What the question looks like
This skill is in the Craft and Structure domain. College Board describes it as analyzing the structure of a text or finding its main rhetorical purpose. You will see three kinds of stems:
- Which choice best states the main purpose of the text?
- Which choice best states the function of the underlined sentence in the text as a whole?
- Which choice best describes the overall structure of the text?
On this page the sentence you are asked about is shown in bold, because the test underlines it.
The rule: purpose is a verb
What a text says is its main idea. What a text does is its purpose. Purpose answers almost always start with a verb, so read the verbs in the choices first and cross out any that do not match what the author is doing.
| Verb in the answer | What the text or sentence does | Clues in the passage |
|---|---|---|
| describe | Paints a picture of a place, person or event | Sensory details, no argument |
| explain | Shows how or why something works or happens | because, this allows, steps in order |
| challenge or correct | Pushes back on a common belief or earlier view | many people assume, however, in fact |
| give an example | Shows one case of a general claim | for example, a specific name or event after a general statement |
| introduce a contrast or exception | Shows where the general rule fails | but, unlike, an exception |
| present a finding | Reports what a study or researcher found | researchers found, the data showed |
Wrong vs right
| Passage job | Wrong answer | Right answer | Why |
|---|---|---|---|
| A passage says many people think bats are blind, then explains that every bat species can see | To describe how echolocation works | To correct a common belief about bats | Echolocation is a detail. The purpose must cover the whole passage, which is built to fix a mistaken belief. |
| A sentence names milkweed right after a claim that some plants defend themselves with chemicals | It states the main claim | It gives an example of the claim | The claim comes first. The milkweed sentence is one specific case of it. |
Worked examples
Example 1: main purpose
Problem Most people picture bats as blind. In fact, every bat species can see, and many fruit bats rely heavily on their eyesight and sense of smell to find food. Echolocation, which many other bats use to hunt insects at night, works alongside their vision rather than replacing it. Which choice best states the main purpose of the text? Choices: To correct a common belief about bats' eyesight / To explain in detail how echolocation works / To argue that fruit bats are smarter than other bats / To describe the places where bats live
- Say the job in your own words: the text sets up a belief (bats are blind) and then shows it is wrong.
- Check that your summary covers every sentence. The sentences about fruit bats and echolocation both support the point that bats can see.
- Eliminate: echolocation gets one sentence and no detail on how it works. Nothing compares intelligence or describes habitats.
Answer To correct a common belief about bats' eyesight
Example 2: function of one sentence
Problem Ana had practiced the piano piece for weeks. On the night of the recital, she walked onto the stage and sat down. Her hands, which had never failed her at home, would not stop shaking. Then she took a breath, looked at the first line of music, and began to play. Which choice best states the function of the bold sentence? Choices: It describes the setting of the recital. / It introduces a difficulty that the final sentence shows Ana moving past. / It explains why Ana chose this piece of music. / It suggests that Ana had not really practiced.
- Read the sentence before and after. Before: she sits down. After: she breathes and begins to play anyway.
- So the bold sentence creates a problem (nerves), and the last sentence shows her pushing through it.
- Eliminate: it is about her hands, not the room. Nothing explains her choice of music. Never failed her at home actually tells us she did practice.
Answer It introduces a difficulty that the final sentence shows Ana moving past.
Example 3: overall structure
Problem For years, city planners assumed that widening roads would reduce traffic. When cities added lanes, though, traffic often returned to its old levels, because the extra space encouraged more people to drive. Planners call this effect induced demand, and many now look for other ways to ease congestion, such as better bus service. Which choice best describes the overall structure of the text? Choices: It presents an assumption, describes evidence that undercut it, and names the idea that replaced it. / It describes a problem, proposes a solution, and predicts the solution will fail. / It compares two cities and explains why one has less traffic. / It lists the causes of traffic in order of importance.
- Label each sentence with a job. Sentence 1: an old assumption. Sentence 2: evidence against it (though). Sentence 3: the new idea and what planners do now.
- Find the choice whose parts match your labels in the same order.
- The second choice gets the order wrong: no solution is predicted to fail. No two cities are compared, and no ranked list of causes appears.
Answer It presents an assumption, describes evidence that undercut it, and names the idea that replaced it.
Common mistakes and fixes
| Mistake | Fix |
|---|---|
| Picking a choice that is true but only covers one detail | A main purpose must fit the whole passage. Test it against the first and last sentence. |
| Judging one sentence by itself | Function means its job in the passage. Always read the sentence before and after it. |
| Trusting a choice because it repeats words from the text | Choices that copy words often twist the job. Check the verb, not the vocabulary. |
| Choosing strong verbs like argue or criticize for a neutral passage | Match the author's attitude. A text that only reports facts does not argue or attack. |
| Getting the order wrong on structure questions | Write a one-word label for each sentence, then find the choice in that order. |
Practice
Five structure and purpose questions
When a honeybee finds a good patch of flowers, it returns to the hive and performs a waggle dance. The angle of the dance shows the direction of the flowers compared with the sun, and the length of the waggle shows how far away they are. Other bees use this information to fly to the food. Which choice best states the main purpose of the text?
- To argue that honeybees are the most intelligent insects
- To compare honeybees with other pollinators
- To explain how honeybees share the location of food
- To describe the kinds of flowers honeybees prefer
Show answer
Answer: To explain how honeybees share the location of food
Every sentence is about how the dance passes on where food is. The text makes no claim about intelligence, mentions no other pollinators, and does not name any flowers.
Many people think of deserts as places where almost nothing grows. After a wet winter, however, parts of Death Valley can fill with wildflowers. These large blooms, sometimes called superblooms, may appear only once a decade or so. Which choice best states the function of the bold sentence?
- It explains why superblooms happen only once a decade.
- It supports the belief in the first sentence with an example.
- It presents an observation that challenges the belief in the first sentence.
- It describes the weather of Death Valley in detail.
Show answer
Answer: It presents an observation that challenges the belief in the first sentence.
However signals a turn: wildflowers filling the desert goes against the idea that almost nothing grows there. It does not support the belief, it gives no reason for the timing, and one phrase about a wet winter is not a detailed description of weather.
The Great Pacific Garbage Patch is often imagined as a floating island of trash. In reality, most of its plastic is in small pieces spread across a huge area of ocean, which makes it hard to see from a ship or a satellite. This is one reason cleaning it up is so difficult. Which choice best describes the overall structure of the text?
- It compares two different garbage patches in the Pacific Ocean.
- It describes a problem and then proposes a detailed solution.
- It tells the history of the garbage patch from start to present.
- It describes a common image, corrects it, and then explains one result of the correction.
Show answer
Answer: It describes a common image, corrects it, and then explains one result of the correction.
Sentence 1 gives the common image (an island), sentence 2 corrects it (small pieces spread out), sentence 3 gives a result (hard to clean). No solution is proposed, no history is told, and only one patch is discussed.
The house had been empty for years. Ivy covered the windows, and the front steps sagged in the middle like an old mattress. Still, when Marisol pushed open the door, she smelled cinnamon, as if someone had baked bread that morning. Which choice best states the main purpose of the text?
- To describe a place that seems abandoned but holds a surprising sign of life
- To explain why Marisol decided to buy the house
- To show that Marisol is afraid of empty houses
- To compare Marisol's home with the house she visits
Show answer
Answer: To describe a place that seems abandoned but holds a surprising sign of life
The first two sentences show neglect, and Still turns to the cinnamon smell, which suggests someone has been there. Nothing mentions buying the house, fear, or a second home.
Some plants defend themselves with chemicals. Milkweed, for example, contains a bitter, toxic sap that makes most animals avoid eating it. Monarch caterpillars are an exception: they eat milkweed and store its toxins, which makes them taste bad to birds. Which choice best states the function of the bold sentence?
- It introduces an exception to the claim in the first sentence.
- It states the main conclusion of the text.
- It gives a specific case of the general claim in the first sentence.
- It explains why monarch caterpillars taste bad to birds.
Show answer
Answer: It gives a specific case of the general claim in the first sentence.
For example marks milkweed as one case of plants defending themselves with chemicals. The exception (monarchs) and the reason they taste bad both come in the next sentence, so those choices describe a different sentence.
Frequently asked questions
What is the difference between main idea and main purpose?
The main idea is the point the text makes: bats can see. The main purpose is what the author is doing with the text: to correct a common belief about bats. Main idea answers are statements. Purpose answers usually start with to plus a verb.
How do I handle these questions on poems and stories?
Use the same method, but think about what the lines show about a character, a mood or a change. Ask what the reader learns from the lines and why the writer put them there. See poetry and literature passages for more.
Are answers with words like always or never usually wrong?
Often, but not because of the word itself. They are wrong when the passage is not that strong. Check the passage: if it says many or often, a choice that says all or always goes too far. If the passage really is absolute, the strong choice can be right.
Sources
- College Board, Assessment Framework for the Digital SAT Suite, version 3.01 (August 2024), accessed October 1, 2026
- College Board, The Reading and Writing Section, accessed October 1, 2026
