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Main Idea Questions

The main idea of a passage typically comes at the end of a paragraph. It tends to be the last—occasionally the first—sentence of the first paragraph. If it’s not there, it will probably be the last sentence of the entire passage. Main idea questions are usually the first questions asked.
Some common main idea questions are
  • Which one of the following best expresses the main idea of the passage?
  • The primary purpose of the passage is to.
  • In the passage, the author’s primary concern is to discuss.
Main idea questions are rarely difficult; after all the author wants to clearly communicate her ideas to you. If, however, after the first reading, you don’t have a feel for the main idea, review the first and last sentence of each paragraph; these will give you a quick overview of the passage.
Because main idea questions are relatively easy, the MCAT writers try to obscure the correct answer by surrounding it with close answer-choices (“detractors”) that either overstate or understate the author’s main point. Answer-choices that stress specifics tend to understate the main idea; choices that go beyond the scope of the passage tend to overstate the main idea.

The answer to a main idea question will summarize the author’s argument, yet be neither too specific nor too broad.

In most MCAT passages the author’s primary purpose is to persuade the reader to accept her opinion. Occasionally, it is to describe something.

The primary purpose of the passage is to

  1. explain why the inquisitorial system is the best system of criminal justice
  2. explain how the adversarial and the inquisitorial systems of criminal justice both evolved from the system of private vengeance
  3. show how the adversarial and inquisitorial systems of criminal justice can both complement and hinder each other’s development
  4. analyze two systems of criminal justice and deduce which one is better
The answer to a main idea question will summarize the passage without going beyond it. (A) violates these criteria by overstating the scope of the passage. The comparison in the passage is between two specific systems, not between all systems. (A) would be a good answer if “best” were replaced with “better.” Beware of extreme words. (B) violates the criteria by understating the scope of the passage. Although the evolution of both the adversarial and the inquisitorial systems is discussed in the passage, it is done to show why one is superior to the other. As to (C), it can be quickly dismissed since it is not mentioned in the passage. Finally, the passage does two things: it presents two systems of criminal justice and shows why one is better than the other. (D) aptly summarizes this, so it is the best answer.

Following is a mini-passage. These exercises are interspersed among the sections of this chapter and are written to the same specifications as actual MCAT passages, but are one-quarter to one-half the length. Because the mini-passages are shorter and designed to test only one issue, they are more tractable than a full passage.

Application: (Mini-passage)

As Xenophanes recognized as long ago as the sixth century before Christ, whether or not God made man in His own image, it is certain that man makes gods in his. The gods of Greek mythology first appear in the writings of Homer and Hesiod, and, from the character and actions of these picturesque and, for the most part, friendly beings, we get some idea of the men who made them and brought them to Greece.
But ritual is more fundamental than mythology, and the study of Greek ritual during recent years has shown that, beneath the belief or skepticism with which the Olympians were regarded, lay an older magic, with traditional rites for the promotion of fertility by the celebration of the annual cycle of life and death, and the propitiation of unfriendly ghosts, gods or demons. Some such survivals were doubtless widespread, and, prolonged into classical times, probably made the substance of Eleusinian and Orphic mysteries. Against this dark and dangerous background arose Olympic mythology on the one hand and early philosophy and science on the other.
In classical times the need of a creed higher than the Olympian was felt, and Aeschylus, Sophocles and Plato finally evolved from the pleasant but crude polytheism the idea of a single, supreme and righteous Zeus. But the decay of Olympus led to a revival of old and the invasion of new magic cults among the people, while some philosophers were looking to a vision of the uniformity of nature under divine and universal law.
From Sir William Cecil Dampier, A Shorter History of Science, ©1957, Meridian Books.

The main idea of the passage is that

  1. Olympic mythology evolved from ancient rituals and gave rise to early philosophy
  2. early moves toward viewing nature as ordered by divine and universal law coincided with monotheistic impulses and the disintegration of classical mythology
  3. early philosophy followed from classical mythology
  4. the practice of science, i.e., empiricism, preceded scientific theory

Most main idea questions are rather easy. This one is not—mainly, because the passage itself is not an easy read. Recall that to find the main idea of a passage, we check the last sentence of the first paragraph; if it’s not there, we check the closing of the passage. Reviewing the last sentence of the first paragraph, we see that it hardly presents a statement, let alone the main idea. Turning to the closing line of the passage, however, we find the key to this question. The passage describes a struggle for ascendancy amongst four opposing philosophies: (magic and traditional rites) vs. (Olympic mythology) vs. (monotheism [Zeus]) vs. (early philosophy and science). The closing lines of the passage summarize this and add that Olympic mythology lost out to monotheism (Zeus), while magical cults enjoyed a revival and the germ of universal law was planted. Thus the answer is (B).


As to the other choices, (A) is false. “Olympic mythology [arose] on one hand and early philosophy and science on the other” (closing to paragraph two); thus they initially developed in parallel. (C) is also false. It makes the same type of error as (A). Finally, (D) is not mentioned in the passage.

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