.

All kids are excited when they get new toys. Therefore, Tim will be thrilled when he gets the new radio-controlled car we bought him.

This argument has a small gap (scope shift) between the evidence and the conclusion. The evidence is about kids, and the conclusion based on this evidence is about Tim. One thing this argument expects you to take for granted, therefore, is that Tim is a child. Without assuming this, the argument would make no sense, so the argument must assume that Tim is a child.

This example demonstrates two more important characteristics of assumptions, which will help you double-check your answers.

1. Adding the correct assumption to the argument will strengthen the argument.

2. Adding the negated assumption to the argument will weaken the argument.

Let's first try to add our assumption to the argument:

All kids are excited when they get new toys. Tim is a child. Therefore, Tim will be thrilled when he gets the new radio-controlled car we got him.

This argument is stronger because the new premise (assumption) eliminates the gap between the evidence and the conclusion. Now the evidence (first premise) is about children, and the second premise includes Tim in that category, making the evidence directly applicable to Tim.

[Note: Even though the correct assumption will strengthen the argument, not every answer that strengthens the argument must be assumed. (Remember: all squares are rectangles but not all rectangles are squares. Beware of logical fallacies.)]

Now, see what happens if you negate the assumption and add it to the argument:

All kids are excited when they get new toys. Tim is not a child. Therefore, Tim will be thrilled when he gets the new radio-controlled car we got him.

The argument is weaker because its conclusion has become purely speculative. You have no logical grounds to predict anything about Tim's reaction, because the second premise (assumption) does not now connect the first premise (evidence) to the conclusion.

Here's what you must remember about assumptions, based on what's covered here…

1. An assumption isinformation not stated in the argument that must be true for the argument's conclusion to hold. An assumption is unstated vital information that the argument takes for granted.
2. When the correct assumption is added to the argument, it will strengthen the argument. HOWEVER, not every answer choice that strengthens the argument must be assumed.
3. When the correct assumption is negated, adding it will weaken the argument.

Paying attention to these three rules of thumb will help you identify and double-check the correct answers to GMAT Critical Reasoning assumption questions. Here is a real problem for you to solve using these techniques. Allow yourself slightly less than two minutes to attempt this question on your own, and then read the official explanation.

Although many doubts have been raised as to the accuracy of age estimation for a recently found African artifact, all this criticism has no grounds. To estimate the age of the artifact, archeologists used a radiocarbon dating method known to be highly accurate in estimating the age of organic materials.

The conclusion above depends on which of the following assumptions?

A) Modern dating methods are generally more accurate than older dating methods.

B) Written records report that artifacts similar to the one recently found were being used at the time indicated by radiocarbon dating method.

C) The recently uncovered African artifact is made of organic material.

D) Some of the scientists who doubt the accuracy of the age estimations are very young.

E) Radiocarbon dating cannot accurately estimate the age of objects and materials that are more than 60,000 years old.

This is not a very hard question, but before you try to predict a correct answer, analyze the argument to see what was concluded and what evidence was offered to support that conclusion. The argument concludes that criticism has no grounds, that the age estimation was accurate. This conclusion is supported by a single piece of evidence: the radiocarbon dating method used is highly accurate in estimating the age of organic materials.

If you were careful, you noticed that the evidence was somewhat limited; specifically, the method was said to be accurate in dating ORGANIC materials. To conclude that the method was accurate for the African artifact, the argument must assume that the artifact was organic OR that the method effectively used for dating organic materials is equally effective when it comes to dating non-organic materials. The correct answer choice therefore must be an assumption that creates one of those connections.

A) Modern dating methods are generally more accurate than older dating methods. This choice is clearly irrelevant to the argument, since the one method discussed is not compared to any others. You can eliminate this option without further testing it.

B) Written records report thatartifacts similar to the one recently found were being used at the time indicated by radiocarbon dating method. This one may be tempting because such information, if added to the argument, would strengthen it. Remember, however, not every strengthening option must be assumed. Test this option by negating it to see whether it ruins the argument's logic.

• The criticism has no grounds.
• No written records report that artifacts similar to the one recently found were being used at the time indicated by radiocarbon dating.
• Radiocarbon dating is highly accurate for estimating age of organic materials.

Well, you can see that although adding this information might strengthen the argument, it is not information that must be assumed. Even if the information is not true, the argument could still be valid.

C) The recently uncovered African artifact is made of organic material. Correct. If you add this information to the argument, you strengthen it by connecting the stated evidence to the stated conclusion. If you negate this information and say that the recently uncovered African artifact is NOT made of organic material, then your evidence becomes irrelevant, as you know only that radiocarbon dating works for organic materials but have no idea whether it would have worked on the non-organic artifact.

D) Some of the scientists who doubt the accuracy of the age estimations are very young. Even if they all were very old, this would not change a thing, at least as long as you don't have information that links scientists' age and validity of their doubts.

E) Radiocarbon dating cannot accurately estimate the age of objects and materials that are more than 60,000 years old. You don't know the age estimated, so this information is irrelevant.

This concludes our first post on assumption questions, but we will continue this topic, examining the most common types of assumptions made by GMAT arguments and giving you some more practice questions.