GMAT Critical Reasoning Inference vs Assumption

[by Resham George]

GMAT students often find it difficult to differentiate between inferences and assumptions. This occurs because both assumptions and inferences are characterized as things that ‘must be true’. Additionally, inferences and assumptions aren’t clearly stated or presented in the argument, making it difficult to determine them.

Assumptions are unproven and unstated conditions that must be true for the conclusion to be valid. If the assumption is untrue, the conclusion is invalid. Looking at the example below, one assumption is that people are following the law and wearing their seatbelts. Another assumption is that the use of seatbelts does not affect the number of accidents.

Inferences are beliefs based on an examination of the facts given in the argument. An inference can relate to the whole or part of the argument. Using the example below, an inference is that the mandatory use of seatbelts has significantly reduced the number of life-threatening injuries from road accidents in the state of A.


Argument: The state of A has recently made the wearing of seatbelts mandatory. Although the number of accidents has remained the same, there has been a significant decrease in serious and fatal injuries caused by accidents.

What are some possible assumptions and inferences of this argument?

A useful way to organize the argument is to create a mental map. This is made up of the premises and conclusions of the argument. In this sequence, the assumption would be placed after the premise and before the conclusion. The inference would come after the conclusion.

GMAT assumption questions typically have the following stem: ‘Which of the following is an assumption on which the argument depends?’ In assumption questions, the conclusion is clearly defined. You can use this conclusion as a starting point for your brainstorming.

GMAT inference questions generally use the following question stem: ‘If the statements above are true, which of the following must be true?’ Inference questions in the GMAT do not usually have stated connections with the question stem or the argument. You must generate your own inferences by analyzing the argument.


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