As with inference questions, purpose questions deal with information that isn’t directly stated. But while inference questions ask you to draw conclusions about the subject matter, purpose questions will ask you about the reason that an author says something or phrases something in a particular way, or they may ask more generally about why a passage is organized the way it is.
ETS recommends that you learn these words and phrases, which are useful in understanding purpose questions and answer choices. I recommend you learn them because they’re good academic words to use in your writing.
Most purpose questions will ask you to choose whether a given phrase provides an example, provides a counter-example, explains, or provides an exception to a statement made in the passage. Check out this example (source).
Why does the author mention that “the Dutch were restricted to Dejima”?
(A) To provide evidence of Japan’s refusal to trade with other European countries
(B) To note an example of another country which limited its own international interactions
(C) To illustrate the severity of limits imposed by Japan’s isolationism
(D) To elaborate on the importance of a particular Japanese island in the period of sakoku.
First, let’s look at the specific sentence in full: “Only a small amount of trade with China, Korea, and the Netherlands was permitted, and the Dutch were restricted to Dejima, an artificial island in the harbour at Nagasaki.” Consider the function of this sentence and the main message of the paragraph in full. How does this sentence relate to the rest of the text?
(A) doesn’t make sense because this sentence is telling us who the Japanese did trade with. The fact that Japan traded with the Dutch does not mean that they didn’t trade with other countries. This is a very good-looking answer, one you should think carefully about, because it is in line with the general meaning of the paragraph. But it’s not connected to the information in the specific sentence, and that causes a problem.
To cross (B) off, it’s key to understand that “another country” means the Dutch and “its own” means that they limit themselves; the Dutch limit the Dutch. That’s factually false.
The sentence that I copied above suggests that (C) is the correct answer. Japan’s isolationism was very strict. They only traded with three countries. And even within those countries, one country (the Netherlands, also called “the Dutch”) could only trade on a single, specified island. In other words, they were very restricted, and the author is showing exactly how restricted.
As for (D), the island may have been important, but that’s not the purpose of the paragraph. The island is not mentioned in any other place, and it is not the author’s focus. So (C) must be the correct answer.