Legos, you say? Yep. But before we get into building blocks, take a shot at reading this long GRE passage, taken from the ETS Verbal Practice book pg. 30.

When a passage seems hard to read (and this one is hard to read for most people), I find it helpful to think about a few premises:

1. Understanding the purpose of passages, paragraphs, and sentences allows us to comprehend the passage without full understanding of the content.
2. There are not many different kinds of purposes for passages, paragraphs, and sentences - and once you recognize the common types, you'll get faster at identifying them in the wild with some training.
3. Our goal, then, is to understand the topic only in layman's terms, but to have a handle on the purpose of the passages and its paragraphs. We can use the purposes of sentences to help us do this - picture building a structure out of Legos.

If you can view a sentence as a Lego - a structural component (same for a paragraph) - and identify the purpose of that component, you can free up a lot of short-term memory that would otherwise be used trying to process the often esoteric subject matter in the sentence.

Above, I've numbered the sentences in the passage, and below, I'll give you the purpose of each, then the purpose of each paragraph, and finally, of the passage.

1. Bring up a puzzle
2. Related fact
3. Related (contrary) fact
4. The question we're trying to answer
5. Brings up a potential answer to the question. ("It would seem unlikely" = it actually is likely)
6. Related fact (that starts suggesting it is likely)
7. Related fact
8. Continues the discussion of the potential answer in sentence #5.
9. More about the potential answer
10. Example illustrating the potential answer
11. Uh oh - we've got a problem with the previous paragraph's explanation.
12. More about that problem.
13. Even more about that problem.
14. Example that seems to contradict the problem.
15. Whoops - actually it illustrates the problem now that we get more info about it.
16. Old theory bad. New theory is introduced.
17. Presentation of study probably being used to illustrate new theory.
18. More explanation of new theory using an example.
19. Potential explanation of discrepancy in the study results.
20. Oh shit - the new theory doesn't really explain the puzzle after all.

Paragraph 1: Gives us background info and poses a question / puzzle.

Paragraph 2: Potential explanation / theory to explain puzzle.

Paragraph 3: Criticizes explanation in pgh. 2.

Paragraph 4: Brings up new theory / says it doesn't fully work, either.

Passage: Issue + Theories. This is one of the three passage types I see on the test. Authors generally either present theories, opinions, or just information if we consider the overall purpose of GRE passages.

The typical paragraph purposes I see are:

1. present topic or background info
2. present opinion
3. present theory
4. continue the discussion of the previous paragraph
5. criticize opinion
6. criticize theory
7. talk about implications of something
8. present concession

Sentences follow similar patterns (see my breakdown of the snails passage above). In addition to doing all the same things paragraphs do, they also often do two things after something is presented:

1. elaborate
2. give examples

The GRE asks us to consider the function of sentences as a question type, which is covered in the Critical Reasoning part of this course.