TACHS: Comparison passages: sort what is shared from what differs
Learn to answer questions about a passage that compares two things by sorting shared features from the one difference the writer stresses, and by checking both halves of every two-part choice.
When a passage compares two similar things, how do you pick the main difference from choices that all sound like differences?
Short answer
Sort the features into same and different, then find the difference the writer names. Check each half of a choice against the right item, and cross out any choice built on a shared feature or a difference the passage never mentions.
Know first: Telling similarities from differences, Words such as both, while, however and differ
Step 1 of 5
Most comparisons share a lot and differ in one key way
Comparison passages describe two things side by side: two games, two methods, two places. Usually the writer makes the shared features clear early, then focuses on one key difference.
Contrast choices often come in two halves joined by a semicolon or while. Both halves must be true, and each must belong to the right item.
| Step | What to do | Watch for |
|---|---|---|
| Same list | Put every shared feature here | A choice that calls a shared feature a difference |
| Different list | Note what the writer says changes | differ, but, however, adds, while |
| Writer's summary | Find the line that names the difference | They differ in..., Both aim to... |
| Two-part choice | Check each half on its own | One true half paired with a false or swapped one |
The same two lists answer detail, cause and summary questions about the comparison.
Step 2 of 5
Sort before you choose
Two gardens
Two community gardens on the same street grow tomatoes in the same kind of soil1. At the Elm Street garden, volunteers water on a fixed schedule2 posted on the shed door. At the Park Lane garden, volunteers check a moisture meter each morning and water only when the reading shows dry soil3. Both gardens want healthy plants; they differ in how they decide when to water4.
- Same list: street, crop, soil.
- Elm Street's side of the difference.
- Park Lane's side of the difference.
- The writer's summary names the difference.
Worked example: What is the main difference?
What is the main difference between the two gardens?
- AElm Street uses richer soil; Park Lane uses sandy soil.
- BElm Street waters on a set schedule, while Park Lane waters based on daily soil readings.
- CPark Lane grows more tomatoes than Elm Street.
- DElm Street never waters its plants; Park Lane waters them every day.
- 1
Same list
The street, the tomatoes, the soil, the goal of healthy plants.
- 2
Different list
How each garden decides when to water.
- 3
Check both halves
B: Elm Street uses a schedule, true. Park Lane uses readings, true.
- 4
See why the other choices are there
A names soil, which is shared. C compares harvests, which the excerpt never mentions. D has two false halves: Elm Street does water, and Park Lane waters only when the soil is dry.
Answer
Elm Street waters on a set schedule, while Park Lane waters based on daily soil readings.
Wrong: Park Lane waters every day, while Elm Street waters on a schedule.
Right: Park Lane waters only when the soil is dry, while Elm Street waters on a schedule.
The second half is the same in both. The first half of the wrong version changes one detail, and that is enough to make the whole choice false.
Step 3 of 5
Compare two programs yourself
Read this excerpt
The town library runs two summer reading programs. Both last eight weeks, both ask readers to report at the front desk once a week, and both give a prize at the end. In Reading Trail, every reader gets the same list of ten books and finishes them in order. In Open Shelf, readers choose any books they like and record how many minutes they read. The programs differ mainly in who chooses the books.
Check yourself · Question 1
What is the main difference between the two programs?
Answer: B
The last sentence names the difference: who chooses the books. Reading Trail gives everyone one list, and Open Shelf lets readers pick.
Trap answer: Reading Trail requires weekly reports; Open Shelf does not.
A shared feature presented as a difference
- Why it looks right
- Reports and rules sound like the kind of thing two programs would differ on.
- Why it's wrong
- The second sentence says both ask readers to report once a week. That's on the same list.
- The right answer
- Reading Trail assigns the same books to everyone, while Open Shelf lets readers choose.
Check yourself · Question 2
Based on the excerpt, why might a reader who wants to read only mystery novels prefer Open Shelf?
Answer: A
Open Shelf lets readers choose any books, so a reader could pick only mysteries. Reading Trail's fixed list wouldn't allow that.
Common mistake
I checked the first half of a two-part choice and picked it.
- Why it's tempting
- Once one half matches, the whole choice looks right, especially when time is short.
- Do this instead
- Check each half separately against the right item. One false or swapped half makes the whole choice wrong.
Step 4 of 5
What to remember
Remember
- Sort features into same and different before you look at the choices.
- Find the line where the writer names the difference, often with differ, while or both.
- Check both halves of a two-part choice, and reject differences the passage never mentions.
Step 5 of 5
Practice on a real question
Use what you just learned on this question, then check the explanation.
In your own words
In the practice question, which features do the two things share, and which sentence names the difference?