Ask yourself: Why is the author telling me this? Why is he selecting the facts and drawing the conclusions that he is? What is the author's agenda?

It may not be to overthrow of the world, but there's always some reason the author wrote the passage. Often essays will have a policy idea or suggestion to fix a problem described. Sometimes, the author might simply want to educate people about a subject or clear up a misconception. And sometimes, there will be a more political/ideological motive for the claims made.

Academic camouflage will often disguise the main idea. Writers try to sound objective, but don't let that fool you. There is always something the author wants to convince you of, or at least, get you to learn from the passage.

Be careful to distinguish fact from opinion. Though they look like facts, some statements in the essay may be false claims or unsupported opinions loaded with bias. Pay close attention to the language in order to distinguish fact from opinion. The author's purpose for writing the essay and his or her convictions are found in these subtle statements of opinion.

Take these excerpts from a passage on water management, for example. Some of the author's statements are fact, but many are opinion. Try this:

4. Find the Big Idea

IV: Question Types