GMAT Critical Reasoning – Assumption vs Inference

We need to discuss an important distinction between assumptions and inferences. Most of you will be able to explain the difference between an assumption and an inference but some questions will still surprise you. After all, both assumptions and inferences deal with the same elements in the argument. The way they are worded makes all the difference.

In simple words, when you have enough data given and you can infer something from it without doubt, it is called an inference/conclusion.
When you have author’s opinion (conclusion of the argument) and you need something to be true for the opinion to hold, that is an assumption.

Structure of an Assumption vs an Inference in GMAT

Let us explain with a simple example.

All A are B.
All B are C.

You can conclude that: All A are C. This must be true. It is a conclusion.

If you conclude that ‘All C are A’ (your opinion, not necessarily a fact), you are assuming that A, B and C overlap i.e. they all have exactly the same elements.

Look again:

Argument 1:

Premises:

All A are B.
All B are C.

Conclusion: All A are C.

Argument 2:

Premises:

All A are B.
All B are C.

Conclusion: All C are A.

Assumption: A, B and C overlap.

The conclusion of argument 2 will not hold if the assumption is negated.

Identifying the GMAT Critical Reasoning Question Type

On some questions, people find it hard to type the question as inference or assumption. Such questions often have the words ‘must be true’. Let’s discuss the two different cases:

1.  If the given statements are true, which of the following must also be true?

2.  Which of the following must be true for the argument to hold?

These are two different questions – The first one asks you to find the option which must be true given that the statements in the argument are true i.e. what can you infer from the argument? Here you are looking for the inference of the argument.

The second one asks you to find the option which must be true for the argument i.e. conclusion of the argument to hold i.e. what is necessary for the conclusion to hold. The statement that is necessary for the conclusion to hold is called an assumption so basically we are looking for the assumption here.

Illustration of the Confusion Between Assumption vs Inference in GMAT

Let’s look at a question which often raises the inference vs assumption debate.

Question: According to psychoanalytic theory, people have unconscious beliefs that are kept from becoming conscious by a psychological mechanism termed “repression.” Researchers investigating the nature of this mechanism observed occasions on which a patient undergoing therapy became aware of and expressed a previously unconscious belief. They found that such occasions were marked by an unusual decrease in the patient’s level of anxiety.

If the information above is true, and if the researchers’ investigation was properly conducted, then which of the following must also be true?

(A) Changes in the patient’s anxiety level during therapy can generally be used as an accurate measure of the extent to which the patient is becoming conscious of previously repressed beliefs.

(B) Even when one of a patient’s unconscious beliefs remains unconscious, researchers are sometimes able to discover this belief.

(C) If psychoanalytic theory is correct, then most conscious beliefs originate as unconscious beliefs.

(D) Researchers were able to distinguish expressed beliefs that had previously been unconscious from those that had long been conscious but that the patient had not previously expressed.

(E) Although the beliefs on which the mechanism of repression works are all unconscious, the operation of the mechanism itself is something of which patients are consciously aware.

Solution:

As suggested in our CR book, it might be a good idea to first read the question stem to figure out the type of question.

“If the information above is true, and if the researchers’ investigation was properly conducted, then which of the following must also be true? “

The word ‘also’ is a dead giveaway. The statements are true – which of the following must also be true. We are looking for an inference – since the statements are true, what else is true based on the statements? i.e. what is the inference?

So the question is an inference/conclusion question. Great!

Let’s focus on the stimulus now.

Premises:

• Psychoanalytic theory says that people have unconscious beliefs that are kept from becoming conscious by repression.
• Researchers investigating repression observed occasions on which a patient undergoing therapy became aware of and expressed a previously unconscious belief.
• They found that such occasions were marked by an unusual decrease in the patient’s level of anxiety.

We are looking for something we can infer from these statements. Let’s look at the options.

(A) Changes in the patient’s anxiety level during therapy can generally be used as an accurate measure of the extent to which the patient is becoming conscious of previously repressed beliefs.

The stimulus says that the occasions when patients become conscious of previously repressed beliefs are marked by decreased anxiety. They don’t say that the level of decrease varies directly or is correlated with the level of becoming conscious. Hence we cannot infer this from the stimulus.

(B) Even when one of a patient’s unconscious beliefs remains unconscious, researchers are sometimes able to discover this belief.

Not relevant to the given statements. Whether there are other mechanisms of identifying unconscious beliefs is out of scope.

(C) If psychoanalytic theory is correct, then most conscious beliefs originate as unconscious beliefs.

Again, not relevant. All we can say is that people can be made to express some unconscious beliefs through therapy. We cannot say that all conscious beliefs originate as unconscious.

(D) Researchers were able to distinguish expressed beliefs that had previously been unconscious from those that had long been conscious but that the patient had not previously expressed.

The given stimulus tells us that the researchers have been able to make people express their unconscious beliefs through therapy. A valid point here is – how do researchers know that the beliefs being expressed by the patients are unconscious beliefs and not merely conscious beliefs that the patients did not express previously? Since the stimulus says, “Researchers investigating repression observed occasions on which a patient undergoing therapy became aware of and expressed a previously unconscious belief” and we have to take the statement to be true, it means they were able to distinguish between unconscious beliefs and conscious but unexpressed beliefs. Hence (D) is the answer.

(E) Although the beliefs on which the mechanism of repression works are all unconscious, the operation of the mechanism itself is something of which patients are consciously aware.

Focus on the first part of this option. The statements in the stimulus tell us that repression keeps unconscious beliefs unconscious. They don’t tell us whether repression works on conscious beliefs or not – perhaps it keeps people from expressing conscious beliefs or perhaps it doesn’t work on conscious beliefs at all – the statements don’t say. We cannot say that the beliefs on which repression works are ALL unconscious. Hence we cannot infer this. Not the answer.

The correct answer is (D). 

Hope you will keep this in mind next time you come across a ‘must be true’ question.

An Official GMAT Question to Ponder Upon: Assumption or Inference?

Here is an official question that might help you understand the reasons for our misgivings. We will give you the argument but not the question stem. We will also give you the correct answer. You will need to decide whether the question stem asks for a conclusion or an assumption.

Question: Among the more effective kinds of publicity that publishers can get for a new book is to have excerpts of it published in a high-circulation magazine soon before the book is published. The benefits of such excerption include not only a sure increase in sales but also a fee paid by the magazine to the book’s publisher.

(A) The number of people for whom seeing an excerpt of a book in a magazine provides an adequate substitute for reading the whole book is smaller than the number for whom the excerpt stimulates a desire to read the book.

(B) Because the financial advantage of excerpting a new book in a magazine usually accrues to the book’s publisher, magazine editors are unwilling to publish excerpts from new books.

(C) In calculating the total number of copies that a book has sold, publishers include sales of copies of magazines that featured an excerpt of the book.

(D) The effectiveness of having excerpts of a book published in a magazine, measured in terms of increased sales of a book, is proportional to the circulation of the magazine in which the excerpts are published.

(E) Books that are suitable for excerpting in high-circulation magazines sell more copies than book that are not suitable for excerpting.

The correct answer is (A). What is the question?