Idea cohesion

One of the most challenging question types on the ACT comes down to this:

The author is considering removing/adding the previous/following sentence. Should he/she and why?

Or, asked another way:

The author is considering removing the preceding text. If the author were to do so, the passage would primarily be losing what?

These questions feel subjective because they ask you to judge how well a sentence fits. But they aren’t opinion-based. There are correct answers - you just have to base your judgment on the passage’s goals.

Before you can answer these questions consistently, you need to understand one key word: purpose. These questions test whether you can identify the purpose of a passage, paragraph, or sentence, and how those purposes connect. For example, how does the purpose of one sentence support the purpose of the whole passage?

Example

Let’s get specific. Read the passage once quickly, then we’ll break it down.

[1] It was my first time in South Florida and I wanted to see an Oustalet’s chameleon. My husband knew that this was the only way he’d ever convince me to move here, and so he obliged. After securing permission, we headed to a nearby avocado farm with our headlamps ready.

[2] Oustalet’s chameleons have only ever been found in two places: Madagascar, where they are native, and Homestead, Florida, where they are non-native. Searching through those avocado trees did remind me of searching for lizards in Madagascar. Especially at night, these two places - Madagascar and South Florida - seemed similar to me. I looked around the avocado trees and saw some perfect nighttime perches for sleeping chameleons. No wonder these lizards survived here in Homestead.

[3] We didn’t find any Oustalet’s chameleons that night. Although I went back to our hotel room disappointed, I knew it was great news for Florida. The fewer invasive species found here, the better. Invasive species are bad news. They are able to spread aggressively outside their natural range and can cause local extinctions of native species.

[4] The cost of invasive species is high. One study in 2005 found that invasive species cost the United States more than $120 billion in damages each year. Once an invasive species becomes established, eradication is incredibly difficult. And the economic costs of invasive species are small compared to the ecological ones. Burmese pythons are a perfect example. [*] They were introduced from the pet trade into the Everglades in the 1980s. They are known predators of many native birds and mammals and it seems unlikely that we will be able to completely eradicate them in the near future. They get a lot of attention, but there are many other invasive species - the New Guinea flatworm, Brazilian pepper plants, exotic fish and non-native snails - that also concern the state authorities.

[5] Florida’s invasive species problem is not going away anytime soon. As for me, I have yet to find an Oustalet’s chameleon in Homestead. The longer I’m here, the less I want to see one, anyway. I’ve learned that our native species have a lot more to offer.

Analyzing for purpose

Start by identifying the purpose of the passage as a whole. In ACT passages, the main purpose usually shows up in one (or more) of these ways:

1. It states an important idea early and then spends the rest of the passage exploring, explaining, and/or analyzing it.
2. It builds up to an important idea and states it near the end.
3. It repeats the important idea several times (often in different wording).

So what’s happening in this passage? It’s mostly a combination of options 2 and 3. The passage repeatedly mentions both “chameleons” and “invasive species,” and it returns to those ideas at the end.

Notice, though, that “invasive species” is the bigger topic. The chameleons matter because they’re an example of an invasive species. So a clear statement of the passage’s purpose might be: to inform the reader about the impact of invasive species and explore an example (Oustalet’s chameleon).

You need the purpose of the whole passage so you can judge whether a particular sentence supports that purpose.

Example

Consider the second sentence of paragraph 3:

Although I went back to our hotel room disappointed, I knew it was great news for Florida.

If the author removed this sentence, the passage would be primarily missing:

A. An important detail about techniques for searching for chameleons
B. Distracts from the purpose of the passage - it shouldn’t be included
C. Concludes the narrative about searching for chameleons in Florida
D. A link between the narrator’s experience and important information about the topic

Start by eliminating choices that don’t match the passage’s purpose.

• A doesn’t fit because the passage isn’t about how to search for chameleons.
• B doesn’t fit because the sentence supports the passage’s main point; it doesn’t distract from it.

That leaves C and D, and both sound plausible:

• The sentence does wrap up the narrator’s disappointment about not finding a chameleon (C).
• It also connects the narrator’s experience to the larger point about invasive species (D).

When two answers are both partly true, use the wording of the question to decide. The question asks what the passage would primarily be missing. That pushes you toward the passage’s main purpose.

Is the passage mainly about the narrator’s search story, or mainly about invasive species? It’s mainly about invasive species. The search story is there to set up and support that topic.

So the best answer is:

Example

Let’s look at one more.

Note the asterisk in paragraph [4]. Here, the author is considering adding the following true sentence.

Burmese pythons can reach a length of up to 18 feet.

Should the author do so?

A. Yes, it adds information necessary to understand the passage
B. Yes, it add an important detail
C. No, it adds information irrelevant to the passage
D. No, it is unrelated to the information around it

The “Yes” or “No” part is usually straightforward. The harder part is choosing the best reason.

• A is wrong because the python’s length isn’t necessary to understand the passage’s point about invasive species.
• B is also wrong for the same reason. Calling it an “important detail” doesn’t make it relevant to the passage’s purpose.

That brings you to C and D.

• D says the sentence is unrelated to the surrounding information, but that’s not true - the surrounding sentences are about Burmese pythons.
• C is correct because the python’s length doesn’t help the passage explain the impact of invasive species. It’s a true fact, but it doesn’t serve the passage’s main purpose.

So the best answer is: