TACHS: Cause and effect: trace the chain back to its first link
Learn to follow a chain of causes in a science or engineering passage, pick the link the question asks about, and tell a cause from an analogy or a limit the writer adds.
How do you find the cause the passage gives when the choices all sound like real science?
Short answer
Find the effect named in the question, then trace backward through the passage's signal words to the cause it gives. The answer is in the passage and on the cause side of the chain.
Know first: What cause and effect mean, Signal words such as because, so and as a result
Step 1 of 5
Science passages build a chain of causes
A cause makes something happen. An effect is what results. Informational passages often build a chain: one fact causes a change, and that change creates a need for something else.
Cause questions come with choices that sound like real science. Some are true in the world but never discussed in the passage. Some reverse the chain. Some name an effect as if it were the cause.
| Signal | What it tells you | Example |
|---|---|---|
| because, since, as | The cause comes next | The road flooded because the drain was blocked. |
| so, therefore, as a result | The effect comes next; the cause is just before | The ice floats. As a result, the water below stays liquid. |
| needs, must, requires | A problem the earlier cause created | The garden needs a fence to keep the deer out. |
| imagine, picture, like | An analogy that explains the cause, not the cause itself | Picture a garden hose with a kink in it. |
Keep asking what produces this until you reach the passage's starting fact.
Step 2 of 5
Follow the signal words backward
Under the ice
On a frozen pond, ice forms at the top first. Water expands as it freezes, so ice is less dense than liquid water and floats.1 The floating layer then slows the loss of heat from the water underneath.2 As a result,3 fish can survive the winter4 in liquid water near the bottom.
- The first link: why the ice stays on top.
- The next link: the ice acts as a cover.
- Signal: the cause is in the sentence just before.
- The effect the question will ask about.
Worked example: Why can fish survive?
According to the excerpt, why can fish survive under a frozen pond?
- AFish move to warmer ponds before winter.
- BThe floating ice slows heat loss, so the water below stays liquid.
- CIce sinks to the bottom and protects the fish.
- DFish eat more food in the fall.
- 1
Name the effect
Fish survive the winter.
- 2
Follow the signal
As a result points back to the sentence before it: the floating layer slows heat loss.
- 3
State the cause
The ice on top keeps the water below from losing heat, so it stays liquid.
- 4
See why the other choices are there
C reverses the chain, since the ice floats. A and D describe things some animals do, but the excerpt mentions neither.
Answer
The floating ice slows heat loss, so the water below stays liquid.
Find the wrong step
A student answers: According to the excerpt, why does ice stay at the top of the pond?
- 1
Names the effect: the ice stays on top.
- 2
Picks it slows the loss of heat from the water underneath, because that sentence is about the ice layer.
What went wrong
That's what the ice does once it's on top, an effect further down the chain. It doesn't explain why the ice is there.
- 3
Moves on to the next question.
The fix
Go one link back: water expands as it freezes, so ice is less dense than liquid water and floats.
Step 3 of 5
Trace the chain yourself
Read this excerpt
A cold can of juice on a summer table soon looks wet, as if it were leaking. The can is sealed, though, and none of the juice gets out. Air holds invisible water vapor. When warm air touches the cold metal, the air cools, and some of its vapor turns into liquid droplets on the outside of the can. On a dry day, fewer droplets form, because the air holds less vapor.
Check yourself · Question 1
According to the excerpt, what causes droplets to form on the can?
Answer: B
The chain: air holds vapor, warm air touches cold metal and cools, and some vapor becomes droplets. The right choice names that cause.
Trap answer: Juice slowly seeps through the metal.
The belief the passage corrects
- Why it looks right
- The first sentence says the can looks as if it were leaking.
- Why it's wrong
- Looks as if sets up a correction. The next sentence says the can is sealed and nothing gets out.
- The right answer
- Water vapor in the air cools against the cold metal and turns into liquid.
Check yourself · Question 2
What does the last sentence of the excerpt add?
Answer: B
The last sentence says fewer droplets form when the air is dry, because the air holds less vapor. It narrows the explanation without taking it back.
Common mistake
I picked a fact I know is true in real life.
- Why it's tempting
- If you've learned it in science class, it feels like it has to be right.
- Do this instead
- Check that the choice is in the passage and on the cause side of the chain. Outside facts can be true and still be wrong here.
Step 4 of 5
What to remember
Remember
- Name the effect, then follow the signal words back to the cause the passage gives.
- Make sure your choice is the right link: one step before the effect the question names.
- An analogy illustrates a cause, and a not all or some sentence limits a claim without reversing it.
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, what effect did the question name, and which sentence of the passage gives its cause?