Idea cohesion

One of the most challenging question types on the ACT boils 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 are challenging because they feel more subjective or more opinion-based. And in fact, they do require you to make a judgment and evaluate the ideas and purpose of the passage. That doesn’t mean, however, that they’re opinion-based or that there aren’t correct answers.

Before we talk about how to answer these questions correctly, we need to understand an important word: purpose. Essentially, these questions are trying to see if you can understand the purpose of a passage, paragraph, or sentence, and sometimes how those purposes relate to each other. How does the purpose of a sentence, for example, relate to the purpose of a whole passage?

Example

Let’s look at specifics. Give the following passage a quick read, and then we’ll look at it in detail.

[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

Let’s start by considering the purpose of the passage as a whole. There are three ways a passage or paragraph will show its primary purpose.

1. It might state an important idea and spend the rest of the time exploring, explaining, and/or analyzing it
2. It might spend most of its time exploring and leading up to an important idea that it finally states at the end.
3. It will make repeated references (usually in different ways) to the important idea.

So which one of these is happening in our example passage? Definitely a combo of options 2 and 3. It mentions both “chameleons” and “invasive species” multiple times throughout the passage and then again at the end to wrap up. We can tell that “invasive species” is a more important topic than “chameleons” here because chameleons are one example of an “invasive species.” So we might say the purpose of the passage is: to inform the reader about the impact of invasive species and explore an example (Oustalet’s chameleon).

We have to know the purpose of the whole passage to understand how a particular sentence or paragraph fits within it.

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

Options A and B are not what we’re looking for. The passage’s purpose is not to discuss techniques for finding chameleons. The passage’s purpose is definitely to explore Florida chameleons as an example of invasive species, so it definitely doesn’t distract from the purpose.

Options C and D are much more difficult to pick between, however, because they are both true. It does conclude the narrative. It also links that narrative to the important passage of the topic. Given that they’re both correct, we need to look at which one is more correct. Note the question: the passage would be “primarily missing.” That means it’s going to be tied to the purpose of the passage. Is the purpose of the passage closer to the narrative or the information about the invasive species? As we said, it’s focused on invasive species. The story about looking for chameleons is only a way to demonstrate the importance of the information about invasive species.

So, do you know what the correct 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

Can you figure out the answer?

Let’s dissect to make sure you understand why you answered this right or wrong.

You would think that “Yes” or “No” is pretty clear, but the reason is more difficult to nail down. This is often true, but sometimes you’ll even be stuck between one of the “yes’s” and one of the “no’s”!

Option A is wrong because knowing the length of the Burmese python is certainly not critical to understanding the impact of invasive species. Their size simply doesn’t factor in, since the main example, the chameleons are not very big.

Option B claims it’s an important detail. Option A and B are the same, basically. Option B is wrong for the same reasons that option A is wrong.

Option C is much closer. If the purpose of the passage is to discuss the impact of invasive species, and Burmese pythons are one (more) example of that; their size doesn’t have much to do with it. We feel pretty confident about option C, but let’s look at all our options.

Option D says that the problem is that it’s not related to the information around it. This isn’t true because the information is in fact about the Burmese python. It’s just not about what the whole passage is trying to be about.

So, C is correct.