Some of the trickiest questions on the PSAT/SAT Critical Reading section are inference questions. One of the most important things you need to do well on the PSAT/SAT is the ability to tell the difference between an inference and an assumption. College Board, the governing body of the SAT, specifically designs Critical Reading questions to test students’ command of the difference between these two types of answer choices. Though this type of question can be confusing, the answer can often be arrived at logically.
In the context of a standardized test, an assumption is an answer you arrive at by relying on your knowledge of the external world; assumptions are never backed up by evidence from the text itself. Even if factually correct, assumptions are always incorrect answer choices on standardized tests. For the purposes of answering questions correctly on these exams, never ever choose an answer choice that is not supported by the text. Inferences, on the other hand, are always backed up by a quote from the passage and are always better answer choices than assumptions.
Consider this simple example:
The river runs through Natchez and Baton Rouge before emptying into the Gulf of Mexico near New Orleans.
Based on the passage, which is the best answer?
a) Natchez is not a coastal town
b) Natchez is in Mississippi
The correct answer is (a). This is because we may infer from the information that has been given to us that Natchez lies upstream from Baton Rouge and New Orleans, and thus is not located on the coast. Notice that though answer choice (b) is factually correct, it is NOT supported by any evidence in the text and therefore is not the best answer choice. You may know Natchez is in Mississippi, but that information is not mentioned in the text, so it is wrong!
Remember this one essential lesson when trying to determine whether an answer choice is an assumption or an inference: if you can find it in the text then it is an inference, if not then it is an assumption.